CERNJuly/August 2021 cerncourier.com COURIERReporting on international high-energy physics WELCOME CERN Courier – digital edition Welcome to the digital edition of the July/August 2021 issue of CERN Courier.

Since the early 1980s, successive generations of silicon trackers have driven numerous discoveries (p39). The LHC detectors represent the state of the art in particle-tracking applications, delivering high-granularity data at speed under the most extreme operating conditions imaginable. Containing some 12.5 Gpixels, the recently installed upgraded inner tracker for the ALICE detector, pictured on this issue’s cover, is the largest pixel detector ever built and the first at the LHC to use monolithic active pixel sensors (p29). Next year, LHCb will also be equipped with an entirely new pixel tracker, the VELO, while ATLAS and CMS are developing advanced pixel trackers to be installed for future high-luminosity LHC operations (p36).

Silicon-pixel detectors developed for particle physics have also had a major impact on medical imaging, in particular via the CERN-led Medipix and Timepix collaborations (p23). Sticking with societal impact, this issue’s Viewpoint argues for an exascale computing facility based on the organisation of CERN (p49).

Elsewhere in our summer issue: collider neutrinos on the horizon (p7); particle accelerators meet gravitational waves (p18); reducing greenhouse gases in detectors (p20); exploring the Hubble tension (p51); reviews (p55); careers (p59); PIXEL and much more.

To sign up to the new-issue alert, please visit: PERFECT http://comms.iop.org/k/iop/cerncourier Exploring the Hubble tension To subscribe to the magazine, please visit: A CERN for climate change https://cerncourier.com/p/about-cern-courier Medical technologies

EDITOR: MATTHEW CHALMERS, CERN DIGITAL EDITION CREATED BY IOP PUBLISHING

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IN THIS ISSUE V o l u m e 61 N u m b e r 4 J u l y /A u g u s t 2 02 1 FASER Collaboration D Dominguez/KTTGROUP-PHO-TECH-2018-002-3 F Camallonga

New frontier Collider neutrinos on the Clinical dimensions CERN’s growing impact on Expanding views Cosmologist horizon at FASERν and SND@LHC. 7 medical technologies. 23 Licia Verde on the Hubble tension. 51

NeWs PeoPle

ANALYSIS ENERGY FRONTIERS FIELD NOTES CAREERS OBITUARIES Collider neutrinos Four top quarks seen at Accelerators meet From CERN to the Gerd-Jürgen Beyer • X boson feels the once • Gauge–boson gravitational waves environment • Vladimir Kukulin squeeze • Matter– polarisation • Hadron • Greening gaseous How skills developed in • Herbert Lengeler antimatter flips • Neutron formation • Charmed- detectors • Astroparticle high-energy physics can • Luc Pape • Jean Sacton. lifetime-puzzle • Latvia baryon lifetime. 15 theory in rude health. 18 be transferred to careers 65 joins CERN • Observatory in the environment nets PeV gamma rays. 7 industry. 59

FeAtures TSMC High-density wiring MEDTECH ALICE ATLAS, CMS AND LHCb HISTORY CERN’s impact on ALICE tracks State-of-the-art Tracking the rise Our new high-density wiring is a medical technology new territory tracking for high of pixel detectors Accelerators and their A look at the largest pixel luminosities Silicon pixel detectors modular option for the Bluefors side- detectors catalyse detector ever built and The tracking systems have blossomed into loading XLDsl dilution refrigerator innovative technology the first at the LHC to of ATLAS, CMS and LHCb beautiful creations that system that enables a large scale-up for medical applications. use monolithic active are undergoing complete have driven numerous of the experimental wiring, especially 23 pixel sensors. 29 overhauls. 36 discoveries. 39 for high-frequency signals. It is easy to install and to maintain. oPINIoN DePArtmeNts

VIEWPOINT INTERVIEW REVIEWS FROM THE EDITOR 5 ‘A CERN for Exploring the A relational take on NEWS DIGEST 13 climate change’ Hubble tension quantum mechanics APPOINTMENTS 60 Tim Palmer and Bjorn Licia Verde discusses Helgoland Particle & AWARDS

• ALICE-PHO-ITS-2021-001-32 Stevens argue for an the current tension in Detectors: Fundamentals RECRUITMENT 61 exascale computing the measurement of the and Application • Le On the cover: The outer facility based on the Hubble constant. 51 Neutrino de Majorana. 55 barrel of ALICE’s new inner BACKGROUND 70 CERN model. 49 tracking system installed in March. 29

CERN COURIER JULY/AUGUST 2021 3

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SHR Marvels of engineering and collaboration

he story of silicon pixel detectors is like that of an Nikhef ULTRA PRECISE HIGH VOLTAGE art form, describes our in-depth take on their history T (p39): with well-defined beginnings half a century ago, the technology has morphed into a vast array of spectacular SOURCE MEASURE UNIT creations. One, packing 10 million pixels into your pocket, is the smartphone camera; another is the newly installed, upgraded inner tracker for the ALICE detector adorning the DESIGNED FOR UNIVERSAL LABORATORY USE Matthew cover of this issue. Containing some 12.5 Gpixels, it is the Chalmers largest pixel detector ever built and the first at the LHC to use Editor monolithic active pixel sensors, or MAPS (p29). As well as disrupting photography, the silicon pixel detector – i n p a r a l l e l w it h it s c l o s e s i bl i n g t h e s i l i c o n-m i c r o s t r i p d e t e c t or, which will be explored in a future issue – revolutionised scientific imaging in the 1980s and 1990s. Charge-coupled devices (CCDs) tend to be the preferred option for astronomical applications, On point A LHCb VELO pixel module being assembled at Nikhef. most recently the 3.2 Gpixel optical camera for the Vera Rubin Observatory, while MAPS tend to be used for ultrafast imaging Beyond tracking such as studies of protein dynamics at X-ray free-electron lasers. Silicon-pixel detectors developed for particle physics have ALSO AVAILABLE It t o o k a fe w y e a r s t o m o v e a w a y f r o m g a s e o u s d r i f t c h a m b e r s for also had a major impact on medical imaging, for example AS NIM-DEVICE: t he h ig hest prec ision t r ac k i ng, but pa r t ic le physic ist s adopted via the CERN-led Medipix and Timepix collaborations (p23). silicon detectors for these applications in the early 1980s and Medipix chips recently enabled the first 3D colour X-rays never looked back. Successive generations of trackers based and, via CERN spin-out ADVACAM, are soon to be sent to the SK NHR on CCDs, MAPS and hybrid-pixel architectures have driven lunar surface to assess radiation levels ahead of NASA’s first A ER nu m e r o u s d i s c o v e r i e s. W it h t h e c o n s u m e r e l e c t r o n i c s i n d u s t r y c r e w e d fl i g ht t o t h e M o o n i n 50 y e a r s. A s pi n- o ut f r o mthePaul S? IC N H continuing to push chips to new levels of sophistication there S c h e r r e r I n s t it ut e c a l l e d DE C T R IS, m e a n w h i l e, h a s pio n e e r e d O ! I are also no sig ns t hat adv ances are slow ing dow n. the development of hybrid-pixel X-ray detectors for use in T

S The LHC detectors represent the state-of-the-art in particle- light sources, medicine and industry.

E t r a c k i n g a p pl i c a t i o n s, d e l i v e r i n g h i g h-g r a nu l a r it y d a t a a t s p e e d Sticking with the societal-impact theme, this issue’s U

Q Silicon-pixel under the most extreme operating conditions imaginable. The Viewpoint by two leading climate scientists (p49) argues for a detectors chips themselves are only one part of the story. They need to “CERN for climate change” – an exascale computing facility developed be integrated into modules with minimal material budget and based on the organisation of CERN that would allow better for particle installed with great precision in confined spaces, cooled, cabled quant ificat ion of climate models. Elsewhere in our summer W-IE-NE-R + ISEG PERFECT FOR physics have and read-out (p36). From R&D to construction, this complex issue: learn about the fascinating potential for particle accel- SUPPORT OFFICE AT CERN task, like that for the other LHC-experiment upgrades, is shared e r a t or s t o d e t e c t g r a v it a t i o n a l w a v e s ( p18), t h e d e t e c t i o n o f t h e also had a Dr. Dipl.-Phys. Erich Schaefer USE WITH NHR: between international collaborating laboratories and institutes, first collider-neutrino candidates (p7), the latest attempts to major impact Bat.: 13/R-023 | +41 75411 4301 | [email protected] QUALITY NIM CRATES with teams at CERN and across the world currently working address the Hubble tension (p51), efforts to reduce greenhouse on medical h a rd u nde r c h a l le ng i ng g lo b a l c i rc u m s t a nc e s to pre p a re t he i r gases in particle detectors (p20), reviews (p55), careers (p59) imaging detectors for Run 3 and beyond. and much more.

2 / 4 channels, 2 kV / 6 kV versions Reporting on international high-energy physics

CERN Courier is distributed Editor Laboratory correspondents Jefferson Laboratory SLAC National Technical illustrator General distribution Electronically switchable polarity to governments, institutes Matthew Chalmers Argonne National Kandice Carter Accelerator Laboratory A l ison Tove y Courrier Adressage, CERN, and laboratories affiliated Associate editor Laboratory JINR Dubna B St a rc hen ko Melinda Baker Advertising sales 1211 G e ne v a 23, S w it z erl a nd; with CERN, and to Mark Rayner Tom LeCompte KEK National Laboratory SNOLAB Samantha Kuula Tom Houlden e-mail courrier- 6 kV channel with electronically switchable modes: up to 2 kV/4 mA, 4 kV/3 mA or 6 kV/2 mA individual subscribers. Editorial assistant Brookhaven National Hajime Hikino TRIUMF Laboratory Recruitment sales [email protected] It is published six times Cr a ig Edw a rds Laboratory Ac h i m Fr a n z Lawrence Berkeley Marcello Pavan Chris Thomas per year. The views Astrowatch contributor Cornell University Laboratory Spencer K lei n Advertisement Published by CER N, 1211 High-precision / very low ripple and noise / high resolution expressed are not Merlin Kole D G Cassel Los Alamos National Lab Produced for CERN by production Kat ie Gr a ha m Geneva 23, Switzerland necessarily those of the E-mail DESY Laboratory Raja n Gupt a IOP Publishing Ltd Marketing and Tel +41 (0) 22 767 61 11 * CERN management. [email protected] Till Mundzeck NCSL Ken K i nger y Temple Circus, Temple circulation L au r a Gi l l h a m, USB / Ethernet interface Fermilab Kurt Nikhef Robert Fleischer Way, Bristol BS1 6HG, UK Jessica Pratten Printed by Wa r ners Advisory board Riesselmann Novosibirsk Institute Tel +4 4 (0)117 929 7481 (Midlands) plc, Bourne, * Peter Jenni, Forschungszentrum S Eidelman Advertising Lincolnshire, UK Integrated (ARM Linux server hardware) with onboard scripting Christine Sutton, Jülich Markus Buescher Orsay Laboratory Head of Media Jo A l len Tel +44 (0)117 930 1026 Claude Amsler, GSI Darmstadt I Peter Anne-Marie Lutz Head of Media (for UK/Europe display © 2021 CER N Philippe Bloch, IHEP, Beijing Lijun Guo PSI Laboratory P-R Kettle Business Development advertising) or +44 (0)117 ISSN 0304-288X 4.3“ TFT capacitive touch display (SHR) Roger For t y, IHEP, Serpukhov Saclay Laboratory Ed Jost 930 1164 (for recruitment M i ke L a mont, Yu Ry abov Elisabeth Locci Content and production advertising); e-mail *SHR-device only Joac h i m Kopp INFN Antonella Varaschin UK STFC Ja ne Bi n k s manager Rut h L eopold [email protected]

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NeutriNos Collider neutrinos on the horizon

Think “neutrino detector” and images of FASER Collaboration giant installations come to mind, neces- sary to compensate for the vanishingly small interaction probability of neutri- nos with matter. The extreme luminosity of proton–proton collisions at the LHC, however, produces a large neutrino flux in the forward direction, with energies 1000 μm leading to cross-sections high enough for neutrinos to be detected using a much more compact apparatus. In March the CERN research board New territory During its first phase of operation, of emulsion films and tungsten plates approved the Scattering and Neutrino A candidate SND@LHC is expected to collect an measuring 0.25 × 0.25 × 1.35 m and weigh- Detector (SND@LHC) for installation in collider-neutrino integrated luminosity of 150 fb–1, corre- ing 1.2 tonnes, FASERν is already under- an unused tunnel that links the LHC to the event from the sponding to more than 1000 high-energy going tests. The detector is positioned on SPS, 480 m downstream from the ATLAS FASERν pilot neutrino interactions. Since electron the beam-collision axis to maximise the experiment. Designed to detect neutri- detector in the plane neutrinos and antineutrinos are pre- neutrino flux, and should detect a total nos produced in a hitherto unexplored transverse to the dominantly produced by charmed- of around 20,000 muon neutrinos, 1300 pseudorapidity range (7.2 < η < 8.6), the beam direction, hadron decays in the pseudorapidity range electron neutrinos and 20 tau neutrinos experiment will complement and extend showing charged- explored, the experiment will enable the in an unexplored energy regime at the the physics reach of the other LHC exper- particle tracks gluon parton-density function to be con- TeV scale. This will allow measurements iments – in particular FASERν, which originating from strained in an unexplored region of very of the interaction cross-sections of all was approved last year. Construction of the neutrino small x. With projected statistical and neutrino flavours, provide constraints FASERν, which is located in an unused interaction point. systematic uncertainties of 30% and 22% on non-standard neutrino interactions,

service tunnel on the opposite side of in the ratio between νe and ντ, and about and improve measurements of proton ATLAS along the LHC beamline (covering 10% for both uncertainties in the ratio parton-density functions in certain

|η| > 9.1), was completed in March, while between νe and ντ at high energies, the phase-space regions. installation of SND@LHC is about to begin. Run-3 data will also provide unique tests Both experiments will be able to detect o f l e p t o n fl a v o u r u n i v e r s a l it y w it h n e ut ri- A FASER first neutrinos of all types, with SND@LHC nos, and have sensitivity in the search for In May, based on an analysis of pilot p o s it i o n e d o ff t h e b e a m l i n e t o d e t e ctneu- feebly interacting particles via scattering emulsion data taken in 2018 using a trinos produced at slightly larger angles. signatures in the detector target. target mass of just 10 kg, the FASERν Expected to commence data-taking dur- “The angular range that SND@LHC team reported the detection of the first ing LHC Run 3 in spring 2022, these latest will cover is currently unexplored,” says neutrino-interaction candidates, based additions to the LHC-experiment family SND@LHC spokesperson Giovanni De on a measured 2.7σ excess of a neutrino- a re poised to ma ke t he first obser v at ion Lellis. “And because a large fraction of like signal above muon-induced back- of collider neutrinos while opening new the neutrinos produced in this range come grounds. The result paves the way for searches for feebly interacting particles from the decays of particles made of heavy high-energy neutrino measurements and other new physics. quarks, these neutrinos can be used to at the LHC and future colliders, explains study heavy-quark particle production FASER co-spokesperson Jamie Boyd: “The Neutrinos galore in an angular range that the other LHC fi n a l de te c tor shou ld do muc h b e t ter – it SND@LHC will comprise 800 kg of tung- experiments can’t access. These meas- will be a hundred times bigger, be exposed sten plates interleaved with emulsion urements are relevant for the prediction to much more luminosity, have muon fi l m s a n d e l e c t r o n i c t r a c k e r pl a n e s b ased of very-high-energy neutrinos produced identification capability, and be able to o n s c i nt i l l a t i n g fi br e s. T h e e mu l s io n a c ts in cosmic-ray interactions, so the exper- link observed neutrino interactions in the as a vertex detector with micron reso- iment is also acting as a bridge between emulsion to the FASER spectrometer. It lution while the tracker provides a time accelerator and astroparticle physics.” is quite impressive that such a small and stamp, the two subdetectors acting as a FASERν is an addition to the Forward simple detector can detect neutrinos given sampling electromagnetic calorimeter. Search Experiment (FASER), which was that usual neutrino detectors have masses The target volume will be immediately approved in March 2019 to search for measured in kilotons.” followed by planes of scintillating bars light and weakly interacting long-lived interleaved with iron blocks serving as particles at solid angles beyond the reach Further reading a hadron calorimeter, followed down- of conventional collider detectors. Com- FASER Collab. 2021 arXiv:2105.06197. stream by a muon-identification system. prising a small and inexpensive stack SHiP Collab. 2020 arXiv:2002.08722.

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searches For new physics tems (those containing quarks from dif- “In the future we hope to discover 0 —0 3 ferent generations) can oscillate. K –K time-dependent CP violation in the — LHCb oscillations were observed in 1955, B0–B0 charm system, and the precision

‘ ’ 2 X boson feels the squeeze at NA64 oscillations in 1986 at the ARGUS exper- WS ) and luminosity expected from LHCb 4 0 —0 –1 3 iment at DESY, and Bs –Bs oscillations 10 /c upgrades I and II may make this pos- 5.4 fb 2 Recent measurements bolstering the O-201611-278-3 T N-PHO CER in 2006 by the CDF experiment at Fer- sible,” explains Nathan Jurik, a CERN

longstanding tension between the milab. Following the first evidence of ) fellow who worked on the analysis.

4 2 0 —0 experimental and theoretical values of charmed-meson oscillations (D –D ) /c The latest measurements of neutral 2 RS 2 the muon’s anomalous magnetic moment at Belle and BaBar in 2007, LHCb made 10 charm–meson oscillations follow hot on – [GeV

generated a buzz in the community (CERN t h e fi r s t s i n g l e- e x p e r i m e nt o b s e r v a t i o n 2 the heels of an updated LHCb measure-

m 0 —0 Courier May/June 2021 p5). Though with a confirming the process in 2012. Being ment of the Bs–Bs oscillation frequency m u c h l o w e r s i g n i fic a n c e, a s i m i l a r p u z z le relatively slow (more than 100 times the announced in April, based on the heavy 0 10 may also be emerging for the anomalous average lifetime of a D meson), the full 1 and light strange-beauty-meson mass

mag net ic moment of t he elect ron, a e. oscillation period cannot be observed. signal candidates per (4.5 MeV difference. The very high precision of 0 —0 Depending on which of two recent Instead, the collaboration looked for the Bs –Bs measurement provides one independent measurements of the small changes in the flavour mixture of the strongest constraints on phys- 0 1 fine-structure constant is used in of the D mesons as a function of the time 1 2 3 ics beyond the Standard Model. Using a the theoretical calculation of a – one at which they decay via the Kπ fi n a l s t a t e. 2 2 4 large sample of B0 → D– π+ decays, the new e m+ [GeV /c ] s s obtained at Berkeley in 2018 or the other On 4 June, during the 10th Interna- measurement improves upon the previ- at Kastler–Brossel Laboratory in Paris in tional Workshop on CHARM Physics, Bin flips LHCb used a Dalitz plot-based “bin-flip method” ous precision of the oscillation frequency 0 0 + – 0 —0 2020 – the Standard Model prediction the LHCb collaboration reported the analysis of D → Ks π π decays to infer the D – D mass difference, by a factor of two: ∆ms = 17.7683 ± 0.0051 stands 2.4σ higher or 1.6σ lower than the first observation of the mass difference where the axes of the plot are the squares of the invariant masses (stat) ± 0.0032 (sys) ps–1 which, when com- — best experimental value, respectively. between the D0–D 0 states, precisely of t wo pairs of the decay products. bined with previous LHCb measurements, Motivated by this inconsistency, the determining the frequency of the oscil- gives a value of 17.7656 ± 0.0057 ps–1. This NA64 collaboration at CERN set out to lations. The value represents one of the was marginally compatible with zero. By corresponds to an oscillation rate of investigate whether new physics - in the s m a l l e s t e v e r m a s s d i ffe r e n c e s b e t w e e n establishing a non-zero value with high around 3 × 1012 per second, the highest form of a lightweight “X boson” – might two particles: 6.4 × 10–6 eV, cor responding significance, the LHCb team was able to of all four meson systems. be influencing the electron’s behaviour. to an oscillation rate of around 1.5 × 109 show that the data are consistent with The generic X boson could be a sub- Exploration The NA64 set up is being used to search for new particles that might account for the electron per second. Until now, the measured t h e St a n d a r d M o d e l, w h i l e s i g n i ficantly Further reading G eV s c a l a r, p s e u d o s c a l a r, v e c t or or a x i a l- g–2 and ATOMKI anomalies. value of the mass-difference between improving limits on mixing-induced CP LHCb Collab. 2021 arXiv:2106.03744. — vector particle. Given experimental the underlying D0 and D0 eigenstates violation in the charm sector. LHCb Collab. 2021 arXiv:2104.04421. constraints on its decay modes involv- Sergei Gninenko. “But the fact that the NA64 team excluded a large range KEK ing Standard Model particles, it is pre- NA64 reached an experimental sen- of couplings, although at large values, NeutroN lifetime (J-PARC). The decay rate and the reaction s u m e d t o d e c a y pr e d o m i n a nt l y i n v i s i bl y, sitivity that is better than the current for a v e c t or-l i k e X 17. M or e r e c e nt l y, t h e y KEK tackles neutron- rate are determined by simultaneously for example into dark-sector particles. accuracy of the direct measurements of searched for a pseudoscalar X17, which detecting electrons from the neutron

NA64 searches for X bosons by directing ae, a nd of recent h ig h-prec ision meas- has a lifetime about half that of the vector lifetime puzzle decay and protons from the reaction 100 GeV electrons generated by the SPS urements of the fine-structure constant, version for the same coupling strength. 3He → 3H in a 1 m-long time-projection onto a target, and looking for missing is amazing.” Re-analysing a sample of approximately More than a century after its discovery, chamber containing diluted 3He, remov- energy in the detector via electron–nuclei I n a s e p a r a t e a n a l y s i s, t h e N A64 t e a m 8.4 × 1010 electrons-on-target collected the proton remains a source of intrigue, ing some of the systematic uncertainties scattering e–Z → e–ZX. carried out a model-independent search in 2017 and 2018 with 100 and 150 GeV its charge-radius and spin posing puzzles that affect previous beam methods. The Analysing data collected in 2016, 2017 for a particular pseudoscalar X boson electrons, respectively, the collaboration that are the focus of intense study (CERN experiment is still in its early stages, a n d 2018, c or r e s p o n d i n g t o a b o ut 3 × 1011 with a mass of around 17 MeV. Coupling has now excluded couplings in the range Courier May/June 2019 p38). But what of and while the first results have been + – –4 +15 electrons-on-target, the NA64 team to electrons and decaying into e e p a i r s, 2.1–3.2 × 10 for a 17 MeV X-boson. its mortal sibling, the neutron? In recent released – τn = 898 ± 10(stat)–18 (sys) s – found no evidence for such events. The the so-called “X17” has been proposed “We plan to further improve the sen- years, discrepancies between measure- the uncertainty is currently too large to result sets new bounds on the e–X inter- to explain an excess of e+e– pairs created sitivity to vector and pseudoscalar X17’s ments of the neutron lifetime using dif- draw conclusions. action strength and, as a result, on the during nuclear transitions of excited 8Be after long shutdown 2, and also try to ferent methods constitute a puzzle with “In the current situation, it is impor- 4 contributions of X bosons to ae: X bosons and He nuclei reported by the “ATOMKI” reconstruct the mass of X17, to be sure potential implications for cosmology and tant to verify the puzzle by experiments with a mass below 1 GeV could contribute experiment in Hungary since 2015 (CERN that if we see the signal it is the ATOMKI particle physics. The neutron lifetime in which different systematic errors at most between one part in 1015 and one Courier January/February 2020 p7). boson,” says Gninenko. determines the ratio of protons to neu- dominate,” says Kenji Mishima of KEK, part in 1013, depending on the X-boson The e-X17 coupling strength is con- trons at the beginning of big-bang nucle- Way to go The apparatus in which neutrons from J-PARC adding that further improvements in the type and mass. These contributions are strained by data: too large and the X17 Further reading osynthesis and thus affects the yields were clocked. statistical and systematic uncertainties

too small to explain the current anom- would contribute too much to ae; too small NA64 Collab. 2021 Phys. Rev. Lett. 126 211802. of light elements, and it is also used to are underway. “We think it will take two

aly in the electron’s anomalous mag- and the X17 would decay too rarely and too NA64 Collab. 2021 arXiv:2104.13342. determine the CKM matrix-element Vud results. Today, however, the average years to obtain a competitive result from n e t i c m o m e nt, s a y s N A64 s p o k e s p e r s o n f a r a w a y f r o m t h e AT OM K I t a r g e t. I n 2019, NA64 Collab. 2020 Eur. Phys. J. C 80 1159. in the Standard Model. neutron lifetime measured using the our e x per iment.” The neutron-lifetime puzzle stems bottle and beam methods, 879.4 ± 0.4 s Several new-physics scenarios have Flavour physics from measurements using two tech- and 888.0 ± 2.0 s, respectively, stand 8.5 s been proposed as solutions of the niques. The “bottle” method counts the (or 4σ) apart. neutron lifetime puzzle. These include Charmed matter–antimatter flips clocked by LHCb number of surviving ultra-cold neu- In an attempt to shed light on the exotic decay modes involving undetect- trons contained in a trap after a certain issue, a team at Japan’s KEK laboratory in able particles with a branching ratio of The ability of certain neutral mesons Only four nations of narrowly split mass eigen- instead via loops, such flavour-chang- period, while the “beam” method uses collaboration with Japanese universities about 1%, such as “mirror neutrons” or to oscillate between their matter and meson states that gain a relative phase as the ing neutral-current processes offer a the decay probability of the neutron has developed a new experimental setup. dark-sector particles. antimatter states at distinctly unworldly systems can wavefunction evolves, allowing quarks powerful test of the Standard Model and obtained from the ratio of the decay rate Similar to the beam method, it compares rates is a spectacular feature of quan- and antiquarks to be interchanged at a a sensitive probe of physics beyond it. t o a n i n c i d e nt n e ut r o n flu x . B a c k i n t he the decay rate to the reaction rate of neu- Further reading oscillate tum mechanics. The phenomenon arises rate that depends on the mass differ- Predicted by Gell-Mann and Pais in 1990s, the methods were too imprecise trons in a pulsed beam from the Japan K Hirota et al. 2020 Prog. Theor. Exp. Phys. when the states are orthogonal combi- e n c e. For bi d d e n a t t r e e l e v e l, pr o c e e d i n g t h e 1950 s, o n l y fo u r k n o w n m e s o n s y s- t o w or r y a b o ut d i ffe r e n c e s b e t w e e n t he Proton Accelerator Research Complex 123C02.

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cr AstrowAtch L A EN Mountain observatory nets PeV gamma rays

n 1 April representatives o CER CER--1--1 economy and well-eing o or soci- and the Replic o atvia gathered in eties said atvian prime minister Recent years have seen rapid growth Nature a virtal ceremony to sign an agree- Krišjānis Kariņš. in high-energy gamma-ray astron- ment admitting atvia as an Associate As an Associate Memer tate omy, with the first measurement of TeV Memer tate atvia will e entitled to appoint rep- p h o t o n s f r o m g a m m a-r a y b u r s t s b y t h e atvia which is the third o the resentatives to attend meetings o the MAGIC telescope (CERN Courier January/ altic tates to oin CER in recent CER Concil and inance Committee February 2020 p10) and the first detec- ye a r s a f te r L it hua n i a a nd E s ton i a, fi r s t Its nationals will be eligible for staff t io n o f g a m m a r a y s w it h e n e r g ie s a b o v e ecame involved with CER activities positions ellowships and stdentships 100 TeV by the HAWC observatory (CERN in the early 1s atvian researchers and its indstries will e entitled to Courier July/August 2020 p12). have since participated in many CER id or CER contracts increasing Now, the Large High Altitude Air proects inclding contritions to the opportnities or collaoration in S h o w e r O b s e r v a t or y (L H A A S O) i n C h i n a CM hadron calorimeter and more advanced technologies has increased the energy scale at which recently participation in the tre e are delighted to welcome atvia the universe has been observed by a Circlar Collider stdy as a new Associate Memer tate said further order of magnitude. The recent As we ecome CER’s newest CER irector-General aiola Gianotti LHAASO detection provides the first Associate Memer tate we loo or- he present agreement contrites to c lea r e v idence of t he presence of g a lac- ward to enhancing or contrition strengthening the ties etween CER tic “pevatrons”: sources in the Milky to the Organization’s major scientifi c and Latvia, thereby off ering opportu- Wa y c a p a bl e o f a c c e l e r a t i n g pr o t o n s a n d endeavors as well as to investing nities or the rther growth o particle electrons to PeV energies. Although PeV the unparalleled scientifi c and tech- S Lativan prime minister Krišjānis Kariņš physics in atvia throgh partnership c o s m i c r a y s a r e k n o w n t o e x i s t, m a g n e t i c nological ecellence gained y this and CERN irectoreneral abiola ianotti on the occasion of in research technological development fields pervading the universe perturb memership in rther ilding the the reote signature of the agreeent. and edcation t h e i r d i r e c t i o n a n d t h e r e for e d o n o t a l l o w t h e i r or i g i n t o b e t r a c e d. T h e g a m m a r a y s produced by such cosmic-rays, on the o t h e r h a n d, p oi nt d i r e c t l y t o t h e i r s o u r c e.

High Voltage Power Solutions Wide field of view LHAASO is located in the mountains of the Sichuan province of China and High-energy vista The universe seen using photons with energies exceeding 100 TeV by LHAASO. A total offers a wide field of view to study both of 12 sources, including the Crab nebula, can be observed along the galactic plane, indicating that all lie high-energy cosmic and gamma rays. within the Milky Way. Once completed, the observatory will c o nt a i n a w a t e r C h e r e n k o v d e t e c t or w it h Of specific interest is t he sible sources within them. The sizes of Up to 500kVDC output a t o t a l a r e a o f a b o ut 78,000 m2, 18 w i d e- the emission regions exceed the angular fie l d- o f-v i e w C h e r e n k o v t e l e s c o p e s a nd source responsible for t he resolution of LHAASO, however, indi- a 1 km2 a r r ay of more t h a n 5000 sc i nt i l- cating that emission takes place over lator-based electromagnetic detectors photon w it h t he hig hest large scales. Of specific interest is the with power to 200kW (EDs). Finally, more than 1000 under- source responsible for the photon with ground water Cherenkov tanks (the MDs) energ y, 1.4 PeV the highest energy, 1.4 PeV. This came XP Power offers one of the widest ranges of high voltage power are placed over the grid to detect muons. from a region containing both a super- T h e l a t t e r t w o d e t e c t or s, o f w h ic h o n l y nova remnant as well as a star-forming solutions, backed with exceptional technical and customer half were finished during data-taking located across the galactic plane (see c lu s t e r, b o t h o f w h i c h a r e pr i m e t h e or e t- support, and a three year warranty. for t h i s s t u d y, a r e u s e d t o d i r e c t l y d e t e c t image above). This distribution is ical candidates for hadronic pev at rons. the showers produced when high-energy expected, since gamma rays at such particles interact with the Earth’s atmos- energies have a high cross-section for Tip of the iceberg p h e r e. T h e E D s d e t e c t t h e s h o w e r pr o fi l e pair production with the cosmic micro- More detailed spectrometry as well as Output voltages from 100VDC to 500kVDC and incoming angle, using charge and w a v e b a c k g r o u n d a n d t h e r e for e t h e u n i- m or p h ol o g i c a l m e a s u r e m e nt s, i n w h i c h Output power from 0.5W to 200kW t i m i n g i n for m a t i o n o f t h e d e t e c t or a r r a y, v e r s e s t a r t s t o b e c o m e o p a q u e a t e n e r g i e s the differences in emission intensity while the MDs are used to distinguish exceeding tens to hundreds of TeV, leav- throughout the sources are measured, Input ranges including DC, single & three phase AC h a d r o n ic s h o w e r s f r o m t h e e l e c t r o m a g- i n g o n l y s o u r c e s w it h i n o u r g a l a x y v i s i- could allow the sources of > 100 TeV Programmable, proportional, local control & various digital options netic showers produced by high-energy bl e. O f t h e 1 2 pr e s e nt e d s o u r c e s, o n l y t h e gamma rays to be identified in the next g a m m a r a y s. T h a n k s t o b o t h it s l a r g e s i z e Crab nebula can be directly confirmed. one or two years, say the authors. Fur- Low noise, accurate and reliable high voltage for critical, long term applications and the MDs, LHAASO will ultimately This substantiates the pulsar-wind neb- t h e r m or e, a s t h e c u r r e nt 1 2 s o u r c e s w e r e be two orders of magnitude more sen- ulae as a source in which electrons are v isible using only one year of data from For more information about our products visitwww.xppower.com or email us at [email protected] sitive at 100 TeV than the HAWC facility a c c e l e r a t e d b e y o n d P eV e n e r g i e s, w h i c h half the detector, it is clear that LHAASO in Mexico, the previous most sensitive in turn are responsible for the gamma is only seeing the tip of iceberg when it detector of t his t y pe. rays through inverse Compton scattering. comes to high-energy gamma rays. The measurements reported by the The origin of the other photons Chinese-led international LHAASO col- remains unknown as the observed Further reading laboration reveal a total of 12 sources emission regions contain several pos- Z Cao et al. 2021 Nature 594 33.

1 CERN COURIER JULY/AUGUST 2021 CERN COURIER JULY/AUGUST 2021 11

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that is then converted by Leptoquarks and H → μμ connected to five new detect ion Standard Model interactions A ndreas Crivellin (CERN), Dario units of t he A RC A telescope. LUX/DESY (including sphalerons) into Müller (PSI) and Francesco Once complete, t he detector w ill a bar yon asy mmet r y. By Sat ur nino (Ber n) have show n for m an ar ray of more t han 200 generalising standard “freeze- t hat leptoquarks (LQs) are not detection units – each 700 m tall out” leptogenesis, such that all only well motivated by hints and comprising 18 sensor modules conserved charges at the time of of lepton-flavour-universality to reg ister t he faint flashes of light leptogenesis are allowed to take violation (CERN Courier May/ generated by neutrino interactions An electron bunch (centre) surfs on arbitrary values, CERN’s Valerie June 2021 p17) but t hat t here may in the pitch-black abyss of the a plasma wave of electrons (white) Domcke, Kyohei Mukaida, Kai also be a LQ lin k bet ween t he Mediterranean Sea. Together driven by a laser pulse (red). Schmitz and colleagues have muon g–2 anomaly and ongoing w it h its sister detector, ORC A, recently made an important measurements of the decay of the located offshore from Toulon, Optimal wakefield acceleration contribution to the theory that Higgs boson to a pair of muons France, the KM3NeT telescopes In a step towards the continuous lowers the possible mass range (arXiv:2008.02643, accepted in will identify astrophysical sources operation necessary for of the RHNs down to a few Phys. Rev. Lett.). Should LQs prove of high-energy cosmic neutrinos applications, physicists at 100 TeV, actively “washing in” to be the true explanation of the and st udy neut rino oscil lat ions. DESY and the University of the observed baryon asymmetry 4.2σ tension in t he muon g–2 With a total of six ARCA detection When Compromise is Not an Option. Hamburg have narrowed the (arXiv:2011.09347). repor ted by Fer milab in April units now joining si x ORC A units energy distribution of electron (CERN Courier May/June 2021 p7), in taking data, KM3NeT now bunches emerging from a Looking for GW lensing the effect of LQs should also be has comparable sensitivity to High-Performance Digitizers for plasma-wakefield accelerator. LIGO and Virgo have published t he observable in future precision itspredecessor telescope in the Plasma accelerators can have first searc h for t he g rav itat ional measurements of H → μ+μ–. The northern hemisphere, ANTARES.

gradients 1000 times higher than lensing of gravitational waves first ev idence for t his decay w as M Brice/CERN Big Physics Applications conventional radio-frequency (GWs). Just as light bends around repor ted by CMS and ATL AS in cavities, but have thus far only massive astronomical objects such August last year, with signal Digitizers from Teledyne SP Devices utilize patented been operated on a shot-by-shot as stars, black holes and galaxies, strengths with respect to the basis. Using the LUX test facility causing magnification, multiple Standard Model of 1.2 ± 0.4 and calibration technology, the latest data converters, and at Hamburg, the team employed 1.2 ± 0.6, respect ively (CERN Courier state-of-the-art FPGAs in order to achieve an unrivaled a new type of hydrogen cell, with September/October 2020 p7). nitrogen added to a 10 mm region Sergio Arguedas Cuendis adjusts the R Buscicchio R combination of high resolution and sampling rate. Their where t he bunc h is for med. France and Japan launch ILA NCE RADES detector. versatility makes them ideal for applications such as Artificial-intelligence techniques On 1 April, t he Universit y of Tok yo were then used to optimise the and France’s Cent re Nat ional de RADES reports results beam position monitoring, Thomson scattering plasma concentration and density of the la Rec herc he Scient ifique (CNRS) The Relic Axion Dark-Matter diagnostics, and more. gases and the energy and focus of established the International Exploratory Setup (RADES) the laser that drives the plasma Artist’s impression of lensed Laboratory for Astrophysics, haloscope at CERN has reported wave on which the bunch surfs gravitational waves. Neutrino and Cosmology the results of its first search for Supported features include: (see figure above). As a result of Experiments (ILANCE) in Kashiwa, axions (arXiv:2104.13798). The this “optimal beam loading”, the images and “Einstein rings”, GWs Greater Tok yo. CNRS’s sevent h detector was installed inside one • Up to 10 GSPS sampling rate with 14 bits resolution electrons reach the same energy can also be lensed by intervening international research lab in Japan, of the CAST experiment’s dipole regardless of their position along objects. Possible sig nals include IL ANCE w ill par t icipate in t he mag net bores in 2018. While • Open FPGA for custom real-time signal processing the wave (Phys. Rev. Lett. 126 an overall amplificat ion of t he Super- and Hyper-Kamiokande CAST seeks to use the inverse 104801 and 174801). waves, making binary-merger neutrino experiments, the Prima koff effect to conver t solar • Multiple form factors including MTCA.4, PXIe, and PCIe signals appear to come from LiteBIRD cosmic-microwave- a x ions into X-rays, R A DES seeks to Wash-in leptogenesis closer and higher-mass sources background experiment, the observe electric-field oscillations • Multi-channel synchronization capabilities Early attempts to explain the than they really do; “repeated” KAGRA gravitational-wave in a resonant cavity – evidence, origin of the baryon asymmetry events separated by minutes, detector, t he ATL AS e x periment potentially, for the presence of • White Rabbit synchronization (MTCA.4 only) of the universe using CP-violating months or years; or a beating and studies for the International axions in the dark-matter halo • Peer-to-peer streaming to GPU (PCIe only) decays of massive GUT particles pattern caused by tiny time delays Linear Collider. The lab w ill be of the Milky Way (CERN Courier were spoiled by electroweak (“microlensing”). As expected, directed by Michel Gonin and M a rc h/Apr i l 2021 p25). The dete c tor • Application-specific firmware shortens design time “sphaleron” processes that given current sensitivities, no Nobel-laureate Takaaki Kajita. pushes this technique to search for non-perturbatively wash out ev idence for lensing w as found. axions with a relatively high axion baryon-plus-lepton number. In t he f ut ure, however, t he effect Sicilian neutrino upgrade mass of 34.67 µeV by subdiv iding This prompted an alternative could help locate merging black During a week-long campaign its cavity into several cells, thereby explanation called leptogenesis, holes, estimate the population in April, the KM3NeT neutrino offset t ing t he lower detect ion during which the CP-violating of primordial and intermediate- observatory upgraded its seabed probability of the smaller cavities decays of hypothesised right- mass black holes, measure the in frast r uct ure near Sicily. A hub needed to probe higher masses. handed neutrinos (RHNs) speed of GWs, and test general for power distribution and data The team found no evidence for create a lepton asymmetry relativity (arXiv:2105.06384). transmission was installed and a x ions in 100 hours of data. Learn more on our website www.spdevices.com CERN COURIER JULY/AUGUST 2021 13

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Reports from the Large Hadron Collider experiments ATLAS Four top quarks seen at once

The production of four top quarks is an ATLAS extremely rare event at the LHC, with ATLAS data tttt– – an expected cross section five orders of –1 – – 104 √s = 13 TeV, 139 fb ttW ttZ magnitude below the production of a top- SR ttH– Q mis-id post-fit quark pair. With the heaviest elementary mat. conv. HF e 3 particle in the Standard Model produced 10 low mγ* HF μ four times in the final state, it is also others ttt uncertainty one of the most spectacular processes 2 accessible at the LHC. By combining 10 two analyses, the ATLAS collaboration

has uncovered the first strong evidence events / 0.1 10 to support the existence of this unique event topology with sensitivity to theo- ries beyond the Standard Model (BSM). 1 As a result of its large mass, the top Four-top candidate One top quark decays to a muon (red), one to an electron (green) quark plays a special role in numerous 10–1 BSM theories, and many of these theories and two decay hadronically. Missing predict an increase in the four-top-quark transverse momentum is indicated by a 1.0 production cross section. In particular, dotted line and the blue cones are b-jets.

four-top-quark production is the only data / pred. 0 process that could probe potentially searches for events with one lepton or –0.8 –0.6 –0.4 –0.2 0 0.2 0.4 0.6 0.8 1.0 a n o m a l o u s e ffe c t i v e fo u r-h e a v y-fe r m i o n BDT score two oppositely-charged leptons. This operators. The cross section is also sensi- selection retains 57% of the possible tive to the value of the top-quark Yukawa Fig. 1. Distribution of the multivariate discriminant score for four-top-quark final states, but suffers coupling, as a result of contributions data events (black dots) together with the background and signal from a large background from top-quark mediated by Higgs bosons. However, prediction (stacked histograms) for the analysis using events pairs produced in association with many until now, four-top-quark production with two leptons with the same electric charge or three leptons. jets, some of which are consistent with has not been observed, in part because The lower panel shows the ratio of the data to the total prediction, originating from b-quarks (b-jets). This of its tiny production rate, and in part where the band represents the total uncertainty. background is difficult to model and was because the experimental signature of determined using data control samples. this process is very complex, requiring up ATLAS preliminary √s = 13 TeV, 139 fb–1 To better isolate the signal from the back- to 12 particles to be reconstructed from tot. tttt– – ground, multivariate discriminants were stat. the top-quark decays. The search is also tot. ( stat., syst. ) obs. sig. trained in both analyses using distinct a ffe c t e d b y b a c k g r o u n d s o u r c e s i nkie- features of the signal, such as the number 2.2 1.6+ ( 0.7+ , 1.5+ ) 1.9 σ A succesful collaboration – particle matic regions that are at the limit of the 1L/2LOS 1.2− 0.7− 1.0− of b-jets and the kinematic properties of domain of validity of the simulations. t h e r e c o n s t r u c t e d p a r t i c l e s (s e e fi g u r e 1).

Despite these challenges, the ATLAS 0.8+ 0.4+ 0.7+ Results from the two studies were 2LSS/3L 2.0 0.6− ( 0.4− , 0.4− ) 4.3 σ collaboration has recently released two combined, leading to a four-top-quark accelerators and vacuum technology studies of four-top-quark production cross-section measurement at 13 TeV 2.0 0.8+ ( 0.4+ , 0.7+ ) 4.7 +7 using its full Run-2 data sample. The combined 0.6− 0.4− 0.5− σ of 25–6 fb, which is consistent with the first study searches for events with two Standard Model prediction of 12.0 ± 2.4 fb Pfei er Vacuum is proud to have been a supplier of innovative and customized vacuum solutions to the particle accelerator leptons (electrons or muons) with the within 2.0σ (s e e fi g u r e 2). T h e s t at i s t ic a l community for more than 50 years. Our complete product portfolio for vacuum technology, our focus on competent and 024 6 810 SM same electric charge or with three lep- –– –– s i g n i fic a n c e o f t h e s i g n a l c or r e s p o n dsto specialized advice supported by robust and reliable service, makes Pfei er Vacuum the partner of choice for the analytical best-fit μ = σtttt/σtttt tons. This selection corresponds to only 4.7σ, providing strong evidence for this and research communities worldwide. 13% of all possible four-top-quark final Fig. 2. Measurements of the four-top-quark cross section over its process, close to the observation threshold states, but is contaminated by only a small Standard Model prediction (μ) at 13 TeV, for the analysis using of 5σ. LHC Run-3 data, possibly at a higher ■ Pumps for vacuum generation down to UHV background, mainly from the produc- events with only one lepton or two oppositely-charged leptons centre-of-mass energy, will allow ATLAS ■ Vacuum measurement and analysis equipment tion of a top-quark pair with a W, Z or (1L/2LOS), for the analysis with two leptons with the same electric to verify whether the larger measured ■ Leak detectors and integrity test systems Higgs boson and additional jets, or from charge or three leptons (2LSS/3L), and for the combination. cross section relative to the prediction is ■ Chambers, components and valves events with one lepton with misiden- confirmed or not. ■ Pumping stations and customized solutions tified electric charge or a “fake” lepton theoretical predictions; the rates of the that doesn’t correspond to a W or Z boson m o s t d i ffic u l t o n e s w e r e m e a s u r e d u sing Further reading decay. Background processes were pri- control samples with similar properties ATLAS Collab. 2020 Eur. Phys. J. C 80 1085. Are you looking for a perfect vacuum solution? Please contact us: marily simulated using the best available to the signal events. The second study ATLAS Collab. 2021 ATLAS-CONF-2021-013. Pfeiffer Vacuum (Schweiz) AG · T +41 44 444 22 55 · F +41 44 444 22 66 · [email protected] www.pfeiffer-vacuum.com CERN COURIER JULY/AUGUST 2021 15

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CMS in the event portion perpendicular to a a baryon-to-meson enhancement that jet cone. This allows physicists to look ALICE qualitatively resembles the observations p–Pb √s NN = 5.02 TeV “under the peak” to reveal more about inclusive i n P b –P b c ol l i s i o n s. T h e n e w s t u d y c l a r i- Gauge–boson polarisation observed in WZ production 1.0 Jet: anti-kT, R = 0.4, |ηjet| < 0.35 0 perp. cone its origin. The latest study focuses on the |ηV | < 0.75 fies that the high rise of the ratio is asso- 0 0 At the collision energies of the LHC, –1 –1 neutral and weakly decaying Λ baryon V s in jets R(V , jet) < 0.4 ciated with the soft part of the events CMS preliminary 137.2 fb (13 TeV) CMS preliminary 137.2 fb (13 TeV) 0 S 0.6 0 ch diboson processes have relatively high and K S meson – particles often known pT, jet > 10 GeV (regions where no jet with more than production cross sections and often pro- c ol l e c t i v e l y a s V 0 d u e t o t h e i r d e c a y p a r- ch p = 10 GeV is produced) and brings the eee pT, jet > 20 GeV T d u c e r e l a t i v e l y c l e a n fi n a l s t a t e s w it h t wo ticles forming a “V” within a detector. – fi r s t q u a nt it a t i v e g u id a n c e for m o d e l l ing + Λ )/2K POWHEG 0.5 or more charged leptons. Consequently, ee T h e A L IC E d e t e c t or c a n r e c o n s t r u c t t h e s e t h e b a r y o n-t o -m e s o n e n h a n c e m e nt w it h μ (NLO QCD+LO EWK) 0.4 ( Λ multilepton final states resulting from decaying particles reliably even at high a n a d d it i o n a l i m p or t a nt c o n s t r a i nt – t h e MATRIX W diboson processes are powerful signa- μμe (NNLO QCD+LO EWK) f O momenta via invariant-mass analysis a b s e n c e o f t h e j e t. M or e o v e r, fi n d i n g t h a t tures to study the properties of the elec- MATRIX using the charged-particle tracks seen the “within-jet” ratio is similar in pp and μμμ 0.2 PYTHIA8 t r o w e a k s e c t or o f t h e St a n d a r d M o d e l. I n (NNLO QCDxNLO EWK) in t he detectors. p–Pb collisions, while the “out-of-jet” statistical observed, 68% CL 0 particular, WZ production is sensitive to observed, 95% CL best fit The pa r t ic les a sso c iate d w it h t he jet s r a t i o s h o w s l a r g e r v a lu e s i n p –P b t h a n i n combined systematic 0 246810 12 observed, 99% CL Powheg+Pythia the strength of the triple gauge coupling luminosity show the typical ratio known from the p p c ol l i s io n s, g i v e s e v e n m or e t o p o n d e r 0 pT [GeV] that characterises the WWZ vertex, which 0 0.1 0.2 0.3 0.4 high momentum tail of the inclusive about the possible origin of the effect in derives from the non-Abelian nature of 40 50 60 W W baryon-to-meson distribution – essen- Fig. 1. The enhancement in the production of Λ baryons with relation to an expanding strongly inter- σ(pp → WZ) [pb] f – f RL 0 the electroweak sector. Additionally, tially no enhancement – and similar respect to KS mesons at intermediate transverse momenta acting system. Future measurements as the Higgs mechanism is responsi- Fig. 1. Left: the measured WZ production cross section in various final states compared to predictions at values were found in both pp and p–Pb (orange circles) is largely due to V 0-particle decays found outside involving multi-strange baryons may ble for the appearance of longitudinally different orders in perturbative QCD and electroweak theory (EWK). Right: measured polarisation fractions collisions, consistent with simulations charged-particle jets (open circles), and is not seen for the shed further light on this question. polarised gauge bosons, studying W and for the W boson in WZ production, compared with the Standard Model expectation (◊). of hard pp collisions using PYTHIA 8 V 0-particle decays found inside them (red and open triangles). Z boson polarisation indirectly probes the (see figure 1). By contrast, the particles The dashed curves represent PYTHIA 8 simulations of pp collisions Further reading

v alidit y of t he Higgs mec hanism. fit t i n g s c h e m e p a i d o ff, a s t h e fi n a l result and fo, which correspond to the proportion found away from jets do indeed show outside (black) and inside jets (red). ALICE Collab. 2021 arXiv:2105.04890. A recent result from the CMS collab- has a relative uncertainty of 4%, down of bosons in the left, right and longitudi- oration uses the full power of the data from the 6% obtained in past iterations nally polarised states in WZ production. LHCb taken during Run 2 of the LHC to learn of the measurement. The results are The measured polarisation fractions as much as possible from WZ production all consistent with state-of-the-art are consistent within 1σ with the Stand- New charmed-baryon lifetime hierarchy cast in stone in the decay channels involving three t heoret ical predict ions (fig ure 1, lef t). a r d M o d e l pr e d i c t i o n s (fi g u r e 1, r i g ht), i n c h a r g e d l e p t o n s (e l e c t r o n s or m u o n s). T h e A highlight of the analysis is the study accordance with our knowledge of the W h i c h c h a r m e d b a r y o n d e c a y s fi r s t? T h e The charmed-baryon lifetime puzzle results include the first observation at of the polarisation of both the W and the Z electroweak spontaneous symmetry LHCb collaboration recently challenged has now been resolved by a new meas- 0 0 + + any experiment of longitudinally polar- b o s o n s i n t h e h e l ic it y f r a m e, u s i n g m i s s- breaking mechanism. The significance the received wisdom of fixed-target Ωc Ξc Λc Ξc urement from LHCb using a much larger PDG 0 0 ised W bosons in diboson product ion. ing transverse energy as a proxy for the for the presence of longitudinally polar- e x p e r i m e nt s b y a l m o s t q u a d r u pl i n g t h e (2018) sample of Ωc and Ξc baryons produced Reconstruction and event selection transverse momentum of the neutrino in ised vector bosons is measured to be 5.6 m e a s u r e d l i fe t i m e o f t h e d o u bl y s t r a n g e directly in proton–proton collisions. σ 0 + 0 + The results 0 Ξc Λc Ωc Ξc we re opt i m i s e d to re duc e c ont r i but ion s the W decay. This choice, coupled with the for the W boson and well beyond 5σ for Ωc (CERN Courier July/August 2018 p11). LHCb SL Both particles are detected in the final include – – + from processes with “non-isolated” precisely measured four-momenta of the Z-b o s o n pr o d u c t i o n. T h e s e n e w s t u d i e s Now, a follow-up measurement by the (2018/19) 0 s t a t e pK K π . T h e m e a s u r e m e nt i s m a d e Ξc 0 electrons and muons produced in hadron the first three leptons and the requirement that pave the way for future measurements c ol l a b or a t io n c o n fi r m s t h e r e v i s e d h ier- Ωc relative to the lifetime distribution of LHCb Prompt decays – traditionally one of the primary W boson be on-shell, allows both the W of doubly polarised diboson cross sec- archy, offering valuable input to theo- t h e c h a r m e d m e s o n D 0 v i a D 0 → K+K–π+π– observation of (2021) LHCb comb. sources of experimental uncertainty in longitudinally and Z momenta to be fully reconstructed. tions, including the challenging doubly ret ical models of t he decays. decays, in order to control systematic such measurements. The total produc- The angle between the W (Z) boson and longitudinal polarisation mode in WW, Ground-state baryons containing uncertainties. Taking advantage of the polarised + + tion cross section for WZ production the (negatively) charged lepton origi- WZ or ZZ product ion. a charm quark (c), such as Λc (udc), Ξc 0 100 200 300 400 500 per for mance and detailed understand- W bosons 0 0 was measured with a simultaneous fit nat ing from its decay is t hen computed. (usc), Ξc (d s c) a n d Ωc (s s c), d e c a y v i a t h e lifetime [fs] ing of the LHCb detector, the lifetimes 0 0 to the signal-enriched region and three in diboson The resulting distributions are fitted to Further reading weak interaction. The ordering of their of the Ωc and Ξc baryons are found to 0 d i ffe r e nt c o nt r ol r e g io n s. T h i s e l a b or a te production extract the polarisation fractions fR, fL, CMS Collab. 2021 CMS-PAS-SMP-20-014. lifetimes has long been thought to be Fig. 1. Measurements of charmed-baryon lifetimes from be τ(Ωc) = 276.5 ± 13.4 (stat) ± 4.5 (syst) fs + + 0 0 0 τ(Ξ c) > τ(Λc) > τ(Ξ c ) > τ(Ωc ), based on fixed-target experiments (PDG 2018) and from the LHCb and τ(Ξc) = 148.0 ± 2.3 (stat) ± 2.2 (syst) fs, ALICE m e a s u r e m e nt s f r o m fi x e d-t a r g e t e x p er- experiment using charmed baryons produced from semileptonic respectively, where the precision of 0 i m e nt s n e a rl y 20 y e a r s a g o. Ho w e v e r, t h e b-decays (LHCb SL) and now from proton–proton collisions directly the Ωc lifetime is improved by a fac- situation changed dramatically in 2018 (LHCb Prompt), showing the progression in our understanding. tor of two compared to the semilep- Hadron format ion differs outside of jets when LHCb joined the game using a sam- tonic measurement. The new results 0 ple of Ωc b a r y o n s o b t a i n e d f r o m b o t t o m- an expansion in powers of 1/m c, where are consistent with the previous LHCb

The production of different types of b y c o m p a r i n g t h e pr o d u c t i o n o f s t r a n g e that it exceeds unity, implying the pro- baryon semileptonic decays. That LHCb mc i s t h e c o n s t it u e nt c h a r m– q u a r k m a s s. measurements, and hence establish the 0 3 hadrons provides insights into one of neutral baryons and mesons inside and duction of more baryons than mesons. study measured the Ωc lifetime to be Calculations up to order 1/mc imply a n e w l i fe t i m e h ie r a rc h y. C o m bi n i n g t h i s the most fundamental transitions in outside of c harged-par t icle jets. T h e r i s e o f t h e r a t i o h a s b e e n a s s o c i a t e d n e a rl y fo u r t i m e s l a r g e r t h a n pr e v i o u s l y lifetime hierarchy consistent with the measurement with the previous LHCb 0 nature – the “hadronisation” of highly One of the ways to contrast baryon with either hadron formation from the measured, transforming the hierarchy original fixed-target measurements, results gives τ(Ωc) = 274.5 ± 12.4 fs and + 0 + 0 0 energetic partons into hadrons with and meson production is to analyse the recombination of two or three quarks, or into τ(Ξc) > τ(Ωc) > τ(Λc) > τ(Ξc). One year though only qualitatively. Attempts at τ(Ξc ) = 152.0 ± 2.0 fs, the most precise confined colour charge. To understand ratio of their momentum distributions. the migration of the heavier baryons to later, LHCb significantly improved the higher-order calculations up to order charm-baryon lifetimes to date. The 4 how this transition takes place we have This has been done in most of the col- higher momenta by the strong all-par- precisions of the lifetimes of the other 1/mc, however, cannot accommodate the newly confirmed lifetime hierarchy to rely on measurements, and measure- lision systems, but the comparison is ticle “radial” flow associated with the three charmed baryons using the same ol d h i e r a r c h y, b ut c a n e x pl a i n t h e n e w o n e will help improve our knowledge of ment-driven modelling. This is because particularly interesting in heavy-ion A recent production and expansion of a quark– method, also finding the lifetime of the i f a s u p pr e s s i o n f a c t or t o t h e c o n s t r u c t i v e QCD dynamics in charm hadrons, and 0 the strong interaction processes that collisions, where a large baryon-to- result adds an gluon plasma. Ξc baryon to be larger than the world- Pauli-interference and semileptonic provides a crucial input to calibrate govern hadronisation are characterised meson enhancement is often referred e x t r a t w i st The ALICE collaboration has studied average v alue by about 3σ (fig ure 1). terms is written in. The origin of the theoretical calculations. by a scale given by the typical size of to as the “baryon anomaly”. A char- baryon-to-meson ratios extensively. A T h e c or r e s p o n d i n g t h e or e t i c a l c a lc u- suppression factor is still unknown, to the study hadrons – about 1 fm – and cannot be acteristic maximum at intermediate recent result adds an extra twist to the lations are challenging. In the charm but probably due to even higher order Further reading calculated with perturbative techniques. transverse momenta (1–5 GeV) is found of strange study of strange baryons and mesons sector, an effective theory of heavy- effects. An independent measurement LHCb Collab. 2021 LHCb-PAPER-2021-021. The ALICE collaboration has recently per- i n a l l s y s t e m s, b ut i n P b –P b c ol l i s io n s t h e baryons and by studying the ratios in two parts of quark expansion is taken to calculate was therefore needed to confirm the LHCb Collab. 2019 LHCb-PAPER-2019-008. s formed a novel study of hadronisation ratio is strongly increased, to the extent mesons the events separately – inside jets and lifetimes of charmed baryons through experimental situation. LHCb Collab. 2018 LHCb-PAPER-2018-028.

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Resonant responses Extraordinarily, shop work SRGW2021 RIES A SRF cavity might act as a resonant bar NOTES Since the invention of the synchrotron, storage rings or serve as a Gertsenshtein converter, in storage rings have been afflicted by could act not both cases converting a graviton into a difficult-to-control resonance effects only as GW photon in the presence of a strong back- Reports from events, conferences and meetings that degrade beam quality. When a detectors, ground magnetic field and yielding a new ring is commissioned, accelerator but also as direct electromagnetic signal – similar Topical workshop on sTor age rings and graviTaTional waves physicists work diligently to “tune” t o a x io n s e a r c h e s. R e l a t e d a t t e m p t s a t G W observable t h e m a c h i n e’s p a r a m e t e r s t o a v oi d s u c h d e t e c t i o n u s i n g c a v it i e s w e r e pi o n e e r e d sources of GWs effects. But could accelerator physicists i n t h e 1970 s b y t e a m s i n t h e S o v i e t Un i o n Accelerators meet gravitational waves t u r n t h e t a bl e s a n d s e e k t o e n h a n c e t h e s e and Italy, but RF technology has made effects and observe resonances caused bi g s t r i d e s i n q u a l it y f a c t or s, c o ol i n g a n d Gravitational waves (GWs) crease and al. et Rao gwplotter.com/S by t he passage of GWs? i n s u l a t io n s i n c e t h e n, a n d a n e w s e r ie s o f –12 stretch the fabric of space–time as they 10 37 km ring, 1 nm BPM resolution In accelerators and storage rings, e x p e r i m e nt s a p p e a r s t o b e w e l l j u s t i fie d. ripple out across the universe. As they stochastic 37 km ring, 1 pm BPM resolution c h a r g e d p a r t i c l e s a r e s t e e r e d a n d fo c u s e d Another promising approach for GW background pass through regions where beams in the two directions transverse to detection is atomic-beam interferom- 10–14 circulate in storage rings, they should their motion by dipole, quadrupole and etry. Instead of light interference, as in /K Oide, G Franchetti & F Zimmermann/P Chen & F Zimmermann/P G Franchetti Oide, /K therefore cause charged-particle orbits to higher-order magnets – the “betatron LIGO and VIRGO, an incident GW would seem to contract, as they climb new peaks 10–16 motion” of the beam. The beam is also c a u s e i nt e r fe r e n c e b e t w e e n c a r e f u l l y pr e- and plumb new troughs, with potentially supermassive massive binaries kept bunched in the longitudinal plane pared beams of cold atoms. This approach observable effects. binaries as a result of an energy-dependent path is being pursued by the recently approved resolvable galactic –18 LISA LIGO –13 Proposals in this direction have 10 binaries LHC- length and oscillating electric fields without any backgrounds, as h ~ 10 , AION experiment using ultra-cold- appeared intermittently over the past GWS in radio-frequency (RF) cavities – the a n d l i s t e d t h r e e p o s s i bl e p a t h s t o f u r t h e r strontium atomic clocks over increas- extreme mass type 1A 50 years, including during and after the ratio inspirals “synchrotron motion” of the beam. A improve the sensitivity by several orders ingly large path lengths, including the 10–20 supernovae GW150914 construction of LEP and the LHC. Now unresolvable gravitational wave can resonantly inter- of mag n it ude. R ao a l so h ig h l ig hte d t hat possible use of an LHC access shaft to that the existence of GWs has been estab- characteristic strain galactic binaries ET act with either the transverse betatron storage-ring GW detection potentially house a 100 m device targeting the 0.01 lished by the LIGO and VIRGO detectors, motion of a stored beam, at a frequency allows for an Ear t h-based GW obser v a- to 1 Hz r ange (CERN Courier March/April 10–22 and as new, even larger storage rings of several kHz, or with the longitudinal tory sensitive to millihertz GWs, which 2021 p10). Meanwhile, a space-based LHC, 1 ps noise magnitude compact are being proposed in Europe and China, binary inspirals synchrotron motion at a frequency of could complement space-based laser version, AEDGE, could be realised with this question has renewed relevance. We –24 core collapse tens of her t z. interferometers such as LISA, which is a p a i r o f s a t e l l it e s i n m e d iu m E a r t h or bit 10 supernovae are on the cusp of the era of GW astron- Katsunobu Oide (KEK and CERN) planned to be launched in 2034. This separated by 4.4 × 107 m (CERN Courier pulsars omy – a young and dynamic domain of discussed the transverse betatron res- would improve the sky-localisation of September/October 2019 p23). research with much to discover, in which 10–26 onances that a gravitational wave can the GW source, which is useful for elec- particle accelerators could conceivably 10–10 10–8 10–6 10–4 10–2 100 102 104 106 e x c it e for a b e a m c i r c u l a t i n g i n a s t or a g e tromagnetic follow-up studies with Storage rings as sources play a major role. frequency [Hz] r i n g. T y pic a l b e t a t r o n f r e q u e n c ie s for t h e astronomical telescopes. E x t r a ord i n a r i l y, s t or a g e r i n g s c o u l d a c t From 2 February to 31 March this LHC are a few kHz, potentially offering not only as GW detectors, but also as year, a topical virtual workshop titled Sources and sensitivities Gravitational-wave sources (shaded) and detector sensitivities (lines), sensitivity to GWs with frequencies of a Out of the ordinary observable sources of GWs. Pisin Chen “Storage Rings and Gravitational Waves” including those for the space-based interferometer LISA and the ground-based interferometers LIGO and s i m i l a r or d e r o f m a g n it u d e. St a r t i n g f r o m More exotic accelerators were also (NT U Ta iw a n) d isc ussed how relat iv is- (SRGW2021) shone light on this tanta- the Einstein Telescope. Accelerator-based detection methods and sources are superimposed based on a s t a n d a rd 30 k m r i n g, O id e-s a n pr o p o s e d mooted. A “coasting-beam” experiment tic charged particles executing circu- lising possibility. Organised within the optimistic assumptions that require future confirmation. special beam-optical insertions with a might have zero restoring voltage and no lar orbital motion can emit GWs in two European Union’s Horizon 2020 ARIES large beta function, which would serve synchrotron oscillations. Cold “crystal- channels: “gravitational synchrotron project, the meeting brought together presented a vivid account of the history and earthquakes on the other side of the a s “G W a nt e n n a s” t o e n h a n c e t h e r e s o - line” beams of stable ordered 1D, 2D or 3D r a d i a t io n” (G SR) e m it t e d d i r e c t l y b y t h e more than 100 accelerator experts, of GWs, revealing how subtle they are planet. Famously, LEP’s beam-energy n a n c e s t r e n g t h, r e s u lt i n g i n 37.5 km-long structures of ions (CERN Courier No ve m- massive particle, and “resonant conver- particle physicists and members of the theoretically. It took about 40 years resolution was so precise that it detected optics. Among several parameters, the ber 2001 p8) could open up a whole new sion” in which, via the Gertsenshtein gravitational-physics community to and a number of conflicting papers to a diurnal distortion of the 27 km ring at sensitivity to GWs should depend on the f r e q u e n c y s p e c t r u m, a s t h e p h o n o n s p e c- effect, electromagnetic synchrotron explore several intriguing proposals. definitively establish their existence. an amplitude of a single millimetre, and size of the ring. trum that could be excited by a GW could radiation (EMSR) is converted into GWs. Bangalore S Sathyaprakash (Penn State the LHC beam-position-monitor system Suvrat Rao (Hamburg University) pre- e a s i l y e x t e n d u p t o t h e M H z r a n g e. W it e k John Jowett (GSI, retired from CERN) Theoretically subtle a n d C a rd i ff) r e v i e w e d t h e m a i n e x p e cted can achieve measurement resolutions on sented an analysis of the longitudinal K r a s n y (L PN H E) s u g g e s t e d s t or i n g b e a m s a n d F r it z C a s p e r s (a l s o r e t i r e d f r o m C E R N) GWs are extremely feebly interacting. sources of GWs: the gravitational col- the average circumference approaching b e a m r e s p o n s e o f t h e L HC. A n i m pi n g i n g c o n s i s t i n g o f “a t o m i c c l o c k s” i n t h e L HC: recalled that GSR from beams at the SPS The cooling and expanding universe lapse of binaries of compact objects the micrometre scale over time inter- GW affects the revolution period, in a decay times and transition rates could be a n d o t h e r c ol l id e r s h a d b e e n d i s c u s s e d a t should have become “transparent” to such as black holes, neutron stars and vals of one hour. While impressive, given similar way to the static gravitational modified by an incident GW. The stored CERN as early as the 1980s. It was real- them early in its history, long before white dwarfs; supernovae and other that these machines are designed with gradient effect due to the presence of particles could, for example, include the ised that these beams would be among the timescales probed through other transient phenomena; spinning neu- completely different goals in mind, it Mont Blanc (which alters the revolution excited partially stripped heavy ions that t he m o s t p o we r f u l t e r re s t r i a l s o u rc e s o f known phenomena. Detecting cos- tron stars; and stochastic backgrounds is still far from the precision achieved time at the level of 10–16 s) and the diur- a r e t h e b a s i s o f a “g a m m a f a c t or y” (CERN gravitational radiation, although the total mological backgrounds of GWs would, with either astrophysical or cosmolog- by LIGO and VIRGO. However, one can nal effect of the changing locations of Courier November 2017 p7). radiated power would still be many orders therefore, provide us with a picture of ical origins. The GW frequency range of strongly enhance the sensitivity to GWs the Sun and Moon (10–18 s) – the latter Finally on the storage-ring front, of magnitude lower than from regular the universe at earlier times that we can interest extends from 0.1 nHz to 1 MHz by exploiting resonant effects and the effect being about six orders of magni- Andrey Ivanov (TU Vienna) and co- synchrotron radiation. The dominant currently access, prior to photon decou- (see “Sources and sensitivities” figure). long distances travelled by the particles tude smaller than the tidal effect on the workers discussed t he possibly shr in k- frequency of direct GSR is the revolu- pling and Big-Bang nucleosynthesis. It Raffaele Flaminio (LAPP Annecy) over their storage times. In one hour, ring circumference. ing circumference of a storage ring, such tion frequency, ~10 kHz, while the dom- could also shed light on high-energy reviewed the mindboggling precision We are on protons at the LHC travel through the The longitudinal beam response to a as the 1.4 km light source SPring-8 in inant frequency of resonant EMSR–GSR 3 phenomena, such as high-temperature of VIRGO and LIGO, which can meas- the cusp of ring about 40 million times. In prin- GW should be enhanced for perturba- Japan, under the influence of the relic conversion is a factor γ higher, around phase transitions, inflation and new ure motion 10,000 times smaller than the era of ciple, the precision of modern accel- t i o n s c l o s e t o t h e s y n c h r o t r o n f r e q u e n c y, GW background. 10 THz at t he LHC, conceiv ably a l low i ng heavy particles that cannot be directly the width of an atomic nucleus. Jörg erator optics could allow storage rings w h i c h, for t h e L HC, w o u l d b e i n t h e r a n g e Delegates at SRGW2021 also proposed the observation of gravitons. If all par- produced in the laboratory. Wenninger (CERN) reported the simi- gravitational- and accelerator technologies to cover a 10 t o 60 Hz. Raffaele D’Agnolo (IPhT) esti- completely different ways of using t i c l e s a n d b u n c h e s o f a b e a m e x c it e d t h e In the opening session of the work- larly impressive sensitivity of LEP and wave portion of the enormous GW frequency mated the sensitivity to the gravitational accelerator technology to detect GWs. GW coherently, the space–time metric s s shop, Jorge Cervantes (ININ Mexico) the LHC to small effects, such as tides astronomy range of interest. strain, h, at the synchrotron frequency, S e b a s t i a n E l l i s (I P hT) e x pl a i n e d h o w a n perturbation has been estimated to

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FIELD NOTES FIELD NOTES

–18 be as large as hGSR ~ 10 . Gravitons could proposals considered closest to imple- Gravitons could sions in this emerging field attest to the detector is an interesting example where den) groups illustrated measurements We now impact and the uncertain availability and also be emitted via “gravitational beam- mentations: resonant betatron oscillations be emitted via promise of employing accelerators in a HFO could replace CF4. In this case, its of transport parameters, opening pos- need to create price of freon-based gases, preparing a strahlung” during the collision with an near 10 kHz; changes in the revolution gravitational c o m pl e t e l y d i ffe r e nt w a y t o e it h e r d e t ect decomposition could even be a positive sibilities of collaboration, while the Bari a compendium mitigation plan for future experiments opposing beam, perhaps producing the period using “low-energy” coasting ion- or generate GWs. The subtleties of the factor, however more studies are needed. group sought feedback and collaboration is of fundamental importance to the of simulations most prominent GW signal at future pro- beams without a longitudinally focusing beamstrahlung particle dynamics when embedded in We now need to create a compendium on a proposal to precisely measure trans- high-energy-physics community, and posed lepton colliders. At the LHC, argued RF system; “heterodyne” detection using an oscillating fabric of space and time, of simulations and measurements for port parameters for green gases in MPGDs and the next generation of detectors must Caspers, such signals could be detected by SRF cavities up to 10 MHz; beam-generated and the inherent sensitivity problems in “green” gases in a similar way to the using electron and laser beams. measurements be completely designed around eco- a torsion-balance experiment with a very GWs at the LHC; and atomic interferome- detecting GWs, pose exceptional chal- concerted effort in the 1990s and 2000s F ut u r e c h a l l e n g e s w i l l b e s i g n i fic a nt. for “green” mixtures. Although obtaining funding sensitive, resonant mechanical pickup try. These potential components of a future lenges. The great interest prompted by that proved indispensable to the design The volumes of detector systems for the gases for this work can be difficult, for example installed close to the beam in one of the R& D pl a n c o v e r s i g n i fic a nt r e g io n s o f t he SRGW2021, and the tantalising prelim- of the LHC detectors. To this end, the High-Luminosity LHC and the proposed due to a lack of expected technological arcs. In a phase-lock mode of opera- enormous GW frequency space. inary findings from this workshop, call INRS-hosted LXCAT database enables Future Circular Collider, for example, breakthroughs in low-energy plasma tion, an effective resolution bandwidth for more thorough investigations into the sharing and evaluation of data to range from 10 to 100 m3, posing a sig- physics, the workshop showed that a of millihertz or below could be possible, New horizons harnessing future storage rings and model non-equilibrium low-temperature n i fic a nt e n v i r o n m e nt a l t h r e a t i n t h e case vibrant cadre of physicists is commit- opening the exciting prospect of detect- Apart from an informal meeting at accelerator technologies for GW physics. plasmas. Users can upload data on elec- of leaks. Furthermore, since 2014 an EU ted to taking the field forward. The next ing synthetic sources of GWs. CERN in the 1990s, SRGW2021 was the tron- and ion-scattering cross sections “F-gas” regulation has come into force, workshop w ill ta ke place in 2022. The concluding workshop discussion, first workshop to link accelerators and Raffaele Tito D’Agnolo IPhT, and compare “swarm” parameters. The with the aim of reducing sales to one- moderated by John Ellis (King’s College GWs, and bring together the implicated Giuliano Franchetti GSI and ETH Zürich, Aachen and HZDR (Dres- fifth by 2030. Given the environmental Archana Sharma CERN. London), focused on the GW-detection scientific communities. Lively discus- Frank Zimmermann CERN. EuropEan Consortium for astropartiClE thEory annual symposium Mini-workshop on gas tr ansport par a Meters Greening B Regnery Astroparticle theory in rude health

gaseous detectors The European Consortium for Astropar- Rayner Nenad/M N Sarcevic/R physics and cosmology. Alessandra Buo- ticle theory (EuCAPT) held its first annual nanno (Max Planck Institute for Gravi- Thanks to their large volumes and cost symposium from 5 to 7 May. Hundreds of tational Physics) illustrated the exciting effectiveness, particle-physics experi- theoretical physicists from Europe and prospects for this new field of research, ments rely heavily on gaseous detectors. beyond met online to discuss the pres- whose potential for discovering new Unfortunately, environmentally harm- ent and future of astroparticle physics physics is attracting enormous interest f u l h yd r o flu or o c a r b o n s k n o w n a s f r e o ns and cosmology, in a dense and exciting from particle and astroparticle theorists. play an important role in traditional gas meeting that featured 29 invited pres- The connection between cosmic rays, mixtures. To address this issue, more entations, 42 lightning talks by young gamma rays and high-energy neutrinos than 200 gas-detector experts partic- researchers, and two community-wide w a s e x pl or e d i n t h e fi n a l o ut l o o k b y E l e na ipated in a workshop hosted online by brainstorming sessions. Amato (Arcetri Astrophysical Observa- CERN on 22 April to study the operational Participants discussed a wide array of tory), who highlighted how progress in behaviour of novel gases and alternative topics at the interface between particle theory and observations is leading the gas mixtures. physics, astrophysics and cosmology, community to reconsider some long-held Freon-based gases are essential to with particular emphasis on the chal- beliefs – such as the idea that supernova many detectors currently used at CERN, l e n g e s a n d o p p or t u n it i e s for t h e s e fie l d s remnants are the acceleration sites of especially for tracking and triggering. in the next decade. Rather than focus- cosmic rays up to the so-called “knee” Examples run from muon systems, ing on experimental activities and the Unleashing potential A visualisation of the “EuCAPT census” – and stimulating new ideas. ring-imaging Cherenkov (RICH) detec- discoveries they might enable, the ses- of theoretical astroparticle physicists and cosmologists who are In line with EuCAPT’s mission, the tors and time-projection chambers sions were structured around thematic affiliated to a research institution in a European country. local organisers and the consortium’s

(TPCs) to wire chambers, resistive-plate Trigger and track for example, the recuperation of CF4 by Unfortunately, these conditions are also areas and explored the interdisciplinary steering committee organised a series chambers (RPCs) and micro-pattern gas In ATLAS and CMS the CMS experiment’s cathode- present in gaseous detectors, potentially multi-messenger aspects of each. model of cosmology, and allow us to gain of community-building activities. detectors (MPGDs). While the primary gas (pictured), gaseous strip-chamber (CSC) muon detector and leading to detector aging. In addition to Two sessions were dedicated to cos- insights into the physics of dark matter, Participants stressed the importance in the mixture is typically a noble gas, detectors form the the LHCb experiment’s RICH-2 detec- their stability, there is also the challenge mology, exploring the early and late uni- dark energy and gravity. of supporting diversity and inclusivity, adding a “quencher” gas helps achieve backbone of the tor. A complex gas-recuperation system of adapting current LHC detectors, given verse. As stressed by Geraldine Servant New strategies to go beyond the stand- a continuing high priority for EuCAPT,

a stable gas gain, well separated from experiments’ for the C2H2F4 (R134a) in RPC detectors that access is difficult and many com- (Hamburg), several unresolved puzzles ard models of particle physics and cosmol- while a second brainstorming session the noise of the electronics. Large gas muon systems. is also under study, and physicists are ponents cannot be replaced. of particle physics – such as the origin ogy were also discussed by Marco Cirelli was devoted to the discussion of the molecules such as freons absorb energy exploring the use of commonplace gases. Roberto Guida (CERN), Davide Piccolo of dark matter, the baryon asymmetry, (LPTHE) and Manfred Lindner (Heidel- EuCAPT white paper currently being in relevant vibrational and rotational In the future, new silicon photomulti- (F r a s c a t i), R o b Ve e n h o f (Ulu d a ğ Un i v e r- a n d i n fl a t io n – a r e d i r e c t l y l i n k e d t othe berg), in the framework of dark-matter written, which should be published by modes of excitation, thereby prevent- pliers could reduce chromatic error and sity) and Piet Verwilligen (Bari) convened early universe, and new observational searches and neutrino physics, respec- September. Last but not least, Hannah ing secondary effects such as photon increase photon yield, potentially allow- workshop sessions at the April event. probes may soon shed new light on them. tively. Progress in both fields is currently Banks (Cambridge), Francesca Capel (TU

feedback and field emission. Extensive ing CF4 to be replaced with CO2. Mean- Groups from Turin, Frascati, Rome, Julien Lesgourgues (Aachen) showed not limited by a lack of ideas – we are Munich) and Charles Dalang (Univer-

R&D is needed to reach the stringent per- while, in LHCb’s RICH-1 detector, C4F10 CERN and GSI presented results based how the very same puzzles are also linked actually witnessing a proliferation of sity of Geneva) received prizes for the formance required of each gas mixture. could possibly be replaced with hydro- on the new hydro-fluoro-olefin (HFO) to the late universe, and cautiously elabo- theoretically well-motivated models – but best lightning talks, and Niko Sarcevic

CERN has developed several strate- carbons like C4H10 i f t h e fl a m m a bi l it y r i s k mixture with the addition of neutral rated on a series of possible inconsisten- by the difficulty of identifying experi- (Newcastle) was awarded an “outstand-

gies to reduce greenhouse-gas emissions is addressed. gases such as helium and CO2 as a way of cies between physical quantities inferred mental strategies to conclusively validate ing contributor” prize for the help and from particle detectors. As demonstrated Finally, alternative “eco-gases” are lowering the high working-point voltage. from early- and late-universe probes, or rule them out. Much of the discussion support she provides for the analysis of by the ALICE experiment’s TPC, gas- the subject of intense R&D. Eco-gases Despite challenges related to the larger for example the Hubble constant. Those here concerned prospects for detecting the EuCAPT census (pictured). recirculation systems can reduce emis- have a low global-warming potential signal charge and streamer probability, inconsistencies represent both a chal- new physics with dedicated experiments. The next symposium will take place sions by almost 100%. When it is not because of their very limited stability encouraging results have been obtained lenge and an extraordinary opportunity and multi-messenger observations. in 2022, hopefully in person, at CERN. possible to recirculate all of the gas in the atmosphere as they react with in test beams in the presence of LHC-like for cosmology, as they might “break” Gravitational waves have added a new s mixture, gas recuperation is an option – water or decompose in ultraviolet light. background gamma rays. CMS’s CSC the standard Lambda–cold-dark-matter observational probe in astroparticle Gianfranco Bertone EuCAPT director.

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Making our world more productive FEATURE MEDICAL TECHNOLOGY CERN’S IMPACT ON Partner you can count on – MEDICAL TECHNOLOGY

no matter how cold it gets D Dominguez/KTTGROUP-PHO-TECH-2018-002-4 Frontier instruments like the Linde Kryotechnik LHC and its detectors not only push back the boundaries of our

For over eight decades, we have been enabling ground-breaking discoveries knowledge, but also catalyse that challenge the boundaries of physics. As the world’s leading cryogenic innovative technology for medical engineering company, we have the technologies, experience and skills to applications, writes Manuela Cirilli. keep cool – while the scientists unravel the secrets of science.

Linde Kryotechnik – your trusted partner. oday, the tools of experimental particle phys- ics are ubiquitous in hospitals and biomedical No matter where the journey takes you. T research. Particle beams damage cancer cells; high-performance computing infrastructures acceler- ate drug discoveries; computer simulations of how par- ticles interact with matter are used to model the effects of radiation on biological tissues; and a diverse range of particle-physics-inspired detectors, from wire chambers to scintillating crystals to pixel detectors, all find new vocations imaging the human body. CERN has actively pursued medical applications of its technologies as far back as the 1970s. At that time, knowledge transfer happened – mostly serendipitously – through the initiative of individual researchers. An emi- nent example is Georges Charpak, a detector physicist of GaToroid Innovative gantry designs reduce the size, weight and complexity outstanding creativity who invented the Nobel-prize- of the massive magnetic structures that allow a hadron-therapy beam (red) to winning multiwire proportional chamber (MWPC) at CERN reach the patient from different angles. in 1968.The MWPC’s ability to record millions of particle tracks per second opened a new era for particle physics (the uptake of glucose, for example, could be used to iden- (CERN Courier December 1992 p1). But Charpak strived to tify a malignant tumour). Pairs of back-to-back 511 keV ensure that the technology could also be used outside photons are detected when a positron annihilates with an Sync up with our experts at the the field – for example in medical imaging, where its electron in the surrounding matter, allowing the tumour sensitivity promised to reduce radiation doses during to be triangulated. imaging procedures – and in 1989 he founded a company Pioneering developments in PET instrumentation took CEC/ICMC 2021 that developed an imaging technology for radiography place in the 1970s. While most scanners were based on which is currently deployed as an orthopaedic application. scintillating crystals, the work done with wire cham- Virtual Conference, July 19–23 Following his example, CERN has continued to build a bers at the University of California at Berkeley inspired culture of entrepreneurship ever since. CERN physicists David Townsend and Alan Jeavons to use high-density avalanche chambers (HIDACs) – Charpak’s Triangulating tumours detector plus a photon-conversion layer (CERN Courier Linde Kryotechnik AG Since as far back as the 1950s, a stand-out applica- June 2005 p23). In 1977, with the participation of CERN Daettlikonerstrasse 5, 8422 Pfungen, Switzerland tion for particle-physics detector technology has been radiobiologist Marilena Streit-Bianchi, this technology positron-emission tomography (PET) – a “functional” was used to create some of the first PET images, most Phone +41 52 304-0555, www.linde-kryotechnik.ch technique that images changes in the metabolic process famously of a mouse. The HIDAC detector later contrib- rather than anatomy. The patient is injected with a com- uted significantly to 3D PET image reconstruction, while a THE AUTHOR Linde Cryogenics pound carrying a positron-emitting isotope, which accu- prototype partial-ring tomograph developed at CERN was Manuela Cirilli Division of Linde Process Plants, Inc. mulates in areas of the body with high metabolic activity a forerunner for combined PET and computed tomography CERN. 6100 South Yale Avenue, Suite 1200, Tulsa, Oklahoma 74136, USA Phone +1 918 477-1200, Fax +1 918 477-1100, www.leamericas.com CERN COURIER JULY/AUGUST 2021 23

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rieCRNPOTO-201803-081-2 T N-PHO ice/CER Br M tiling the chips on all four sides. Knowledge transfer at CERN Medipix and Timepix chips find applications in widely CERN varied fields, from medical imaging to cultural heritage, As a publicly funded laboratory, CERN M a rs Bioi mag i ng space dosimetry, materials analysis and education. The has a remit, in addition to its core industrial partners and licence holders commercialising the mission to perform fundamental technology range from established enterprises to start-up research in particle physics, to expand companies. In the medical field, the technology has been the opportunities for its technology and applied to X-ray CT prototype systems for digital mam- expertise to deliver tangible benefits m o g r a p h y, C T i m a g e r s for m a m m o g r a p h y, a n d b e t a- a n d to society. The CERN Knowledge gamma-autoradiography o f biolo g ic a l s a m ple s. I n 2018 t h e Transfer group strives to maximise first 3D colourX-ray images of human extremities were the impact of CERN technologies and taken by a scanner developed by MARS Bioimaging Ltd, know-how on society in many ways, using the Medipix3 technology. By analysing the spectrum including through the establishment Colour X-ray Spectroscopic techniques using CERN’s Medipix chips may be used to Radioisotopes In the MEDICIS project, non-conventional r e c ord e d i n e a c h pi x e l, t h e s c a n n e r c a n d i s t i n g u i s h mu lt i ple of partnerships with clinical, industrial partly cut away water (blue), to reveal bone and organs in this colour X-ray of a mouse. isotopes are collected by mass separation. m at e r i a l s i n a s i n g le s c a n, o p e n i n g up a n e w d i m e n s io n i n and academic actors, support to medical X-ray i m a g i n g: w it h t h i s c h i p, i m a g e s a r e n o lo n g e r budding entrepreneurs and seed Tangible benefitsGEMPix detectors For example, the avalanche photodiodes developed for black and white, but in colour (see “Colour X-ray” image). funding to CERN personnel. are being evaluated for use in quality the CMS electromagnetic calorimeter were adapted for Although the primary aim of the Timepix3 chip was Supporting the knowledge-transfer assurance in hadron therapy. the ClearPEM breast-imaging prototype, and technology applications outside of particle physics, its development process from particle physics to developed for detecting pancreatic and prostate cancer a l s o le d d i r e c t l y t o n e w s olut io n s i n high-energy p h y s ic s, medical research and the med-tech through a dedicated strategy document

Ja n Ja k ůbek (IE A P, Pr ag ue) (E ndoT OFPET-US) inspired the “barrel timing layer” of such as the VELOpix chip for the ongoing LHCb upgrade, industry is a promising avenue to boost approved by its Council in June 2017 crystals that will instrument the central portion of the which permits data-driven trigger-free operation for healthcare innovation and provide (CERN Courier January/February 2018 (a) (b) (c) (d) CMS detector during LHC Run 3. the first time in a pixel vertex detector in a high-rate solutions to present and future health p5) . CERN will continue its efforts to Hadron therapy In these images, Timepix chips were combined with a silicon experiment. challenges. CERN has provided a maximise the impact of the laboratory’s detector to visualise energy deposition from (a) 48 MeV protons, (b) 221 MeV Pixel perfect framework for the application of its know-how and technologies on the protons, (c) 89 MeV/u carbon ions and (d) 430 MeV/u carbon ions. In each case, In the same 30-year period, the family of Medipix and Dosimetry technologies to the medical domain medical sector. secondary particles are present only at the higher energy. Timepix read-out c h i p s h a s a r g u a bl y m a d e a n e v e n bi g g e r C E R N t e a m s a r e a l s o e x plor i n g t h e p o t e nt i a l u s e s o f M e d i pi x impact on med-tech a n d o t h e r a p pl ic at io n fie ld s, b e c o m i n g tec hnolog y in dosimet r y. In 2019, for example, Timepix3 (CT) scanners. Townsend went on to work at the Cantonal one of CERN’s most successful technology-transfer cases. was employed to determine the exposure of medical per- t h e m a g n e t ic fie ld o n, it h a s fo u n d a p pl ic at io n s i n s e v eral Hospital in Geneva and then in the US, where his group Developed with the support of four successive Medipix s o n n e l t o io n i s i n g r a d i at io n i n a n i nt e r v e nt io n a l r a d iolo g y other tasks, such as radiation measurements on perma- helped develop the first PET/CT scanner, which combines c ol l a b or at io n s, i n v ol v i n g a t o t a l o f 37 r e s e a rc h i n s t it ut e s, t h e at r e at C h r i s t c hu rc h Ho s pit a l i n Ne w Z e a l a n d. T h e c h i p nent magnets, radiation surveys at PET-M R I scanners and functional and anatomic imaging. the technology is inspired by the high-resolution hybrid was able to map the radiation fluence and energy spectrum at MRI-guided radiation therapy linacs. Meanwhile, the pixel detectors initially developed to address the chal- of the scattered photon field that reaches the practitioners, radon dose monitor (RaDoM) tackles exposure to radon, Crystal clear lenges of particle tracking in the innermost layers of the a n d c a n a l s o pr o v id e i n for m at io n a b o ut w h ic h p a r t s o f t h e a natural radioactive gas that is the second leading cause In the onion-like configuration of a collider detector, an LHC experiments. In hybrid detectors, the sensor array body are most e x posed to radiat ion. of lung c a ncer a f ter smok i ng. The R a DoM de v ice d i re c t ly electromagnetic calorimeter often surrounds a descendant and the read-out chip are manufactured independently Meanwhile, “GEMPix” detectors are being evaluated estimates the dose by reproducing the energy deposition of Charpak’s wire chambers, causing photons and electrons and later coupled by a bump-bonding pr o c e s s. T h i s m e a n s for use in quality assurance in hadron therapy. GEMPix inside the lung instead of deriving the dose from a meas- to cascade and measuring their energy. In 1991, to tackle that a variety of sensors can be connected to the Medipix couples gas electron multipliers (GEMs) – a type of gas- urement of radon concentration in air; CERN also developed the challenges posed by future detectors at the LHC, the a n d T i m e pi x c h i p s, a c c ord i n g t o t h e n e e d s o f t h e e n d u s e r. eous ionisation detector developed at CERN – with the a cloud-based service to collect and analyse the data, to C r y s t a l C le a r c ol l a b or at io n w a s for m e d t o s t ud y i n n o v at i v e The first Medipix chip produced in the 1990s by the Medipix integrated circuit as readout to provide a hybrid control the measurements and to drive mitigation meas- scintillating crystals suitable for electromagnetic calo- Medipix1 collaboration was based on the front-end archi- device capable of detecting all types of radiation with a ures based on real time data. The technology is licensed r i met r y (CERN Courier Novemb er 2016 p17). Si nce it s ea rly t e c t u r e o f t h e O m e g a3 c h i p u s e d b y t h e half-million-pixel h i g h s p at i a l r e s olut io n. Fol lo w i n g i n it i a l r e s u lt s f r o m t e s t s to the CERN spin-off BAQ. y e a r s, C r y s t a l C le a r a l s o s o u g ht t o a p pl y t h e t e c h n olo g y t o t r a c k e r o f t h e WA97 e x p e r i m e nt, w h ic h s t ud ie d s t r a n g e n e s s on a carbon-ion beam performed at the National Centre other fields, including healthcare. Several breast, pancreas, production in lead–ion collisions. The upgraded Medipix1 for Oncological Hadrontherapy (CNAO) in Pavia, Italy, a Cancer treatments prostate and animal-dedicated PET scanner prototypes c h i p a l s o i n c lud e d a c o u nt e r p e r pi x e l. T h i s d e m o n s t r at e d large-area GEMPix detector with an innovative optical Ha v i n g s u r v e y e d t h e m e d ic a l a p pl ic at io n s o f p a r t ic le d e t e c- have since been developed, and the collaboration contin- that the chips could work like a digital camera, providing read-out i s n o w b e i n g d e v e lo p e d at C E R N i n c ol l a b or at io n tors, we t ur n to t he tec h nolog y d r iv i ng t he bea ms t hem- ues to push the limits of coincidence-time resolution for high-resolution, high-contrast and noise-hit-free images, with the Holst Centre in the Netherlands. A version of the selves. Radiotherapy is a mainstay of cancer treatment, time-of-flight (TOF) PET. m a k i n g t h e m u n iq ue l y s u it a ble for m e d ic a l a p pl ic at io n s. GE M P i x c a l le d GE MT EQ i s a l s o c u r re nt ly u nde r de ve lop- using ionising radiation to damage the DNA of cancer cells. In TOF–PET, the difference between the arrival times of Medipix2 improved spatial resolution and produced a mod- ment at CERN for use in “microdosimetry”, which studies In most cases, a particle accelerator is used to generate a the two back-to-back photons is recorded, allowing the i fie d v e r s io n c a l le d T i m e pi x t h at offe r s t i m e or a m pl itude the temporal and spatial distributions of absorbed energy therapeutic beam. Conventional radiation therapy uses location of the annihilation along the axis connecting the measurements in addition to hit counting. Medipix3 and i n biolo g ic a l m at t e r t o i m pr o v e t h e s a fe t y a n d e ffe c t i v e n e s s X-rays generated by a linac, and is widely available at d e t e c t io n p oi nt s t o b e pi n n e d d o w n. B e t t e r t i m e r e s olut io n Timepix3 then allowed the energy of each individual of cancer treatments. relatively low cost. Medipix and therefore improves image quality and reduces the acqui- photon to be measured – Medipix3 allocates incoming Two further dosimetry applications illustrate how tech- Radiotherapy with protons was first proposed by Fer- Timepix read- s it io n t i m e a n d r a d i at io n d o s e t o t h e p at ie nt. C r y s t a l C le a r hits to energy bins in each pixel, providing colour X-ray nologies developed for CERN’s needs have expanded into milab’s founding director Robert Wilson in 1946 while continues this work to this day through the development images, while Timepix3 times hits with a precision of commercial medical applications. The B-RAD, a hand-held he was at Berkeley, and interest in the use of heavier ions out chips have of innovative scintillating-detector concepts, including 1.6 n s, a n d s e n d s t h e f u l l h it d at a – c o ord i n at e, a m pl it ud e radiation survey meter designed to operate in strong mag- such as carbon arose soon after. While X-rays lo s e e n e r g y become one of at a state-of-the-art laborator y at CERN. and time – off chip. Most recently, the Medipix4 collab- n e t ic fie ld s, w a s d e v e lo p e d b y C E R N i n c ol l a b or at io nwith roughly exponentially as they penetrate tissue, protons CERN’s most The dual aims of the collaboration have led to oration, which was launched in 2016, is designing chips the Polytechnic of Milan and is now available off-the-shelf a n d o t h e r io n s d e p o s it a l m o s t a l l o f t h e i r e n e r g y i n a s h a r p successful cross-fertilisation, whereby the work done for high-energy that can seamlessly cover large areas, and is developing from an Italian company. Originally conceived for radiation “Bragg” peak at the very end of their path, enabling the technology- physics spills over to medical imaging, and vice versa. new read-out architectures, thanks to the possibility of surveys around the LHC experiments and inside ATLAS with dose to be delivered on the tumour target, while sparing transfer cases

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FEATURE MEDICAL TECHNOLOGY FEATURE MEDICAL TECHNOLOGY

ion-therapy facilities. The goal is to propel the use of ion iaging and treatent. In operation since late 2, discoveries and siulate how the SARS-CoV-2 virus spreads therapy, given that proton installations are already com- MDICIS will expand the range of radioisotopes availale through the population, aong other applications, and erciall availale and that onl four ion centres exist in for edical research soe of which can e produced onl is now eing extended eond iological siulations to Europe, all based on bespoke solutions. at C and send the to partner hospitals and research visualise the collective ehaviour of groups in societ.

de MontignioDnaMo N I M M S i s or g a n i s e d a lo n g fo u r d i ff e r e nt l i n e s o f a c t i v- centres for further studies. During its 2 and 22 har- Man ore proects related to edical applications are ities. The fi rst aims to reduce the footprint of facilities by vesting capaigns, for exaple, MDICIS deonstrated in their initial phases. The readth of knowledge and skills developing new superconducting agnet designs with large the capailit of purifing isotopes such as r or S to availale at C was also evident during the COVID-19 apertures and curvatures, and for pulsed operation. The new purit grades, aking the suitale for innovative pandemic when the laboratory contributed to the eff orts s e c on d i s t h e d e s i g n o f a c omp a c t l i n e a r a c c e le r at or o p t i- treatents such as targeted radioiunotherap. of the particle-phsics community in fi elds ranging from mised for installation in hospitals, which includes an RFQ innovative ventilators to asks and shields, fro data based on the design of the proton therapy RFQ, and a novel Data handlin and siulations anageent tools to open-data repositories, and fro a source for fully-stripped caron ions. The third concerns The expertise of particle phsicists in data handling and platfor to odel the concentration of viruses in enclosed two innovative gantr designs, with the ai of reducing simulation tools are also increasingly fi nding applications spaces to epideiologic studies and proxiit-sensing the size, weight and complexity of the massive magnetic i n t h e bio m e d ic a l fi e ld. T h e F LU K A a n d G e a nt 4 s i mu l at io n devices, such as those developed Teraee. structures that allow the ea to reach the patient fro toolkits, for exaple, are eing used in several applica- Fundamental research has a priceless goal: knowledge The expertise diff erent angles: the SIGRUM lightweight rotational gantry tions, fro detector odelling to treatent planning. for the sake of knowledge. The theories of relativit and of particle originally proposed by TERA, and the GaToroid gantry ecentl, C contriuted its know-how in large-scale uantu echanics were considered astract and esoteric physicists in Coputational the surrounding health tissues. Caron ions have the i nvented at CER N wh ic h el i m i nates t he ne ed to mec ha n- coputing to the ioDnaMo collaoration, initiated when the were developed a centur later, we owe to the data handlin neuroscience additional advantage of a higher radiobiological eff ec- icall rotate the structure using a toroidal agnet (see C E R N o p e n l a b t o g e t h e r w it h Ne wc a s t le Un i v e r s it y, w h ic h t h e r e m a r k a ble pr e c i s io n o f GP S s y s t e m s a n d t h e t r a n s i s- ioDynaMo tiveness, and can control tuours that are radio-resistant fi g u r e “G a Tor oid”). F i n a l l y, n e w high-current snchrotron initiall aied to provide a standardised, high-perforance tors that are the foundation of the electronics-ased world and siulation simulation of a to X-rays and protons. idespread adoption of hadron designs will e developed to reduce the cost and footprint and open-source platfor to support coplex iological we live in. Particle-physics research acts as a traillaer tools are dendritic arbour. therap is, however, liited the cost and coplexit of facilities while reducing the treatent tie copared to simulations (see fi gure “Computational neuroscience”). for disruptive technologies in the fi elds of accelerators, increasinly of the reuired infrastructures, and the need for ore present uropean ion-therapy c e nt r e s: t h e s e w i l l i n c lud e hiding its coputational coplexit, ioDnaMo detectors and coputing. ven though their ipact is often fi nding pre-clinical and clinical studies. a superconducting and a room-temperature option, and allows researchers to easil create, run and visualise D diffi cult to track as it is indirect and diff used over time, applications in advanced features such as multi-turn injection for 10 agent-ased siulations. It is alread used acadeia these technologies have alread greatl contriuted to the the ioedical PIMM and NIMM particles per pulse, fast and slow extraction, and ultiple and industr to siulate cancer growth, accelerate drug advances of odern edicine and will continue to do so.  fi e l d etween and 2, under the ipulsion of Ugo ion operation. Through NIMMS, CERN is contributing to aldi, Meinhard iegler and hil rant, C hosted the eff orts of a fl ourishing European community, and a the Proton-Ion Medical Machine Study (PIMMS). PIMMS nuer of collaorations have een alread estalished. produced and ade pulicl availale an optiised design nother recent exaple of frontier radiotherap techniues for a cancer-therapy snchrotron capale of using oth is the collaboration with Switzerland’s Lausanne University protons and caron ions. fter further enhanceent Hospital (CHUV) to build a new cancer therapy facility that aldis T foundation, and with seinal contriutions would deliver high doses of radiation fro very-high-energy from Italian research organisation INFN, the PIMMS concept electrons (VHEE) in milliseconds instead of minutes. The Fast Pulse Generators & evolved into the accelerator at the heart of the C hadron goal here is to exploit the so-called FLASH eff ect, wherein therap centre in avia. The Medustron centre in iener radiation doses adinistered over short tie periods appear eustadt, ustria, was then ased on the C design. C to daage tuours ore than health tissue, potentiall Arbitrary Waveform Generators continues to collaorate with C and Medustron iniising harful s i d e - e ff e c t s . This pioneering installation sharing its expertise in accelerator and agnet technologies will e ased on the high-gradient accelerator technolog (CERN Courier Januar y/Febr uar y 2018 p25). developed for the proposed CLIC electron–positron collider. In the 2010s, CERN teams put to use the experience gained Va r io u s r e s e a rc h t e a m s h a v e b e e n p e r for m i n g t h e i r bio m e d- in the construction of inac 4, which ecae the source ic a l r e s e a rc h r e l at e d t o V H E E a n d F L A SH at t h e C E R N L i n e a r of proton eas for the HC in 22, and developed an Electron Accelerator for Research (CLEAR), one of the few extreel copact high-frequency radio-frequency quad- facilit ies av ailable for c haracterising V HEE beams. rupole (RFQ) to be used as injector for a new generation of high-frequency, copact linear accelerators for proton Radioisotopes therapy. The RFQ accelerates the proton beam to 5 MeV CERN’s accelerator technology is also deployed in a com- after only 2 m, and operates at 750 MHz – almost double pletely diff erent way to produce innovative radioisotopes the frequency of conventional RFQs. A major advantage of for medical research. In nuclear medicine, radioisotopes using linacs for proton therap is the possiilit of changing are used oth for internal radiotherap and for diagnosis the energ of the ea, and hence the depth of treatent of cancer and other diseases, and progress has alwas in the body, from pulse to pulse by switching off some of been connected to the availability of novel radioiso- the accelerating units. The RFQ technology was licensed topes. Here, C has capitalised on the experience of its to the C spin-off ADAM, now part of AVO (Advanced ISOLDE facility, which during the past 50 years has the O n c o t h e r a p y), a n d i s b e i n g u s e d a s a n i nj e c t or for a br e a k- proton ea fro the C S ooster to produce through linear proton therap achine at the copans U d i ff e r e nt i s o t o p e s f r o m 73 c h e m ic a l e le m e nt s for r e s e a rc h a s s e m bl y a n d t e s t i n g c e nt r e at S T FC’s D a r e s b u r y L a b or at or y. ranging fro nuclear phsics to the life sciences. new In 2019 CERN launched the Next Ion Medical Machine facilit, called ISOLDE-MEDICIS, is entirel dedicated to Rise / Fall Time Sampling Rate Amplitude Range Study (NIMMS) to develop cutting-edge a c c e le r at or t e c h- the production of unconventional radioisotopes with the nologies for a new generation of copact and cost-eff ective right properties to enhance the precision of oth patient www.activetechnologies.it Phone: +39 0532 1772145 | E-Mail: [email protected] Designed and Manufactured in Italy 2 CERN COURIER JULY/AUGUST 2021

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FEATURE ALICE ALICE-PHO-GEN-2021-002-10 SDD ALICE Silicon Drift Detectors TRACKS for Science at the Speed of Light Technologically Advanced Silicon Drift Detectors NEW Exceptional Rise Time — Rise times <25 ns TERRITORY Outstanding Throughput — Output count rates >5 Mcps per channel Superior Energy Resolution — Energy resolution <230 eV at 3 Mcps (OCR) Unique Sensor Thickness — Thickness available 0.5 mm, 1.0 mm and 2.0 mm The recently installed, upgraded ALICE inner tracking system is the The VORTEX® range Silicon Drift Detectors, available with a selection of configurations including largest pixel detector ever built and Sensor Thickness — 0.5, 1.0 and 2.0 mm t he fi rst at t he LHC to use monol it h ic 2 active pixel sensors, describe All in Half of the three-layer inner barrel (surrounding the beampipe) and the Active Areas — 50, 65 and 100 mm first layer of the outer barrel (gold) of ALICE’s “ITS2”, along with the new muon Probe Lengths — From 60 to over 600 mm Luciano Musa and Stefania Beolé. for ward tracker (green panel). Sensor Arrays and Designs — Single, Multiple, Planar, Focused n the coming decade, the study of nucleus–nucleus, a l low pp a nd Pb–Pb col l i sion s to b e read out 100 a nd 1000 proton–nucleus and proton–proton collisions at the times more quickly than was possible in previous runs, Environments — Air, vacuum, UHV and He ILHC will offer rich opportunities for a deeper explora- offe r i n g s up e r ior a bi l it y t o m e a s u r e p a r t ic le s at lo w trans- tion of the quark–gluon plasma (QGP). An expected 10-fold verse momenta (see “High impact” figure). Moreover, the Number of Sensors — Single VORTEX® EX and EM SDD increase in the number of lead–lead (Pb–Pb) collisions inner three layers of the ITS2 feature a material budget should both increase the precision of measurements of three times lower than the original detector, which is also — Three VORTEX® ME-3 SDD known probes of the QGP medium as well as give access important for improving the tracking performance at low to ne w one s. B y fo c usi n g on r a re pro b e s do w n to ve r y lo w transverse momentum. — Four VORTEX® ME-4 SDD 2 transverse momentum, such as heavy-flavour particles, W it h it s 10 m of a c t i ve s i l ic on a re a a nd ne a rly 13 billion — Seven VORTEX® ME-7 SDD quarkonium states, real and virtual photons, as well the pixels, the ITS2 is the largest pixel detector ever built. It is study of jet quenching and exotic heavy nuclear states, a lso t he first detec tor at t he LHC to use monol it h ic ac t ive ver y large data samples w ill be required. pixel sensors (MAPS), instead of the more conventional To seize these opportunities, the ALICE collaboration and well-established hybrid pixels and silicon microstrips. Customization and discussions — contact: [email protected] has undertaken a major upgrade of its detectors to increase the event readout, online data processing and record- Change of scale ing capabilities by nearly two orders of magnitude (CERN The particle sensors and the associated readout electron- Courier Ja nu a r y/ Fe br u a r y 2019 p25). T h i s w i l l a l lo w P b –P b ics used for vertexing and tracking detection systems minimum-bias events to be recorded at rates in excess of in particle-physics experiments have very demanding 50 kHz, which is the expected Pb–Pb interaction rate at requirements in terms of granularity, material thickness, the LHC in Run 3, as well as proton–lead (p–Pb) and pro- readout speed and radiation hardness. The development ton–proton (pp) collisions at rates of about 500 kHz and of sensors based on silicon-semiconductor technology 1 M H z, r e s p e c t i v e l y. I n a d d it io n, t h e up g r a d e w i l l i m pr o v e a n d r e a d o ut i nt e g r at e d c i rc u it s b a s e d o n C MOS t e c h n ol- the ability of the ALICE detector to distinguish secondary ogy revolutionised the implementation of such detec- vertices of particle decays from the interaction vertex and tion systems. The development of silicon microstrips to track very low transverse-momentum particles. This and hybrid pixel detectors, already successfully used at will allow measurements of heavy-flavour hadrons and the Large Electron-Positron (LEP) collider, enabled the low-mass dileptons with unprecedented precision and construction of tracking and vertexing detectors that THE AUTHORS down to zero transverse momentum. meet the extreme requirements – in terms of particle Luciano Musa These ambitious physics goals have motivated the rates and radiation hardness – set by the LHC. As a result, CERN and Stefania development of an entirely new inner tracking system, silicon microstrip and pixel sensors are at the heart of Beolé University of Hitachi High-Tech Science America, Inc. www.hitachi-hightech.com/hhs-us/ ITS2. Starting from LHC Run 3 next year, the ITS2 will the particle-tracking systems in most particle-physics Torino and INFN. 20770 Nordhoff St. Chatsworth, CA 91311 Email: [email protected] Tel: +44 747 1086 241 CERN COURIER JULY/AUGUST 2021 29

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FEATURE ALICE FEATURE ALICE ALICE collab. ALICE

3 n-well transistors n-well 10 ALICE ALICE collab.

ALICE collab. diode NMOS PMOS diode z VRST 18 –3 p-well p-well n-well p-well NA ~ 10 cm

VBB ALICE-PHO-GEN-2021-002-11 deep p-well deep p-well inner barrel 2 z outer barrel

h m) 10 e drift μ beam pipe e rϕ rϕ h h e e diffusion h 13 –3 epitaxial layer P– NA ~ 10 cm 10

18 –3 pointing resolution ( substrate P++ NA ~ 10 cm Cylindrical structure Layout of the ITS2 detector showing the ITS 1 (data) inner barrel surrounding the beam pipe and the outer barrel. ITS 2 ALPIDE journeys A schematic cross-section of the ALPIDE chip. When a charged 2 particle traverses the silicon sensor’s active volume, it liberates charge carriers 1 the small collection electrode (about 2 × 2 μ m ), combined (electron and holes) in the semiconductor material. The released charge is then with a circuit that performs sparsified readout within the 10–1 1 10 collected by electrodes (reversed-biased junction diodes) that reveal not only the p (GeV/c) matrix without a free-running clock, keeps the power T ALICE-PHO-ITS-2021-001-30 presence of a particle but also, due to the fine segmentation, its impinging point onto consumption as low as 40 nW per pixel. the sensor. The nature and quantitative behaviour of the charge collection mechanism High impact The pointing resolution as a function of the

are functions of the material properties (doping concentration NA and profile) and transverse momentum for the original ALICE tracker, ITS1, ITS2 structure geometry (thickness of sensitive material, pixel pitch, electrode shape) as well as the (experimental data) and the upgraded ITS2 (simulated) along The ITS2 consists of seven layers covering a radial exten- electric field configuration (electrode potential and geometry) of the sensor. the z-axis and in the transverse (rϕ) plane. sion from 22 to 430 mm with respect to the beamline (see “Cylindrical structure” figure). The innermost three experiments today (see p39). (< 40 mW/cm 2) a n d e x c e l le nt s p at i a l r e s olut io n (~5 μ m) a r e layers form the inner barrel (IB), while the middle two Nevertheless, compromises exist in the implementation perfect for the inner tracker of ALICE. and the outermost two layers form the outer barrel (OB). of this technology. Perhaps the most significant is the In ALPIDE the sensitive volume is a 25 μm-thick layer of The radial position of each layer was optimised to achieve interface between the sensor and the readout electronics, high-resistivity p-type silicon (> 1 kΩ cm) grown epitaxi- the best combined performance in terms of pointing res- which are typically separate components. To go beyond ally on top of a standard (low-resistivity) CMOS wafer (see olution, momentum resolution and tracking efficiency these limitations and construct detection systems with “A L PI DE j o u r n e y s” fi g u r e). T h e e le c t r ic c h a r g e g e n e r ated in the expected high track-density environment of a higher granularity and less material thickness requires by particles traversing the sensitive volume is collected Pb–Pb collision. It covers a pseudo-rapidity range |η| < 1.22 the development of new technology. The optimal way by an array of n–p diodes reverse-biased with a positive for 90% of the most luminous beam interaction region, to achieve this is to integrate both sensor and readout p ot e nt i a l (~1 V) applied on the n-well electrode and a neg- extending over a total surface of 10 m2 and containing electronics to create a single detection device. This is the ative potential (down to a minimum of –6 V) applied to about 12.5 Gpixels with binary readout, and is operated at approach taken with CMOS active pixel sensors (APSs). the substrate (backside). The possibility of varying the room temperature using water cooling. Over the past 20 years, extensive R&D has been carried out reverse-bias voltage in the range 1 to 7 V allows control Given the small size of the ALPIDE (4.5 cm2), sensors are on CMOS APSs, making this a viable option for vertexing over the size of the depleted volume (the fraction of the tiled-up to form the basic detector unit, which is called and tracking detection systems in particle and nuclear sensitive volume where the charge is collected by drift a stave. It consists of a “space-frame” (a carbon-fibre physics, although their performance in terms of radiation due to t he presence of an electric field) and, correspond- mechanical support), a “cold plate” (a carbon ply embed- State of the art Top: the bottom half of the ITS2 inner barrel ready for insertion, hardness is not yet at the level of hybrid pixel detectors. ingly, the charge-collection time. Measurements carried ding two cooling pipes) and a hybrid integrated circuit where the staves of the innermost layer are clearly visible. Bottom: integration test T h e fi r s tlarge-scale application of CMOS APS technology out on sensors with characteristics identical to ALPIDE (HIC) assembly in which the ALPIDE chips are glued and for the ITS2 outer barrel, which proved that the alignment is adequate to avoid in a collider experiment was the STAR PXL detector at have shown an average charge-collection time consist- electrically connected to a flexible printed circuit. An IB interference between the top and bottom halves. Brookhaven’s Relativistic Heavy-Ion Collider in 2014 (CERN ently below 15 ns for a typical reverse-bias voltage of 4 V. HIC and an OB HIC include one row of nine chips and two Courier October 2015 p6). The ALICE ITS2 has benefitted Applying reverse substrate bias to the ALPIDE sensor also rows of seven chips, respectively. The HICs are glued to The process and procedures to build the HICs and staves f r o m s i g n i fic a nt R& D s i n c e t h e n, i n p a r t ic u l a r c o n c e rnig increases the tolerance to non-ionising energy loss to well the mechanical support: 1 HIC for the IB and 8 or 14 HICs are rather complex and time-intensive. More than 10 con- 13 2 the development of a more advanced CMOS imaging sensor, beyond 10 1 MeV neq/cm , which is largely sufficient to for the two innermost and two outermost layers of the OB, struction sites distributed worldwide worked together to named ALPIDE, with a minimum feature size of 180 nm. meet ALICE’s requirements. respectively (see “State of the art” figure). develop the assembly procedure and to build the compo- This has led to a significant improvement in the field of Another important feature of ALPIDE is the use of a p-well Zero-suppressed hit data are transmitted from the staves nents. More than 120 IB and 2500 OB HICs were built using MAPS for single-particle detection, reaching unprece- to shield the full CMOS circuitry from the epitaxial layer. to a system of about 200 readout boards located 7 m away a custom-made automatic module-assembly machine, dented performance in terms of signal/noise ratio, spatial Only the n-well collection electrode is not shielded. The from the detector. Data is transmitted serially with a implementing electrical testing, dimension measurement, resolution, material budget and readout speed. deep p-well prevents all other n-wells – which contain bit-rate up to 1.2 Gb/s over more than 3800 twin-axial integrity inspection and alignment for assembly. A total ALPIDE, circuitry – from collecting signal charge from the epitax- cables reaching an aggregate bandwidth of about 2 Tb/s. of 96 IB staves, enough to build two copies of the three IB which is the ALPIDE sensors ial layer, and therefore allows the use of full CMOS and The readout boards aggregate data and re-transmit it over layers, and a total of 160 OB staves, including 20% spares, result of an ALPIDE, which is the result of an intensive R&D effort consequently more complex readout circuitry in the pixel. 768 optical-fibre links to the first-level processors of the have been assembled. intensive R&D carried out by ALICE over the past eight years, is the build- A LIC E i s t he fi r s t e x p e r i me nt w he re t h i s h a s b e e n u s e d t o combined online/offline (O2) computing farm. The data A large cleanroom was built at CERN for the full detector effort, is the ing block of the ITS2. The chip is 15 × 30 mm2 in area and implement a MAPS with a pixel front-end (amplifier and are then sequenced in frames, each containing the hit assembly and commissioning activities. Here the same building block contains more than half a million pixels organised in 1024 discriminator) and a sparsified readout within the pixel information of the collisions occurring in contiguous time backend system that will be used in the experiment was of the ITS2 columns and 512 rows. Its very low power consumption matrix similar to hybrid sensors. The low capacitance of intervals of constant duration, typically 22 µs. installed, including the powering system, cooling system,

30 CERN COURIER JULY/AUGUST 2021 CERN COURIER JULY/AUGUST 2021 31

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FEATURE ALICE INNOVATION IN MAGNETICS heavy-flavour transport coefficients. A third area where the new ITS will have a major impact is the measurement

ALICE Collab. of electron–positron pairs emitted as thermal radiation during all stages of the heavy-ion c ol l i s io n, w h ic h offe r a n insight into the bulk properties and space–time evolution of the QGP.

More in store The full potential of the ALPIDE chip underpinning the ITS2 is yet to be fully exploited. For example, a variant of ALPIDE explored by ALICE based on an additional low-dose deep n-type implant to realise a planar junction in the epi- taxial layer below the wells containing the CMOS circuitry r e s u lt s i n a muc h f a s t e r c h a r g e c ol le c t io n a n d s i g n i fic a nt l y CRYOMAG improved radiation hardness, paving the way for sensors • Magnetic field monitoring in cryostats and that are much more resistant to radiation. other low temperature environments Further improvements to MAPS for high-energy physics detectors could come by exploiting the rapid progress in • Operating temperature down to 2K imaging for consumer applications. One of the features • Measuring ranges of ±70μT and ±100μT offered recently by CMOS imaging sensor technologies, Into the future Conceptual design of the ITS3, where all silicon layers (green) called stitching, will enable a new generation of MAPS with Independent element version coming soon surround the beam pipe (orange) supported by carbon-foam support rings (grey). an area up to the full wafer size. Moreover, the reduction i n t h e s e n s or t h ic k n e s s t o a b o ut 30–40 μ m o p e n s t h e d o or full readout and trigger chains. Staves were installed on to large-area curved sensors, making it possible to build the mechanical support structures to form layers, and the a cylindrical layer of silicon-only detectors with a further

layers are assembled in half-barrels, IB (layers 0, 1 and 2) s i g n i fic a nt r e d uc t io n i n t h e m at e r i a l t h ic k n e s s. T h e A LICE T: +44 (0)1993 706565 • E: [email protected] • W: bartington.com top and bottom and OB (layers 3, 4, 5 and 6) top and bottom. collaboration is already preparing a new detector based on Each stave is then connected to power-supply and readout these concepts, which consists of three cylindrical layers systems. The commissioning campaign started in May based on curved wafer-scale stitched sensors (see “Into the 2019 to fully characterise and calibrate all the detector f ut u r e” fi g u r e). T h i s n e w v e r t e x d e t e c t or w i l l b e i n stalled components, and installations of both the OB and IB were during Long Shutdown 3 towards the middle of the decade, CERN Courier Advert Jun 2021 V2.indd 1 08/06/2021 9:55 am RELIABLE completed in May this year. replacing the three innermost layers of the ITS2. With the first detection layer closer to the interaction point (from Physics ahead 23 to 18 mm) and a reduction in the material budget close UNDER ALL After nearly 10 years of R&D, the upgrade of the ALICE to the interaction point by a factor of six, the new vertex experimental apparatus – which includes an upgraded detector will further improve the tracking precision and CONDITIONS. time projection chamber, a new muon forward tracker, efficienc y at low transverse momentum. a new fast-interaction trigger detector, forward diffrac- The technologies developed by ALICE for the ITS2 detec- Heading into the unknown to open new horizons tion detector, new readout electronics and an integrated tor are now being used or considered for several other online–offline computing system – is close to completion. applications in high-energy physics, including the vertex demands reliable tools. Help turn your resarch Most of the new or upgraded detectors, including the ITS2, detector of the sPHENIX experiment at RHIC, and the inner goals into reality. have already been installed in the experimental area and tracking system for the NICA MPD experiment at JINR. The Vacuum valve solutions and bellows the global commissioning of the whole apparatus will be t e c h n olo g y i s a l s o b e i n g a p pl ie d t o a r e a s o ut s id e o f t h e fie ld, from VAT provide unfailing reliability completed this year, well before the start of Run 3, which including in medical and space applications. The Bergen and enhanced process safety – is scheduled for the spring of 2022. pCT collaboration and INFN Padova’s iMPACT project, for under all conditions. T h e s i g n i fic a nt e n h a n c e m e nt s t o t h e p e r for m a n c e o fthe example, are developing novel ALPIDE-based devices for ALICE detector will enable detailed, quantitative charac- clinical particle therapy to reconstruct 3D human body terisation of the high-density, high-temperature phase of images. The HEPD02 detector for the Chinese–Italian strongly interacting matter, together with the exploration CSES-02 mission, meanwhile, includes a charged-particle The significant of new phenomena. The ITS2 is at the core of this pro- tracker made of three layers of ALPIDE sensors that repre- gramme. With improved pointing resolution and tracking sents a pioneering test for next-generation space missions. enhancements efficiency at low transverse momentum, it will enable the Driven by a desire to learn more about the fundamental laws to the determination of the total production cross-section of of nature, it is clear that advanced silicon-tracker technol- performance the charm quark. This is fundamental for understanding ogy continues to make an impact on wider society, too.  of the ALICE the interplay between the production of charm quarks in detector will the initial hard scattering, their energy loss in the QGP Further reading enable the and possible in-medium thermal production. Moreover, B Abelev et al. 2014 J. Phys. G 41 087002. exploration the ITS2 will also make it possible to measure a larger G Aglieri et al. 2013 JINST 8 C12041. of new number of different charmed and beauty hadrons, includ- G Aglieri et al. 2021 Nucl. Instrum. Meth. A 988 164859. phenomena ing baryons, opening the possibility for determining the W Snoeys et al. 2017 Nucl. Instrum. Meth. A 871 90.

32 CERN COURIER JULY/AUGUST 2021 www.vatvalve.com

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FEATURE LHC EXPERIMENT UPGRADES STATE-OF-THE-ART TRACKING FOR HIGH LUMINOSITIES

Each at different stages of development depending on their implementation schedules and operating conditions, the tracking systems of the ATLAS, LHCb and CMS e x p er i ment s, l i ke t hat for A LICE, a re undergoi ng complete replacement s to prepa re for t he e x t reme op er at i ng cond it ions of f ut ure LHC r uns, e x pla i ns M at t he w Cha l mers.

Towards the CMS phase-2 pixel detector LHCb’s all-new VELO takes shape ATLAS ITk pixel detector on track

The original silicon pixel detector preparation for the High-Luminosity LHCb’s Vertex Locator (VELO) has hef k n/Ni aa r K M isco nc a Fr O The ATLAS collaboration upgraded O-201902-038-2 T N-PHO CER for CMS – comprising three barrel LHC (HL-LHC). This Phase-2 pixel played a pivotal role in the experiment’s its original pixel detector in 2014, layers and two endcap disks – was detector will need to cope with a flavour-physics programme. Contributing adding an innermost layer to create designed for a maximum instantaneous pile-up and hit rate eight times to triggering, tracking and vertexing, and a four-layer device. The new layer luminosity of 1034 cm–2 s–1 and a higher than before, and with a trigger with a geometry optimised for particles contained a much smaller pitch, maximum average pile-up of 25. rate and radiation dose 7.5 and 10 traveling close to the beam direction, its 3D sensors at large angles and

Following LHC upgrades in 2013–2014, times higher, respectively. To meet 46 orthogonal silicon-strip half-disks CO2 cooling, and the pixel tracker it was replaced with an upgraded system these extreme requirements, the CMS have enabled the collaboration to pursue will continue to serve ATLAS (the CMS Phase-1 pixel detector) in collaboration, in partnership with major results. These include the 2019 throughout LHC Run 3. Like CMS, 2017 to cope with higher instantaneous ATLAS via the RD53 collaboration, discovery of CP violation in charm using the luminosities. With a lower mass and is developing a next-generation world’s largest reconstructed samples of The device will have a an additional barrel layer and endcap hybrid-pixel chip utilising 65 nm charm decays, a host of matter–antimatter In production Wouter Hulsbergen and Krista De Roo assemble VELO modules at Nikhef (left), total of 5.1 Gpixels – disk, it was an evolutionary upgrade CMOS technology. The overall system asymmetry measurements and rare-decay while Stefano De Capua is shown undertaking parallel work at the University of Manchester (right). y s i nsk y z Byc W hef k n/Ni aa r K M maintaining the well-tested key is much bigger than the Phase-1 searches, and the recent hints of lepton 55 times more than ATLAS Collab. features of the original detector while device (~5 m2 compared to 1.75 m2) non-universality in B decays. the current one enabling higher-rate capability, with vastly more read-out channels Placing the sensors as close as possible improved radiation tolerance and more (~2 billion compared to 120 million). to the primary proton–proton interactions robust tracking. During Long Shutdown With six-times smaller pixels, requires the whole VELO system to sit inside the collaboration has long been 2, maintenance work on the Phase-1 increased detection coverage, reduced the LHC vacuum pipe (separated from the working towards the replacement device included the installation of a new material budget, a new readout chip primary vacuum by a 1.1 m-long thin-walled of the full inner tracker during the innermost layer (see image, below) to to enable a lower detection threshold, “RF foil”), and a mechanical system to next long shutdown expected in enable the delivery of high-quality data and a design that continues to allow move the disks out of harm’s way during the 2025, in preparation for HL-LHC until the end of LHC Run 3. easy installation and removal, the injection and stabilisation of the beams. After operations. The innermost layers of During the next long shutdown, state-of-the-art Phase-2 pixel more than a decade of service witnessing the this state-of-the-art all-silicon ATLAS pixels Top: a prototype of the scheduled for 2025, the entire detector will serve CMS well into the passage of some 1026 protons, the original tracker, called the ITk, will be built ATLAS ITk pixel detector, showing sensors tracker detector will be replaced in HL-LHC era. VELO is now being replaced with a new from pixel detectors with an area tilted with respect to the beam axis to

u z But E one to prepare for a factor-five increase in Fine structure Left: a silicon wafer containing “race track” microchannels (overlaid for almost 10 times larger than that of the improve tracking performance while 2 luminosity for LHCb in LHC Run 3. illustration only), in which evaporative CO2 circulates to cool the detector. Right: inspecting current device. With 13 m of active reducing the total silicon area. Bottom: a The entirety of the new VELO will be read the thickness of the upgraded RF foil that will enclose the new VELO within the LHC vacuum. silicon across five barrel layers and 3D silicon sensor developed for the pixel out at a rate of 40 MHz, requiring a huge two end caps, the pixel detector will region of the ATLAS inner detector. data bandwidth: up to 20 Gbits/s for the located even closer to the interaction point which provides cooling, services and contribute to precision tracking up hottest ASICs, and 3 Tbit/s in total. Cooling (5.1 mm versus the previous 8.2 mm for the vacuum, is now under way, with installation to a pseudorapidity |η| = 4, with the flowing inthin-walled pipes. The using the minimum of material is another first measured point), which requires the in LHCb scheduled to start in August. The innermost two layers expected to be device will have a total of 5.1 Gpixels major challenge. The upgraded VELO will RF foil to sit just 3.5 mm from the beam and VELO Upgrade I is expected to serve LHCb replaced a few years into the HL-LHC (55 times more than the current be kept at –20° via the novel technique of 0.9 mm from the sensors. The production of throughout Run 3 and Run 4. Looking era, and the outermost layers designed one), and the very high expected

evaporative CO2 circulating in 120 × 200 µm the foil was a huge technical achievement. further to the future, the next upgrade will to last the lifetime of the project. HL-LHC data rates, especially in the channels within a silicon substrate (see It was machined from a solid-forged require the detector to operate with a huge Most of the detector will use planar innermost layers, will require the “Fine structure”, left). The harsh radiation aluminium block with 98% of the material jump in luminosity, where vertexing will silicon sensors, with 3D sensors development of new technologies environment also demands a special ASIC, removed and the final shape machined to a pose a significant challenge. Proposals (which are more radiation-hard for high-bandwidth transmission the VeloPix, which has been developed thickness of 250 µm, with further chemical under consideration include a new “4D” and less power-hungry) in the and handling. The ITk pixel detector with the CERN Medipix group and will etching taking it to just 100 µm (see “Fine pixel detector with time-stamp information innermost layer. Like the CMS is now in the final stages of R&D and Present and future Top: the new allow the detector to operate a much more structure”, right). per hit, which could conceivably be achieved Phase-2 pixel upgrade, the sensors moving into production. After that, innermost layer of the CMS tracker

C MS col lab. efficient trigger. To cope with increased Around half of the VELO-module by moving to a smaller CMOS node. At this will be read out by new chips being the final stages of integrating the being installed in January 2021. occupancies at higher luminosity, the production is complete, with the work stage, however, the collaboration is actively developed by the RD53 collaboration, subdetectors assembled in ATLAS Left: how the CMS Phase-2 pixel original silicon strips have been replaced shared between labs in the UK and the investigating all options, with detailed with support structures made of institutes worldwide will take place detector, called “Inner Tracker”, with pixels. The new sensors (in the form Netherlands (see “In production”). technical design reports expected towards low-mass carbon materials and on the surface at CERN before final will look. of rectangles rather than disks) will be Assembly of the 52 modules into the “hood”, the middle of the decade. cooling provided by evaporative CO2 installation underground.

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FEATURE PIXEL DETECTORS

simulation case study Analyze laser- material interaction TRACKING THE RISE with simulation OF PIXEL DETECTORS Laser-material interaction, and the subsequent heating, is often studied with simulation using one of several modeling techniques. To select the most suitable approach, you can From their beginnings at CERN half a century ago, writes Chris Damerell, silicon pixel use information such as the material’s optical properties, detectors for particle tracking have blossomed into a vast array of beautiful creations the relative sizes of the objects to be heated, and the laser wavelength and beam characteristics as a guide. For the that have driven numerous discoveries, with no signs of the advances slowing down. simulation, you can use COMSOL Multiphysics®. M Hoch/CMS-PHO-TRACKER-2014-001-3M learn more comsol.blog/laser-heating

The COMSOL Multiphysics® software is used for simulating designs, devices, and processes in all fields of engineering, manufacturing, and scientific research.

Pixel perfect The original central and forward pixel detector of the CMS inner tracker, since replaced with a more advanced system.

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FEATURE PIXEL DETECTORS FEATURE PIXEL DETECTORS

THE AUTHOR ixel detectors have their roots in photography. Up physics experiments. The evolution of these device types is Pixel architectures Chris Damerell until 50 years ago, every camera contained a roll intertwined to such an extent that any attempt at historical Rutherford P of film on which images were photochemically accuracy, or who really invented what, would be beyond Appleton recorded with each exposure, after which the completed the capacity of this author, for which I humbly apologise. Laboratory (RAL). roll was sent to be “developed” to finally produce eagerly Space constraints have also led to a focus on the detec- awaited prints a week or so later. For decades, film also tors themselves, while ignoring the exciting work in ROIC played a big part in particle tracking, with nuclear emul- development, cooling systems, mechanical supports, not sions, cloud chambers and bubble chambers. The silicon to mention the advanced software for device simulation, c h i p, fi r s t u n v e i le d t o t h e w orld i n 1961, w a s t o c h a n g ethis the simulation of physics performance, and so forth. picture forever. B y t h e 1970 s, n e w d e s i g n s o f s i l ic o n c h i p s w e r e i n v e nt e d CCD design inspiration that consisted of a 2D array of charge-collection sites or The early developments in CCD detectors were disregarded “picture elements” (pixels) below the surface of the silicon. by the particle-detector community. This is because gas- During the exposure time, an image focused on the surface eous drift chambers, with a precision of around 100 μm, Illustrations of a CCD (left), MAPS (middle) manipulating the gate voltages so that the image electronics. The simplest readout is “rolling g e n e r at e d e le c t r o n–h ole p a i r s v i a t h e p h o t o e le c t r ic e ffe c t were thought to be adequate for all tracking applications. and hybrid chip (right). The first two typically is shifted down, one row at a time. Charges from shutter”, in which peripheral logic along the in the underlying silicon, with the electrons collected as However, the 1974 prediction by Gaillard, Lee and Ros- contain 1 k × 1 k pixels, up to 4 k × 4 k or beyond the bottom row are tipped into the linear readout chip edge addresses rows in turn, and analogue signal information in the pixels. These chips came in two ner that particles containing charm quarks “might have by “stitching”, with an active layer thickness register, within which they are transferred, all signals are transmitted by column lines to forms: the charge-coupled device (CCD) and the monolithic lifetimes measurable in emulsions”, followed by the dis- (depleted) of about 20 µm and a highly doped together in the orthogonal direction, towards peripheral logic at the bottom of the imaging active pixel sensor (MAPS) – more commonly known com- covery of charm in 1975, set the world of particle-physics bulk layer back-thinned to around 100 µm, the output node. As each signal charge reaches area. Unlike in a CCD, the signal charges never mercially as the CMOS image sensor (CIS). Willard Boyle instrumentation ablaze. Many groups with large budgets enabling a low-mass tracker, even potentially the output node, it modulates the voltage on move from their “parent” pixel. and George Smith of Bell Labs in the US were awarded the tried to develop or upgrade existing types of detectors to bent into cylinders round the beampipe. the gate of the output transistor; this is sensed, In the hybrid chip, like a MAPS, signals are read Nobel Prize for Physics in 2009 for inventing the CCD. meet the challenge: bubble chambers became holographic; The CCD (where I is the imaging area, R the and transmitted off-chip as an analog signal. out by scanning circuitry. However, the charges In a CCD, the charge signals are sequentially trans- drift chambers and streamer chambers were pressurised; readout register, TG the transfer gate, CD the In a MAPS chip, pixellisation is implemented are generated in a separate silicon layer that is ferred to a single on-chip output circuit by applying voltage silicon microstrips became finer-pitched, etc. collection diode, and S, D, G the source, drain by orthogonal channel stops and signal charges connected, pixel by pixel, to a readout integrated pulses to the overlying electrode array that defines the pixel The ACCMOR Collaboration (Amsterdam, CERN, Cracow, and gate of the sense transistor) is pixellised are sensed in-pixel by a tiny front-end circuit. Bump-bonding interconnection structure. At the output circuit the charge is converted to a Munich, Oxford, RAL) had built a powerful multi-particle in the I direction by conducting gates. Signal transistor. Within a depth of about 1 µm below technology is used to keep up with pixel voltage signal to enable the chip to interface with external spectrometer, operating at CERN’s Super Proton Syn- charges are shifted in this direction by the surface, each pixel contains complex CMOS miniaturisation. (Image credits: RAL; PSI) circuitry. In the case chrotron, to search for hadronic production of the During the past 40 years, of the MAPS, each recently-discovered charm particles, and make the first pixel has its own measurements of their lifetimes. We in the RAL group plus a beautiful assembly of Cherenkov hodoscopes from Z0 decays yielded rich physics. Highlights included very silicon sensors have charge-integrating picked up the idea of CCDs from astronomers at the Uni- the Munich group, proved to be a D+→ K+π+π– event. detailed studies of an enormous sample of gluon jets from 0 – detection cir- versity of Cambridge, who were beginning to see deeper It was more challenging to develop a CCD-based vertex Z → b b g events, with cleanly tagged b jets at LEP, and Ac, transformed particle cuitry and a volt- into space than was possible with photographic film (see detector for the SLAC Large Detector (SLD) at the SLAC the parity-violation parameter in the coupling of the Z0 to tracking in high-energy age signal is again le f t fi g u r e i n “P i x e l a rc h it e c t u r e s” p a n e l). T h e br i l l i a ntCD Linear Collider (SLC), which became operational in 1989. c-quarks, at SLD. However, the most exciting discovery sequentially read developers in David Burt’s team at the EEV Company in The level of background radiation required a 25 mm-radius of that era was the top quark at Fermilab, in which the physics experiments out from each by Chelmsford (now Teledyne e2v) suggested designs that we beam pipe, and the physics demanded large solid-angle SVX microstrip detector of the CDF detector played an on-chip switching could try for particle detection, notably to use epitaxial sili- coverage, as in all general-purpose collider detectors. The e s s e nt i a l p a r t (s e e “To p d e t e c t or” fi g u r e). T h i s t r i g g e r ed or “scanning” cir- con wafers with an active-layer thickness of about 20 μ m. A t physics case for SLD had been boosted by the discovery a paradigm shift. Before then, vertex detectors were an cuitry. Both archi- a collaboration meeting in Cracow in 1978, we demonstrated in 1983 that the lifetime of particles containing b quarks “optional extra” in experiments; afterwards, they became tectures followed via simulations that just two postage-stamp-sized CCDs, was longer than for charm, in contrast to the theoretical obligatory in every energy frontier detector system. rapid development paths, and within a couple of decades placed 1 and 2 cm beyond a thin target, could cover the expectation of being much shorter. So the case for deploying had completely displaced photographic film in cameras. whole spectrometer aperture and might be able to deliver high-quality vertex detectors at SLC and LEP, which were Hybrid devices For the consumer camera market, CCDs had the initial high-quality topological reconstruction of the decays of under construction to study Z0 decays, was indeed com- While CCDs pioneered the use of silicon pixels for precision lead, which passed to MAPS by about 1995. For scientific charm particles with expected lifetimes of around 10–13 s. p e l l i n g (s e e “Ve r t e x i n g” fi g u r e). A l l fo u r L E P e x p e r i m e nts tracking, their use was restricted by two serious limi- imaging, CCDs are preferred for most astronomical appli- We still had to demonstrate that these detectors could be employed a silicon-microstrip vertex detector. tations: poor radiation tolerance and long readout time cations (most recently the 3.2 Gpixel optical camera for the m a d e e ffic ie nt for p a r t ic le d e t e c t io n. W it h a s m a l l t e le s cope Early in the silicon vertex-detector programme, e2V (tens of ms due to the need to transfer the charge signals Vera Rubin Observatory), while MAPS are the preferred comprising three CCDs in the T6 beam from CERN’s Proton perfected the art of “stitching” reticles limited to an area pixel by pixel through a single output circuit). There was option for fast imaging such as super-resolution micros- Synchrotron we established a hit efficiency of more than of 2 × 2 cm2, to make large CCDs (8 × 1.6 cm2 for SLD). This clearly a need for pixel detectors in more demanding envi- copy, cryoelectron microscopy and pioneering studies of 99%, a track measurement precision of 4.5 μm i n x a nd y, enabled us to make a high-performance vertex detector ronments, and this led to the development of hybrid pixel protein dynamics at X-ray free-electron lasers. Recent and two-track resolut ion of 40 μm. Nothing like this had that operated from 1996 until SLD shut down in 1998, and detectors. The idea was simple: reduce the strip length of CMOS imagers with very small, low-capacitance pixels been seen before in an electronic detector. Downstream which delivered a cornucopia of heavy-flavour physics well-developed microstrip technology to equal its width, achieve sufficiently low noise to detect single electrons. of us, in the same week, a Yale group led by Bill Willis from Z0 d e c a y s (s e e “P io n e e r i n g pi x e l s” fi g u r e). D u r i n g t h is and you had your pixel sensor. However, microstrip detec- A third member of the family is the hybrid pixel detector, obtained signals from a small liquid-argon calorimeter. time, the LEP beam pipe, limited by background to 54 mm tors were read out at one end by ASIC (application-specific which is MAPS-like in that the signals are read out by A bottle of champagne was shared! radius, permitted its experiments’ microstrip-based vertex integrated circuit) chips having their channel pitch matched scanning circuitry, but in which the charges are generated It was then a simple step to add two CCDs to the ACCMOR detectors to do pioneering b physics. But it had reduced to that of the strips. For hybrid pixels, the ASIC readout in a separate silicon layer that is connected, pixel by pixel, spectrometer and start looking for charm particles. During capability for the more elusive charm, which was shorter required a front-end circuit for each pixel, resulting in to a readout integrated circuit (ROIC). 1984, on the initial shift, we found our first candidate (see lived and left fewer decay tracks. modules with the sensor chip facing the readout chip, During the past 40 years, these devices (along with their “First charm” figure), which, after adding the information Between LEP with its much higher luminosity and with electrical connections made by metal bump-bonds silicon-microstrip counterparts, to be described in a later from the downstream microstrips, drift chambers (with SLD with its small beam pipe, state-of-the-art vertex (see right figure in “Pixel architectures” panel). The use issue) have transformed particle tracking in high-energy two large aperture magnets for momentum measurement), detector and highly polarised electron beam, the study of of relatively thick sensor layers (compared to CCDs) com-

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FEATURE PIXEL DETECTORS FEATURE PIXEL DETECTORS ACCMOR Collab. ACCMOR J Pequenao/CERN-GE-0803013-02 SLD collab. SLD Collab. ALICE collab. ALICE

+ e– e First charm The first charm decay seen with a silicon detector by the ACCMOR Collaboration in 1984, using a thin target followed by CCDs at 1 and 2 cm beyond (view along beam IP direction). The decay tracks were clearly recognised in the online display in just 1 mm2 of CCD area.

Vertexing An ideal vertex detector at an e +e– collider, where space-points component chips. The disadvantages include a complex measured with few-micron precision distinguish between tracks from the and expensive assembly procedure, high power dissipation primary, secondary and tertiary vertices (green, blue and red). due to large node capacitance, and more material than is Pioneering pixels Left: half of the SLD vertex detector, consisting of 307 Mpixels, three barrels and a pixel size of 20 × 20 × 20 μm 3. Each ladder of 16 cm desirable for a tracking system. Thanks to the sustained active length contains two 8 cm-long stitched CCDs. Top right: CGI of the original ATLAS pixel detector, comprising 92 Mpi xels (50 × 400 μm 2 for the pensated for the higher node capacitance associated with e ffor t s o f m a n y e x p e r t s, a n i m pr e s s i v e c ol le c t io n o f hybrid external layers and 50 × 250 μm 2 for the innermost layer). Bottom right: simulated tracks in the MAPS-based ALICE ITS2, containing 12 .5 Gpi xels and a the hybrid front-end circuit. pixel tracking detectors has been brought to completion in 10 m 2 active area (see p29). To offer a sense of scale, the entire SLD vertex detector would fit within the innermost layer of the ATLAS pixel detector. Although the idea was simple, its implementation a number of detector facilities. As vertex detectors, their involved a long and challenging programme of engineer- greatest triumph has been in the inferno at the heart of The latest experiment to upgrade from strips to pixels is is an adventurous long-term R&D programme, and LHCb ing at the cutting edge of technology. This had begun by ATLAS and CMS where, for example, they were key to the LHCb, which has an impressive track record of b and charm retain a fallback option with timing layers downstream – about 1988, when Erik Heijne and colleagues in the CERN recent measurement of the branching ratio for H → b b. physics. Its adventurous Vertex Locator (VELO) detector of the VELO, if required. microelectronics group had the idea to fit fullnuclear-pulse has 26 disks along the beamline, equipped with orthogo- processing electronics in every pixel of the readout chip, Facing up to the challenge nally oriented r and ϕ microstrips, starting from inside the Monolithic active pixels with additional circuitry such as digitisation, local memory The high-luminosity upgrade to the LHC (HL-LHC) is beampipe about 8 mm from the LHC beam axis. LHCb has Being monolithic, the architecture of MAPS is very similar and pattern recognition on the chip periphery. With a 3 μm placing severe demands on ATLAS and CMS, none more collected the world’s largest sample of charmed hadrons, t o t h at o f CC D s (s e e m id d le fi g u r e i n “P i x e l a rc h it e c t u r e s” feature size, they were obliged to begin with relatively so than developing even more powerful hybrid vertex and with the VELO has made a number of world-leading panel). The fundamental difference is that in a CCD, the large pixels (75 × 500 μm), and only about 80 transistors detectors to accommodate a “pileup” level of 200 events measurements including the discovery of CP violation in signal charge is transported physically through some cen- per pixel. They initiated the RD19 collaboration, which per bunch crossing. For the sensors, a 3D variant invented charm. LHCb is now statistics-limited for many rare decays timetres of silicon to a single charge-sensing circuit in the eventually grew to 150 participants, with many pioneering by Sherwood Parker has adequate radiation hardness, and and will ramp up its event samples with a major upgrade corner of the chip, while in a MAPS the communication developments over a decade, leading to successful detec- may provide a more secure option than the traditional implemented in two stages (see p36). between the signal charge and the outside world is via tors in at least three experiments: WA97 in the Omega planar pixels, but this question is still open. 3D pixels have For t he fi r st upg r ade, due to b e g i n op er at ion ea rly ne x t in-pixel electronics, with metal tracks to the edge of the Spectrometer; NA57; and forward tracking in DELPHI. As already proved themselves in ATLAS, for the insertable year, the luminosity will increase by a factor of up to five, chip. The MAPS architecture looked very promising from the RD19 programme developed, the steady reduction in B layer (IBL), where the signal charge is drifted trans- and the additional pattern recognition challenge will be the beginning, as a route to solving the problems of both feature size permitted the use of in-pixel discriminators versally within the pixel to a narrow column of n-type addressed by a new pixel detector incorporating 55 μm CCDs and hybrid pixels. With respect to CCDs, the radiation and fast shapers that enhanced the noise performance, silicon that runs through the thickness of the sensor. pixels and installed even closer (5.1 mm) to the beam axis. tolerance could be greatly increased by sensing the signal

even at high rates. This would be essential for operation of But for HL-LHC, the innermost pixels need to be at least The pixel detector uses evaporative CO2 microchannel cool- charge within its own pixel, instead of transporting it over large hybrid pixel systems in harsh environments, such as five times smaller in area than the IBL, putting extreme ing to allow operation under vacuum. LHCb will double its thousands of pixels. The readout speed could also be dra- ATLAS and CMS at the LHC. RD19 initiated a programme of pressure on the readout chip. The RD53 collaboration led by efficiency by removing the hardware trigger and reading matically increased by in-pixel amplitude discrimination, radiation hardness by design (enclosed-gate transistors, CERN has worked for years on the development of an ASIC out the data at the beam-crossing frequency of 40 MHz. followed by sparse readout of only the hit pixels. With g u a rd r i n g s, e t c), w h ic h w a s f u r t h e r d e v e lo p e d a n d br o a d l y using 65 nm feature size, which enables the huge amount The new “VeloPix” readout chip will achieve this with respect to hybrid pixel modules, the expense and compli- An impressive disseminated by the CERN microelectronics group. These of radiation-resistant electronics to fit within the pixel readout speeds of up to 20 Gb/s, and the software trigger cations of bump-bonded assemblies could be eliminated, collection of design techniques are now used universally across the LHC area, reaching the limit of 50 × 50 μm2. Assembling these will select heavy-flavour events based on full event recon- and the tiny node capacitance opened the possibility of hybrid pixel detector systems. There is still much to be learned, and delicate modules, and dealing with the thermal stresses struction. For the second upgrade, due to begin in about much thinner active layers than were needed with hybrids. tracking advances to a smaller feature size bring new opportunities associated with the power dissipation in the warm ASICs 2032, the luminosity will be increased by a further factor MAPS have emerged as an attractive option for a number but also surprises and challenges. mechanically coupled to the cold sensor chips, is still of 7.5, allowing LHCb to eventually accumulate 10 times its of future tracking systems. They offer small pixels where detectors has The advantages of the hybrid approach include the abil- a challenge. These pixel tracking systems (comprising current statistics. Under these conditions, there will be, needed (notably for inner-layer vertex detectors) and thin been brought ity to choose almost any commercial CMOS process and five layers of barrel and forward trackers) will amount to on average, 40 interactions per beam crossing, which the layers throughout the detector volume, thereby minimising to completion combine it with the sensor best adapted to the application. about 6 Gpixels – seven times larger than before. Beyond collaboration plans to resolve by enhanced timing preci- multiple scattering and photon conversion, both in barrels in a number This can deliver optimal speed of parallel processing, and the fifth layer, conditions are sufficiently relaxed that sion (around 20 ps) in the VELO pixels. The upgrade will and endcaps. Excess material in the forward region of track- of detector radiation hardness as good as can be engineered in the two microstrip tracking will still be adequate. require both an enhanced sensor and readout chip. This ing systems such as time-projection and drift chambers, facilities

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FEATURE PIXEL DETECTORS FEATURE PIXEL DETECTORS Fermilab G Future Linear Colliders held in March, the SiD concept Deptuch/BNL micro-lenses group announced that they will switch to a MAPS-based sensor tier Tech Insights tracking system. R&D for vertexing at the ILC is also being TSV colour filters revived, including the possibility of CCDs making a come- deep trench isolation back with advanced designs from the KEK group led by DBI channel stops Yasuhiro Sugimoto. 7.8 μm imaging tier The most ambitious goal for MAPS-based detectors is numerous metal layers for the inner-layer barrels at ATLAS and CMS, during the second phase of the HL-LHC era, where smaller pixels would bond line wafer-to-wafer bond provide important advantages for physics. At the start of analogue tier copper–copper high-luminosity operation, these layers will be equipped 2 bond (DBI) bonds with hybrid pixels of 25 1 0 0 μ m and 1 5 0 μ m active thickness, ROIC image signal × line processing (ISP) tier the pixel area being limited by the readout chip, which is digital tier based on a 65 nm technology node. Encouraging work led by TSV numerous the CERN ATLAS and microelectronics groups and the Bonn bump metal layers Top detector Bert Gonzalez with the SVX microstrip vertex group is underway, and could result in a MAPS option of bonding detector of the CDF experiment at the Tevatron in 1993, which 25 × 2 5 μ m 2, requiring an active-layer thickness of only about transistors was instrumental in the co-discovery of the top quark. 2 0 μ m , using a 2 8 n m technology node. The improvement Stacking for physics Functional sketch (not to scale) of a Fermilab/BNL stacked in tracking precision could be accompanied by a substan- pixel detector with three layers: a sensor tier (300 μm thick, for efficient X-ray Up close SEM view of a slice through the imaging region of a stacked Sony CMOS image lo c at e d i n a b u r ie d c h a n n e l d e e p e r t h a n t h e c u r r e nt flo w i n g tial reduction in power dissipation. The four-times greater response), an analogue tier and a digital signal-processing tier (each 15 μm thick). sensor or CIS. The imaging wafer has been thinned to around 6 µm, while the ISP wafer in the sense transistor. As Belle II pushes to even higher pixel density would be more than offset by the reduction in Direct-bond interconnects (DBIs) and through-silicon vias (TSVs) of dimensions is much thicker, to provide the required stiffness. The peripheral structures, including luminosity, it is not yet clear which technology will deliver operating voltage, plus the much smaller node capacitance. 1 × 6 µm provide inter-tier electrical connections. the numerous electrical connections between the two wafers (using direct-bond the required radiation hardness. This route could provide greatly enhanced vertex detector interconnects (DBIs) and through-silicon vias), are outside the field of view. The small collection electrode of the standard MAPS pixel performance at a time when the hybrid detectors will be silicon are stacked and interconnected. The processing presents a challenge in terms of radiation hardness, since coming to the end of their lives due to radiation damage. technique, in which wafers are bonded face-to-face, with with their heavy endplate structures, has in the past led to it is not easy to preserve full depletion after high levels of However, this is not yet guaranteed, and an evolution to electrical contacts made by direct-bond interconnects and poor track reconstruction efficiency, loss of tracks due to b u l k d a m a g e. A n i m p or t a nt i n it i at i v e t o o v e rc o m e t h i s w a s stacked devices may be necessary. A great advantage of through-silicon vias, is now a mature technology and is in secondary interactions, and excess photon conversions. In i n it i at e d i n 2007 b y Iv a n P e r ić o f K I T, i n w h ic h t h e c ol le c t io n moving to monolithic or stacked devices is that the complex the hands of leading companies such as Sony and Samsung. colliders at the energy frontier (whether pp or e+e–), however, electrode is expanded to cover most of the pixel area, below processes are then in the hands of commercial foundries The CMOS imaging chips for phone cameras must be one interesting events for physics are often multi-jet, so there the level of the CMOS electronics, so the charge-collection that routinely turn out thousands of 12 inch wafers per week. of the most spectacular examples of modern engineering are nearly alw ays one or more jets in t he for w ard region. p at h i s muc h r e d uc e d. I m pr e s s i v e f u r t h e r d e v e lo p m e nt s h a v e (see “Up close” figure). T h e fi r s t M A P S d e v ic e s c o nt a i n e d l it t le m or e t h a n acol- been made by groups at Bonn University and elsewhere. This High-speed and stacked Commercial CMOS image sensor development is a major lection diode, a front-end transistor operated as a source approach has achieved high radiation resistance with the During HL-LHC operations there is a need for ultra-fast growth area, with approximately 3000 patents per year. fol lo w e r, r e s e t t r a n s i s t or a n d a d d r e s s i n g lo g ic. T h e y n e e d e d ATLASpix prototypes, for instance. However, the standard tracking devices to ameliorate the pileup problems in ATLAS, In future these developers, advancing to smaller-node only relaxed charge-collection time, so diffusive collec- MAPS approach with small collection electrode may be CMS and LHCb. Designs with a timing precision of tens chips, will add artificial intelligence, for example to take tion sufficed. Sherwood Parker’s group demonstrated tunable to achieve the required radiation resistance, while of picoseconds are advancing rapidly – initially low-gain a number of frames of fast-moving subjects and deliver their capability for particle tracking in 1991, with devices preserving the advantages of superior noise performance avalanche diodes, pioneered by groups from Torino, Bar- the best one to the user. Imagers under development for pr o c e s s e d i n t h e C e nt r e for I nt e g r at e d St ud ie s at St a n ford, due to the much lower sensor capacitance. Both approaches celona and UCSC, followed by other ultra-fast silicon pixel the automotive industry include those that will operate operating in a Fermilab test beam. In the decades since, have strong backing from talented design groups, but the devices. There is a growing list of applications for these in the short-wavelength infrared region, where silicon is advances in the density of CMOS digital electronics have eventual outcome is unclear. devices. For example, ATLAS will have a layer adjacent to the still sensitive. In this region, rain and fog are transparent, enabled designers to pack more and more electronics into electromagnetic calorimeter in the forward region, where so a driverless car equipped with the technology will be each pixel. For fast operation, the active volume below Advanced MAPS the pileup problems will be severe, and where coarse gran- able to travel effortlessly in the worst weather conditions. the collection diode needs to be depleted, including in the Advanced MAPS devices were proposed for detectors at ularity (~1 m m pixels) is sufficient. LHCb is more ambitious While we developers of pixel imagers for science have corners of the pixels, to avoid loss of tracking efficiency. t h e I nt e r n at io n a l L i n e a r C ol l id e r (IL C). I n 2008 K o n s t a nt i n for its stage-two upgrade, as already mentioned. There are not kept up with the evolution of stacked devices, several The St r a sb ou rg g roup le d b y M a rc W i nter h a s a long a nd St e f a n o v o f t h e O p e n Un i v e r s it y s u g g e s t e d t h at M A P S c h i p s several experiments in which such detectors have poten- academic groups have over the past 15 years taken brave d i s t i n g u i s h e d r e c ord o f M A P S d e v e lo p m e nt. A s w e l l a s h i g h l y c o u ld pr o v id e a n o v e r a l l t r a c k i n g s y s t e m o f a b o ut 30 Gpix- tial for particle identification, notably π/K separation by initiatives in this direction, most impressively a Fermi- appreciated telescopes in test beams at DESY for general els with performance far beyond the baseline options at time-of-flight up to a momentum limit that depends on lab/BNL collaboration led by Ron Lipton, Ray Yarema and use, the group supplied its M I MOSA-28 d e v ic e s for t h e fi r s t the time, which were silicon microstrips and a gaseous the scale of the tracking system, typically 8 G e V/ c . Grzegorz Deptuch. This work was done before the technical MAPS-based v e r t e x d e t e c t or: a 356 Mpixel two-layer barrel time-projection chamber. This development was shelved Monolithic and hybrid pixel detectors answer many of the requirements could be serviced by a single technology node, Advances in system for the STAR experiment at Brookhaven’s Relativistic due to delays to the ILC, but the dream has become a reality needs for particle tracking systems now and in the future. so they had to work with a variety of pioneering compa- Heavy Ion Collider. Operational for a three-year physics in the MAPS-based t r a c k i n g s y s t e m for t h e A L IC E d e t e c t or But there remain challenges, for example the innermost nies in concert with excellent in-house facilities. Their the density of r u n s t a r t i n g i n 201 4, t h i s d e t e c t or e n h a n c e d t h e c a p a bi l it y at the LHC, which builds on the impressive ALPIDE chip layers at ATLAS and CMS. In order to deliver the required achievements culminated in three working prototypes, two CMOS digital to look into the quark–gluon plasma, the extremely hot d e v e lo p m e nt b y Wa lt e r Sn o e y s a n d h i s c ol l a b or at or s. T h e vertexing capability for efficient, cleanly separated b and for particle tracking and one for X-ray imaging, namely a electronics for m o f m at t e r t h at c h a r a c t e r i s e d t h e bi r t h o f t h e u n i v e r s e. ALICE ITS-2 s ystem, w it h 12.5 Gpixels, sets the record for charm identification, we need pixels of dimensions about beautiful three-tier stack comprising a thick sensor (for have enabled An ingenious MAPS variant developed by the Semi- any pixel system (see p29). This beautiful tracker has oper- 25 × 2 5 μ m , four times below the current goals for HL-LHC. efficient X-ray detection), an analogue tier and a digital Face-to-face designers to conductor Laboratory of the Max Planck Society – the ated smoothly on cosmic rays and is now being installed They should also be thinner, down to say 2 0 μ m , to preserve tier (see “Stacking for physics” figure). wafer bonding pack more Depleted P-channel FET (DEPFET) – is also serving as a i n t he over a l l A LICE detec tor. The g roup is a l ready push- precision for oblique tracks. For the HL-LHC inner layers, one could imagine a stacked is now a and more high-performance v e r t e x d e t e c t or i n t h e B e l le II d e t e c t or ing to upgrade the three central layers using wafer-scale Solutions to these problems, and similar challenges in the chip comprising a thin sensor layer (with excellent noise commercially electronics at SuperKEKB in Japan, part of which is already operating. stitching and curved sensors to significantly reduce the much bigger market of X-ray imaging, are coming into view performance enabled by an on-chip front-end circuit for mature into each pixel I n t h e DE PF E T, t h e s i g n a l c h a r g e d r i f t s t o a “v i r t u a l g at e” material budget. At the 2021 International Workshop on with stacked devices, in which layers of CMOS-processed each pixel), followed by one or more logic layers. Depending technology

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FEATURE PIXEL DETECTORS

Technology nodes TSMC The relatively recent term “technology node” embraces a number of aspects of commercial integrated circuit (IC) production. First and foremost is the feature size, which originally meant the minimum line width that could be produced by photolithography, for example the length of a transistor gate. With the introduction of novel transistor designs (notably the FinFET), this term has been generalised to indicate the functional density of transistors that is achievable. At the start of the silicon-tracker story, in the late 1970s, the feature size was about 3 µm. The current state-of-the-art i s 5 nm, and the downward Moore’s law trend is continuing steadily, although such narrow lines would of course be far beyond the reach of photolithography. There are other aspects of ICs that are included in the description of any technology node. One is whether they support stitching, which means the production of Wafer thin 12 inch silicon wafers fabricated by Taiwan Semiconductor Manufacturing Company. larger chips by step-and-repeat of reticles, enabling the production of single devices as through-silicon vias and direct-bond a large market). However, other features of sizes 10 × 10 cm2 and beyond, in principle interconnects. A third aspect is whether that are desirable and becoming essential up to the wafer scale (which these days is a they can be used for imaging devices, which for our needs (imaging capability, stitching diameter of 200 or 300 mm, evolving soon to implies optimised control of dark current and stacking) are widely available and less 450 mm). Another is whether they support and noise. For particle tracking, the most expensive. For example, Global Foundries, wafer stacking, which is the production of advanced technology nodes are unaffordable which produces 3.5 million wafers per multi-layer sandwiches of thinned devices (the development cost of a single 5 nm ASIC annum, offers these capabilities at their 32 using various interconnect technologies such is typically about $500 million, so it needs and 14 nm nodes. Scintinel™ Stilbene Scintillation Crystals are the gold standard in neutron-gamma Pulse Shape Discrimination. o n t h e t e c h n olo g y n o d e, o n e s h o u ld b e a ble t o fit a l l t h e lo gic c r e at io n s. T h e i nt e r n at io n a l c o m mu n it y o f d e s i g n e r s s e e (building on the functionality of the RD53 chip) in one or fe w b o u n d a r ie s t o t h e i r a r t, b e i n g s u s t a i n e d b y t h e a v a i l- Unlike most neutron detectors, stilbene is two layers of 25 25 μm pi xels. The overall t hic k ness could ability of stitched devices to cover large-area tracking × sensitive only to high-energy fast neutrons. be 20 μm for the imaging layer, and 6 μm per logic layer, s ystems, a nd mov i ng i nto t he t h i rd d imension to create Directly detecting fast neutrons preserves with a bottom layer sufficiently thick (~100 μm) to give t he t h e m o s t a d v a n c e d pi x e l s, w h ic h a r e o bl i g at or y for s o m e timing, neutron energy distribution, and n e c e s s a r y m e c h a n ic a l s t a bi l it y t o t h e r e l at i v e l y l a r g e s t it c h e d e xcit ing physics goals. Enabling Fast Neutron Detection chips. The resulting device would still be thin enough for a Just like the attribute of vision in the natural world, directional information. Scintinel stilbene is high-quality v e r t e x d e t e c t or, a n d t h e t h i n pl a n a r sensor-layer which started as a microscopic light-sensitive s p o t o n t h e superior to liquid and plastic scintillators for pixels including front-end electronics would be amenable surface of a unicellular protozoan, and eventually reached neutron/gamma discrimination. to full depletion up to the 10-year HL-LHC radiat ion dose. one of its many pinnacles in the eye of an eagle, with its T h e r e a r e g r o up s i n Ja p a n (at K E K le d b y Ya s uo A r a i, a n d amazing “stacked” data processing behind the retina, • Superior Pulse Shape Discrimination at RIKEN led by Takaki Hatsui) that have excellent track silicon pixel devices are guaranteed to continue evolving • Lower Gamma false rate records for developing silicon-on-insulator devices for to meet the diverse needs of science and technology. • Lower Threshold for gamma rejection particle tracking and for X-ray detection, respectively. Will they one day be swept away, like photographic The RIKEN group is now believed to be collaborating with film or bubble chambers? This seems unthinkable at • Excellent Neutron Detection Efficiency Sony to develop stacked devices for X-ray i m a g i n g. G i v e n present, but history shows there’s always room for a Sony’s impressive achievements in visible-light i m a g i n g, new idea.  Crystals are available in sizes up to 5 inches this promises to be extremely interesting. There are many and in various format shapes. Stilbene applications (for example at ITER) where radiation-resistant Further reading crystals are easily integrated with PMT and X-ray imaging will be of crucial importance, so this is an C Chu 2010 Modern Semiconductor Devices for SiPM devices. area in which stacked devices may well own the future. Integrated Circuits (Pearson/Prentice Hall). E H M Heijne 2021 Radiat. Meas. 140 106436. Outlook H Kolanoski and N Wermes 2020 Particle Detectors: The story of frontier pixel detectors is a bit like that of Fundamentals and Applications (Ox ford Universit y Press). For more information go to an art form – say cubism. With well-defined beginnings M R iordan and L Hoddeson 1997 Crystal Fire www.inradoptics.com/scintinel 50 years ago, it has blossomed into a vast array of beautiful (WW Norton and Co).

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‘A CERN for climate change’

An exascale computing facility Bruchez Shutterstock/Benoit modelled on the organisation of CERN would enable a step-change in quantifying climate change, argue Tim Palmer and Bjorn Stevens.

In the early 1950s, particle accelerators were national-level activities. It soon

Univ. OxfordUniv. became obvious that to advance the field further demanded machines beyond the capabilities of single countries. CERN marked a phase transition in this respect, enabling physicists to cooperate around the development of one big facility. Cli- Tim Palmer m a t e s c i e n c e s t a n d s t o s i m i l a rl y b e n e fit is the Royal Society from a change in its topology. High-energy approach Out of computational necessity, existing climate models suffer research professor Modern climate models were devel- from a degree of abstraction that decouples clouds from air currents, for example. in climate physics oped in the 1960s, but there weren’t any at the University clear applications or policy objectives at In addition to more physical models, Building momentum of Oxford. that time. Today we need hard numbers we also need a much better quantifi- A number of us have been arguing for such about how the climate is changing, and an cation of model uncertainty. At pres- a facility for more than a decade. The idea ability to seamlessly link these changes ent this is estimated by comparing seems to be catching on, less for the elo- SUPERCON, Inc. MPI to applications – a planetary information solutions across many low-resolution quence of our arguments, more for the system for assessing hazards, planning models, or by perturbing parameters promise of exascale computing. A facility to Superconducting Wire Products food security, aiding global commerce, of a given low-resolution model. The accelerate climate research in developing guiding infrastructural investments, and particle-physics analogy might be that and developed countries alike has emerged Standard and Speciality designs are available to meet your most demanding much more. National centres for climate everyone runs their own low-energy a s a c or e e l e m e nt o f o n e o f 1 2 br i e fi n g d oc- modelling exist in many countries. But accelerators hoping that coordinated uments prepared by the Royal Society in superconductor requirements. we need a centre “on steroids”: a dedi- experiments will provide high-energy advance of the United Nations Climate Bjorn Stevens cated exascale computing facility organ- insights. Concentrating efforts on a few Change Conference, COP26, in November. is the managing ised on a similar basis to CERN that would high-resolution climate models, where T h i s br ie fi n g fl a n k s t h e E u r o p e a n Un io n’s SUPERCON, Inc. has been producing niobium-based superconducting wires and cables for 58 years. director of the We are the original SUPERCON – the world’s first commercial producer of niobium-alloy based wire and allow the necessary leap in realism. uncertainty is encoded through stochas- “Destination Earth” project, which is part Max Planck t i c m a t h e m a t i c s, i s a h i g h- e n e r g y e ffor t. of its Green Deal programme – a €1 bil- Institute for cable for superconducting applications. Quantifying climate It would result in better and more useful l io n e ffor t o v e r 10 y e a r s t h a t e n v i s io n sthe Meteorology. To be computationally manageable, models, and open the door to cooper- development of improved high-resolution Standard SC Wire Types Product Applications existing climate models solve equations ative efforts to systematically explore m o d e l s w it h b e t t e r q u a nt i fie d u n c e r t a i nt y. NbTi Wires Magnetic Resonance Imaging for quantities that are first aggregated the structural stability of the climate If not anchored in a sustainable organisa- over large spatial and temporal scales. system and its implications for future tional concept, however, this risks throw- Nb3Sn —Bronze Nuclear Magnetic Resonance This blurs their relationship to physical climate projections. ing money to the wind. Nb3Sn —Internal Tin High Energy Physics laws, to phenomena we can measure, and Working out climate-science’s version Giving a concrete form to such a facil- CuNi resistive matrix wires SC Magnetic Energy Storage to the impacts of a changing climate on of the Standard Model thus provides the ity still faces internal hurdles, possibly Fine diameter SC Wires Medical Therapeutic Devices infrastructure. Clouds, for example, are intellectual underpinnings for a “CERN similar to those faced by CERN in its early creatures of circulation, particularly for climate change”. One can and should days. For example, there are concerns Aluminum clad wire Superconducting Magnets and Coils vertical air currents. Existing models argue about the exact form such a centre that it will take away funding from exist- Wire-in-Channel Crystal Growth Magnets attempt to infer what these air currents should take, whether it be a single facil- ing centres. We believe, and CERN’s own Innovative composite wires Scientific Projects would be given information about much ity or a federation of campuses, and on experience shows, that the opposite is larger scale 2D motion fields. There is a the relative weight it gives to particular more likely true. A “CERN for climate necessary degree of abstraction, which questions. What is important is that it change” would advance the frontiers of leads to less useful results. We don’t know creates a framework for European cli- the science, freeing researchers to turn “We deliver when you need us!” if air is going up or down an individual mate, computer and computational sci- their attention to new questions, rather mountain, for instance, because we don’t entists to cooperate, also with application than maintaining old models, and pro- have individual mountains in the model, communities, in ways that deliver the vide an engine for European innovation www.SUPERCON-WIRE.com at best mountain ranges. ma x imum benefit for societ y. that extends far beyond climate change.

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Cosmologist and theoretical physicist Licia Verde discusses the current tension between ea rly- a nd l ate-t i me mea su rement s of t he e x pa n sion r ate of t he un iver se.

Did you always want to be F Camallonga today. Local measurements of the a cosmologist? current expansion rate of the universe, One day, around the time I started for example based on supernovae properly reading, somebody gave as standard candles, which do not me a book about the sky, and I found rely heavily on assumptions about it fascinating to think about what’s cosmological models, give values beyond the clouds and beyond where that cluster around 73 km s–1 Mpc–1. the planes and the birds fly. I didn’t Then t here is anot her, indirect route know that you could actually make to measuring what we believe is a liv ing doing t his k ind of t hing. the same quantity but only within a At that age, you don’t know what a model, the lambda-cold-dark-matter cosmologist is, unless you happen (ΛCDM) model, which is looking at to meet one and ask what t hey do. the baby universe via the cosmic You are just fascinated by questions microwave background (CMB). When Photo courtesy of EUROfusion. Website: www.euro-fusion.org like “how does it work?” and “how we look at t he CMB, we don’t measure do you k now?”. recession velocities, but we interpret a parameter within the model as the Was there a point at which you e x pansion rate of t he universe. The Imaging in radiation environments just got easier decided to focus on theory? ΛCDM model is extremely successful, Not really, and I still think I’m but the value of the Hubble constant somewhat in-between, in the sense using this method comes out at With superior capabilities for operating in radiation environments, the MegaRAD cameras provide that I like to interpret data and around 67 km s–1 Mpc–1, and the excellent image quality well beyond dose limitations of conventional cameras, and are well suited am plugged-in to observational discrepancy with local measurements collaborat ions. I t r y to ma ke is now 4σ or more. for radiation hardened imaging applications connections to what the data mean in light of t heor y. You could say t hat I am What are the implications if this a t heoret ical e x perimentalist. I made tension cannot be explained by a point to actually go and serve at a systematic errors or some other telescope a couple of times, but you Shining light Licia Verde is ICREA professor at the Instituto de misunderstanding of the data? wouldn’t want to trust me in handling Ciencias del Cosmos, University of Barcelona. The Hubble constant is t he only all of the nitty-gritty detail, or to cosmological parameter in the move the instrument around. missing something: how do I know I ΛCDM universe t hat can be measured am missing it? It sounds vague, but I both directly locally and from What are your research interests? t hin k t he field of cosmolog y is ready classical cosmological observations I have several different researc h to ask these questions because we are suc h as t he CMB, bar yon acoust ic projects, spanning large-scale swimming in data, drowning in data, oscillations, supernovae and big- MegaRAD3 produce color KiloRAD PTZ radiation MegaRAD10 produce color st r uct ure, dark energ y, inflat ion or soon will be, and the statistical bang nucleosy nt hesis. It’s also easy or monochrome video up to or monochrome video up to resistant camera with and the cosmic microwave er ror bars are shrin k ing. to understand what it is, and the error 3 x 106 rads total dose 1 x 107 rads total dose Pan/Tilt/Zoom bac kg round. But t here is a common bars are becoming small enough that philosophy: I like to ask how much This explains your current interest it is really becoming make-or-break In the United States: International: can we learn about the universe in in the Hubble constant. What do you for the ΛCDM model. The Hubble a way that is as robust as possible, define as the Hubble tension? tension made everybody wake up. But For customer service, call 1-800-888-8761 For customer service, call [01] 315-451-9410 where robust means as close as Yes, indeed. When I was a PhD student, before we throw the model out of the To fax an order, use 1-315-451-9421 To fax an order, use [01] 315-451-9421 possible to the truth, even if we knowing the Hubble constant at the w indow, we need somet hing more. Email: [email protected] Email: [email protected] have to accept large er ror bars. In 40–50% level was great. Now, we It is really cosmology, everything we interpret are declaring a crisis in cosmology becoming How much faith do you put in the is always in light of a theory, because there is a discrepancy at the ΛCDM model compared to, say, the make-or- Find out more at thermofisher.com/cidtec and theories are always at some very-few-percent level. The Hubble Standard Model of particle physics? level “spherical cows” – they are tension is certainly one of the most break for the It is a model that has only six approx imat ions. So, imag ine we are intriguing problems in cosmology ΛCDM model parameters, most constrained at

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OPINION INTERVIEW OPINION INTERVIEW

the percent level, which explains someone else’s data and re-do the branch technique, with more results hope was to say that we have this of dark mat ter. But i f we don’t live in most of the observations that we CMB with Planck analysis, it’s very important. to come out. Observations of multiple wonderful model of cosmology that a maximally boring universe, we have of the universe. In the case of images from strong gravitational fits really well and implies t hat we have to be careful about playing this Λ, whic h quant ifies what we call CMB without Planck Is there a way to categorise the very lensing is another promising avenue live in a maximally boring universe. game because the universe could be dark energy, we have many orders large number of models vying to that is very actively pursued, and, Then we could have used that to much, much more interesting than of magnitude between theory and no CMB, with BBN explain the Hubble tension? if we are lucky, gravitational waves eventually make the connection to we assumed. experiment to understand, and Until very recently, there was an with optical counterparts will bring in particle physics, say, by constraining for dark mat ter we are yet to find a PI(k) + CMB lensing indirect interpretation of early versus late another important piece of the puzzle. neutrino masses or the temperature Interview by Matthew Chalmers. candidate particle. Otherwise, it does Cepheids – SNIa direct models. But i f t his is really t he case, connect to fundamental physics and then the tension should show up How do we measure the Hubble has been extremely successful. For in ot her obser v ables, specifically constant from gravitational waves? 20 years we have been riding a wave the matter density and age of It’s a beautiful measurement, as of confirmation of theΛ CDM model, TRGB – SNIa the universe, because it’s a very you can get a distance measurement so we need to ask ourselves: if we are constrained system. Perhaps there without having to build a cosmic going to throw it out, what do is some global solution, so a little distance ladder, which is the case Miras – SNIa we subst it ute it w it h? The first change here and a little in the middle, with the other local measurements masers thing is to take small steps away Tully–Fisher relation and a little there … and everything that build distances via Cepheids, from the model, say by adding one would come toget her. But t hat would supernovae, etc. The recession surface brightness flucts. parameter. For a while, you could be rather unsatisfactory because you velocity of the GW source comes say that maybe there is something SNII can’t point your finger at what t he from the optical counterpart and HII galaxies li ke an effect ive neut rino species problem was. Or maybe it’s something its redshift. The detection of the t hat might fi x it, but a solut ion li ke lensing related very, very local – then it is not a GW170817 event enabled researchers t his doesn’t quite fit t he CMB data question of cosmology, but whether to estimate the Hubble constant to any more. I think the community the value of the Hubble constant we be 70 km s–1 Mpc–1, for example, but may be split 50/50 between being measure here is not a global value. I the uncertainties using this novel late-time averages almost ready to throw the model don’t know how to choose between method are still very large, in the out and keeping working with it, GW related these possibilities, but the way the region of 10%. A particular source because we have nothing better observations are going makes me of uncertainty comes from the to use. wonder if I should start thinking in orientation of the gravitational-wave 65 70 75 80 that direction. I am trying to be as source with respect to Earth, but H [km s–1 Mpc–1] Could it be that general relativity 0 model agnostic as possible. Firstly, this will come down as the number (GR) needs to be modified? Hubble trouble Values of the Hubble constant from direct and there are many other people that are of events increases. So this route Perhaps, but where do we modify indirect measurements by different missions, with the grey and pink thinking in terms of models and prov ides a completely different it? People have tried to tweak GR at bands showing the 68% confidence-level values from SH0ES and they are doing a wonderful job. window on the Hubble tension. early times, but it messes around Planck, respectively. Source: arXiv:2103.01183 (accepted by CQG). Secondly, I don’t want to be biased. Gravitational waves have been with the observations and creates a Instead I am trying to see if I can dubbed, rather poetically, “standard bigger problem than we already have. What about possible sources of think one-step removed, which is sirens”. When these determinations So, let’s say we modify in middle experimental error? very difficult, from a particular model of the Hubble constant become times – we still need it to describe Systematics are always unknowns or parameterisation. competitive with existing the shape of the expansion history that may be there, but the level measurements really depends on of the universe, which is close to of sophistication of the analyses What are the prospects for more how many events are out there. ΛCDM. Or we could modify it locally. suggests that if there was something precise measurements? Upgrades to LIGO, VIRGO, plus next- We’ve tested GR at the solar-system major then it would have come up. For t he CMB, we have t he CMB-S4 generation gravitational-wave scale, and the accuracy of GPS is a People do a lot of internal consistency proposal and the Simons Array. observatories will help in this v iv id illust rat ion of its effect iveness checks; therefore, it is becoming These experiments won’t make a regard, but what if the measurements at a planetary scale. So, we’d need increasingly unlikely that it is only huge difference to t he precision of end up clustering between or to modify it very close to where we due to dumb systematics. The big the primary temperature-fluctuation beyond the late- and early-time are, and I don’t know if there are change over the past two years or measurements, but will be useful measurements? Then we really have modificat ions on t he market t hat so is that you typically now have to disentangle possible solutions to scratch our heads! pass all of the observational tests. different data sets t hat g ive you t he that have been proposed because It could also be that the cosmological same answer. It doesn’t mean that they will focus on the polarisation How can results from particle constant changes value as the both can’t be wrong, but it becomes of t he CMB photons. A s for t he local physics help? universe evolves, in which case the increasingly unlikely. For a while measurements, the Dark Energy Principally, if we learn something form of the expansion history would people were saying maybe there is a Spectroscopic Instrument, which about dark matter it could force us to If we are lucky, not be the one of ΛCDM. There is problem w it h t he CMB data, but now started observations in May, will reconsider our ent ire w ay to fit t he some wiggle room here, but changing we have removed those data out of gravitational measure baryon acoustic oscillations observations, perhaps in a way that Λ within the error bars is not the equation completely and there waves with at the level of galaxies to further we haven’t thought of because dark enough to fi x t he mismatc h. are different lines of ev idence t hat optical nail down the expansion history of matter may be hot rather than cold, Basically, t here is suc h a good give a local value hovering around counterparts the low-redshift universe. However, or something else that interacts in –1 –1 agreement between the ΛCDM model 73 km s Mpc , although it’s true will bring it will not help at the level of local completely different w ays. Neut rinos and the observations that you can that the truly independent ones are measurements, which are being are another possibility. There are in another only tinker so much. We’ve tried to in the range 70–73 km s–1 Mpc–1. A lot pursued instead by the SH0ES models where neutrinos don’t behave put “epicycles” everywhere we could, of the data for local measurements important collaboration. There is also another like the Standard Model yet still and so far we haven’t found anything have been made public, and although piece of programme in Chicago focusing on fit t he CMB obser v at ions. Before t hat act ually fi xes it. it’s not a very glamorous job to take the puzzle the so-called tip of the red-giant- the Hubble tension came along, the

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Thanks to a transformative agreement between CERN and 50+ journals including: IOP Publishing, you can: • Publish open access in more than 50 IOP Publishing journals A relational take on quantum mechanics at no cost to you Unknown physics background. Relational quantum Helgoland • Increase your paper’s visibility and impact* mechanics claims to be compatible with • Comply with any open access mandate and policy, even when By Carlo Rovelli several of Bohr’s ideas. In some ways it Allen Lane goes back to the original ideas of Heisen- publishing in non-SCOAP3 journals berg by formulating the theory without a It is often said that “nobody understands reference to a wavefunction. The prop- • Be covered whether your affiliation is primary or secondary quantum mechanics” – a phrase usually erties of a system are defined only when Include articles from CERN experimental collaborations attributed to Richard Feynman. This the system interacts with another system. • statement may, however, be misleading There is no distinction between observer such as ATLAS, CMS, LHCb and ALICE to the uninitiated. There is certainly a and observed system. Rovelli meticulously high level of understanding of quantum embeds these ideas in a more general his- mechanics. The point, moreover, is that torical and philosophical context, which there is more than one way to understand author’s main target is to discuss his own Heisenberg’s he presents in a captivating manner. He Find out more at http://bit.ly/CERNIOP the theory, and each of these ways requires brainchild: relational quantum mechan- vacation even speculates whether this way of think- us to make some disturbing concessions. ics. This approach, however, does not do A bird’s-eye view ing can help us understand topics that, Carlo Rovelli’s Helgoland is therefore a justice to popular ideas among experts, of Helgoland in his opinion, are unrelated to quantum welcome popular book – a well-written such as the many-worlds interpretation. from around the mechanics, such as consciousness. and easy-to-follow exploration of quan- The reader may be surprised not to find turn of the Helgoland’s potential audience is very tum mechanics and its interpretation. anything about the Copenhagen (or, more previous century. diverse and manages to transcend the Rovelli is a theorist working mainly on appropriately, Bohr’s) interpretation. This fact that it is written for the general pub- quantum gravity and foundational aspects is for very good reason, however, since it is lic. Professionals from both the sciences of physics. He is also a very successful pop- not generally considered to be a coherent and the humanities will certainly learn ular author, distinguished by his erudition interpretation. Having mostly historical something, especially if they are not and his ability to illuminate the bigger significance, it has served as inspiration to acquainted with the nuances of the picture. His latest book is no exception. approaches that keep the spirit of Bohr’s interpretations of modern physics. The Helgoland is a barren German island ideas, like consistent histories (not men- book, however, as is explicitly stated by of the North Sea where Heisenberg tioned in the book at all), or Rovelli’s rela- Lane Allen Rovelli, takes a partisan stance, aiming to co-invented quantum mechanics in tional quantum mechanics. promote relational quantum mechanics. 1925 while on vacation. The extraordi- Relational quantum mechanics was As such, it may give a somewhat skewed nary sequence of events between 1925 introduced by Rovelli in an original techni- view of the topic. In that respect, it would and 1926, when Heisenberg, Jordan, Born, cal article in 1996 (Int. J. Theor. Phys. 35 1637). be a good idea to read it alongside books Pauli, Dirac and Schrödinger formulated Helgoland pr e s e nt s a s i m pl i fie d v e r s io n o f with different perspectives, such as Sean quantum mechanics, is the topic of the these ideas, explained in more detail in Carroll’s Something Deeply Hidden (2019) opening chapter of the book. Rovelli’s article, and in a way suitable for a and Adam Becker’s What is Real? (2018). Rovelli only devotes a short chapter to more general audience. The original arti- discuss interpretations in general. This cle, however, can serve as very nice com- Nikolaos Rompotis University is certainly understandable, since the plementary reading for those with some of Liverpool. Oxford University Press University Oxford Particle Detectors – have written a comprehensive textbook by being more up-to-date and compre- Fundamentals and Applications on particle detectors. The authors use hensive. It is more detailed than Particle their broad experience in collider and Detectors by Claus Grupen and Boris By Hermann Kolanoski and underground particle-physics experi- Shwartz – another excellent and recently Norbert Wermes ments, astroparticle physics experiments published textbook with a similar scope – Oxford University Press and medical-imaging applications to and will probably attract a slightly more c o n fid e nt l y c o v e r t h e s p e c t r u m o f expr- advanced population of physics students Throughout the history of nuclear, par- imental methods in impressive detail. and researchers. This new text promises SCAN ME TO FIND OUT MORE ticle and astroparticle physics, novel Particle Detectors – Fundamentals and to become a particle-physics analogue detector concepts have paved the way Applications combines in a single volume of the legendary experimental-nuclear- to new insights and new particles, and the syllabus also found in two well-known physics textbook Radiation Detection and will continue to do so in the future. To textbooks covering slightly different Measurement by Glenn Knoll. * H Piwowar, J Priem, L V arivière, J P Alperin, L Matthias, B Norlander, A Farley, J West, S Haustein (2018) help train the next generation of inno- aspects of detectors: Techniques for Nuclear The book begins with a comprehensive The state of OA: a large-scale analysis of the prevalence and impact of Open Access articles. vators, noted experimental particle and Particle Physics Experiments by W R warm-up chapter on the interaction of PeerJ 6:e4375 https://doi.org/10.7717/peerj.4375 physicists Hermann Kolanoski (Hum- Leo and Detectors for Particle Radiation by charged particles and photons with mat- boldt University Berlin and DESY) and Konrad Kleinknecht. Kolanoski and ter, going well beyond a typical textbook s Norbert Wermes (University of Bonn) Wermes’ book supersedes them both level. This is followed by a very interest-

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OPINION REVIEWS

ing discussion of the transport of charge rays, neutrinos and exotic matter. Final A reference ples, plots and illustrations of excellent carriers in media in magnetic and electric chapters on electronics readout, triggering for lectures on quality. Kolanoski and Wermes have fields, and – a welcome novelty – signal and data acquisition complete the picture. experimental undoubtedly written a gem of a book, formation, using the method of “weight- Particle Detectors – Fundamentals and with value for any experimental parti- methods ing fields”. The main body of the book Applications is best considered a refer- cle physicist, be they a master’s student, is devoted first to gaseous, semiconduc- ence for lectures on experimental meth- in particle PhD student or accomplished researcher tor, Cherenkov and transition-radiation ods in particle and nuclear physics for and nuclear looking for detector details outside of detectors, and then to detector systems postgraduate-level students. The book is physics their expertise. for tracking, particle identification and easy to read, and conceptual discussions calorimetry, and the detection of cosmic are well supported by numerous exam- Peter Krizan University of Ljubljana. Jigal Editions Jigal Le Neutrino de Majorana tum mechanics. With factual moments comically playing with subtleties most and original letters, he focuses on Majo- Cernois would recognise, from cultural By Nils Barrellon rana’s personal and scholarly life, while differences between the two border- Jigal Editions putting a spotlight on the ragazzi di via ing countries to clichés about particle Panisperna and other European physicists physicists, via passably detailed pro- Naples, 1938. Ettore Majorana, one of the who had to face the Second World War. In cedures of access to the experimental physics geniuses of the 20th century, dis- parallel, a present-day neutrino physi- facilities – a clear proof of the author appears mysteriously and never comes cist is found killed right at the border (who is also a physics school teacher) back. A tragedy, and a mystery that has of France and Switzerland. Majorana’s having been on-site. The novel feels captivated many writers. volumetti (his unpublished research notes) like a tailor-made detective story for the The latest oeuvre, Nils Barrellon’s Le become the leitmotif unifying the two entertainment of physicists and physics Neutrino de Majorana, is a French-language stories. Barrellon compares the two eras enthusiasts alike. detective novel situated somewhere at the of research by entangling the storylines And, at the end of the day, what expla- intersection of physics history and sci- to reach a dramatic climax. nation for Majorana’s disappearance ence outreach. Beginning with Majora- Using the crime hook as the predom- could be more soothing than a love story? na’s birth in 1906, Barrellon highlights the inant storyline, the author keeps the lay events that shaped and established quan- reader on the edge of their seat, while Cristina Agrigoroae CERN.

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2021 IEEE NSS MIC 28th International Symposium on Room-Temperature Semiconductor Detectors From CERN to the environment

A recent CERN Alumni Network Technology Daphne event highlighted how skills developed in high-energy physics can be transferred to careers in the environmental industry, writes Craig Edwards.

CERN technologies and personnel make it a hub for so much more than exploring the funda- mental laws of the universe. In an event organ- ised by the CERN Alumni Relations team on 30 A pr i l, five CERN alumni who now work in the environmental industry discussed how their high-energy physics training helped them get to where they are today. One panellist, Zofia Rudjor, used to work on the ATLAS trigger system and the measurement Mario’s mission Panellist Mario Michan’s (left) company, Daphne Technology, aims to minimise air of the Higgs-boson decays to tau leptons. Having and sea pollution for the maritime industry. spent 10 years at CERN, and with the discovery of the Higgs still fresh in the memory, she now I would say CERN is Leaving the field works as a data scientist for the Norwegian Insti- The decision to leave the familiar surroundings Online Conference tute for Water Research (NIVA). “For my current the ‘Champions League’ of high-energy physics requires perseverance, role, a lot of the skills that I acquired at CERN, stressed Rudjor, stating that it is important to from solving complex problems to working with of technolog y! pick up the phone to find out what type of posi- 16 - 23 October 2021 real-time data streams, turned out to be very tion is really being offered. Other panellists also key and useful,” she said at the virtual April noted that it is vital to spend some time to look at event. Similar sentiments were shared by fellow what skills you can bring for a specific posting. panellist Manel Sanmarti, a former cryogenic (a company focused on enabling industries “I think there are many workplaces that don’t engineer who is now the co-founder of Bamboo to decarbonise), and a former investigator of really know how to recruit people with our skills Energy Platform: “CERN is kind of the backbone antihydrogen at CERN’s Antiproton Decelerator, - they would like the people, but they typically of my career – it’s really excellent. I would say also stressed the importance of being familiar don’t open positions because they don’t know it’s the ‘Champions League’ of technology!” with how the sector works, pointing out the exactly how to specify the job,” said Rudjor. However, much learning and preparation is role that policymakers take: “Everything that The CERN Alumni Network’s “Moving Out also required to transition from particle phys- is happening in the environmental field today of Academia” events provide a rich source of ics to the environment. Charlie Cook began his is all because of policymakers,” he remarked. candid advice for those seeking to change direc- career as an engineer at CERN and is now the Another particle physicist who made the tion, while also demonstrating the impact of founder of Rightcharge, a company that helps change is Giorgio Cortiana, who now works at high-energy physics in broader society. The electric car drivers reduce the cost of charging E.ON’s global advanced analytics and artifi- environment-industry event follows oth- and to use cleaner energy sources. Before tak- cial intelligence, leading several data-science ers dedicated to careers in finance, indus- General Chair: Ikuo Kanno ing the plunge into the environmental industry, projects. His scientific background in com- trial engineering, big data, entrepreneurship Deputy General Chair: Ralf Engels he first completed a course at Imperial College plex physics data analysis, statistics, machine and medical technologies. More are in store, Business School on climate-change manage- learning and object-oriented programming is explains head of CERN Alumni Relations, Rachel NSS Co-Chair: Hiroyuki Takahashi ment and finance, which helped him “learn the ideal for extracting meaningful insights from Bray. “One of our goals is to support those in NSS Co-Chair: Craig Woody lingo” in the finance world. A stint at Octo- large datasets, and for coping with everyday their early careers – if and when they decide pus Electric Vehicles was followed by driving a problems that need quick and effective solu- to leave academia for another sector. In addi- MIC Co-Chair: Taiga Yamaya domestic vehicle-to-grid demonstration project tions, he explained, noting the different men- tion to the Moving Out of Academia events, MIC Co-Chair: Jae Sung Lee called Powerloop, which launched at the begin- tality from academia. “At CERN you have the we have recently launched a new series that ning of 2018. “Sometimes it’s too easy to start luxury to really focus on your research, down brings together early-career scientists and RTSD Co-Chair: Ralph James talking in abstract terms about sustainability, to the tiny details – now, I have to be a bit more the companies seeking the talents and skills RTSD Co-Chair: Tadayuki Takahashi but, to really understand things I like to see the pragmatic,” he said. “Here [at E.ON] we are developed at CERN.” numbers behind everything,” he said. instead looking to try and make an impact as Mario Michan, CEO of Daphne Technology soon as we can.” Craig Edwards CERN.

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2021 EPS prizes announced Prize have been named as Uta to Eleni Vryonidou (bottom left) The European Physical Society Bilow (TU Dresden) and Kenneth of the University of Manchester For advertising enquiries, contact CERN Courier recruitment/classified, IOP Publishing, Temple Circus, Temple Way, Bristol BS1 6HG, UK. (EPS) High Energy and Particle Cecire (University of Notre Dame) “for seminal contributions to Georgia Tech Te l +4 4 (0)1 17 930 1 264 E-m a i l s a le s@c e r nc ou r ie r.c om. Physics (HEPP) division has for their contributions to the precision collider phenomenology, Please contact us for information about rates, colour options, publication dates and deadlines. announced the recipients of its International Particle Physics specifically in the development 2021 awards. Torbjörn Sjöstrand Master Classes, and Sascha of the effective field theory (below) (Lund University) and Mehlhase (LMU München) for the approach”, and Benjamin T Sjöstrand creation of the LEGO ATLAS and Nachman (below), who is also other models. The five prizes will a winner of the 2021 EPS Young be presented during the EPS-HEP Experimental Physicist Prize (see Conference on 26 July, which will left), “for precision measurements group at the Center for Relativistic It’s Summertime, take place online. H Liu Max Astrophysics at Georgia Tech, which has made significant contributions Recognition for Ballarino to IceCube by using data to search Amalia Ballarino of CERN has for neutrinos from transient been named the recipient of the sources, including blazar flares. time for holidays and... 2021 IEEE James Wong Award for Bryan Webber (below) (University her significant and continuing Brookhaven hires Gao of Cambridge) have won the contributions to superconductor Experimental nuclear physicist 2021 EPS–HEPP Prize for the materials. In particular, Ballarino Haiyan Gao (below) has been planning your next career step? Join CERN, a unique work environment at conception, development and was recognised for leading appointed associate laboratory realisation of parton-shower successful R&D programmes director for nuclear and particle the cutting edge of technology in a place like nowhere else on earth. Monte Carlo simulations, which with the high-temperature of observables sensitive to jet physics at Brookhaven National

have been key to the experimental superconductor MgB2, including substructure and use of innovative Laboratory (BNL), beginning wire validation of the Standard Model the development of MgB2 machine learning techniques”. 1 June. Gao, whose research CERN currently has diverse student, graduate and and searches for new physics. suitable for cabling, for promoting The award, announced in April interests include the structure of The 2021 Giuseppe and Vanna fruitful cooperation between during the DIS2021 workshop, is the nucleon, searches for exotic Cocconi Prize has been awarded CERN named after the late CERN theorist QCD states and new physics in professional opportunities open for application. to the Borexino Collaboration for Guido Altarelli, who made seminal electroweak interactions, is a its observation of solar neutrinos contributions to QCD. professor at Duke University, and from the pp chain and CNO cycle, has previously held positions at Lund University CMS celebrates theses Argonne and MIT. At BNL she Apply now and take part! The CMS collaboration has replaces Dmitri Denisov, who has recognised Matteo Defranchis held the position on an interim https://careers.cern (University of Hamburg), basis after Berndt Müller’s Cristina Martin Perez (Institut departure last year. Polytechnique de Paris) and research and industry, and Thorben Quast (RWTH Aachen for launching R&D activity in University) with the 2020 CMS

superconductors for future particle Thesis Award. The three theses, Duke University accelerators. The award, which selected from a total of 24 while the 2021 Gribov Medal comes with a $5000 honorarium nominations, focus, respectively, goes to Bernhard Mistlberger and a pure-niobium medal, has on the first experimental (SLAC) for his contributions to been granted annually since 2000, determination of the running multi-loop computations in QCD with CERN being home to more of the top-quark mass, the and to high-precision predictions winners than any other institution. optimisation of algorithms of Higgs- and vector-boson identifying hadronic tau decays in production at hadron colliders. Guido Altarelli Award top-Higgs associated production, Olga Igonkina fellowship The 2021 Young Experimental The 2021 Guido Altarelli Award, and the development of the CMS LHCb researcher Anna Danilina of Physicist Prize has been awarded established in 2016 for outstanding high-granularity calorimeter. Moscow State University has been to Nathan Jurik (CERN) for contributions by junior scientists awarded the 2021 Olga Igonkina outstanding contributions to the to deep-inelastic scattering New ICECUBE spokesperson travel grant for young Russian LHCb experiment, including the (DIS) and related subjects, goes On 1 May, experimental talent in physics. The award, discovery of pentaquarks, and the J R Gaunt astroparticle physicist Ignacio which was established in memory measurements of CP violation and Taboada of the Georgia Institute of the late Russian–Dutch ATLAS mixing in the B- and D-meson of Technology began his two-year physicist Olga “Olya” Igonkina, systems, and to ATLAS physicist term as spokesperson of the who passed away in 2019 at the Ben Nachman (LBNL Berkeley) IceCube collaboration, replacing age of 45, will enable Danilina to for exceptional and innovative Darren Grant who has served as participate in the Rencontres de contributions to the study of QCD spokesperson for the South Pole Blois conference in October, where jets. Last but not least, the three neutrino observatory since 2019. she will present calculations of the winners of the 2021 Outreach Taboada currently leads a research decay of B-mesons to four leptons.

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Career Opportunities

• Quantum Photonics Engineer For our location in Zeuthen we are seeking: Senior Scientist Accelerator Physics – Tenure Track • Systems & Automation Engineer Limited: initially limited to 5 years with the possibility of conversion to a permanent • Delivery Lead position | Starting date: earliest possible | ID: APMA012/2021 | Deadline: 15.07.2021

DESY, with its 2700 employees at its two locations in Hamburg and Zeuthen, is AegiQ is a dynamic company developing one of the world‘s leading research centres. Its research focuses on decoding high-performance photonic systems across the structure and function of matter, from the smallest particles of the universe to the building blocks of life. In this way, DESY contributes to solving the major applications in quantum security, next genera- questions and urgent challenges facing science, society and industry. With its ultramodern research infrastructure, its interdisciplinary research platforms and tion imaging and quantum information its international networks, DESY offers a highly attractive working environment processing. in the fields of science, technologyFeatures and administration as well as for the education of highly qualified young scientists. 10,000h continuous operation Single mode fibre output Recently spun-out from the University of Shef- The photo-injector test facility at DESY in Zeuthen (PITZ, near Berlin) will be expanded to advance the research andIntegrated development cryogenics of tumor therapies with field, AegiQ is backed by Innovate UK and short irradiation durations at high dose19’’ rates rack as or well tabletop as high electron beam leading venture capital funds. We are recruit- JOIN ELI energy (so-called FLASH and VHEE Customradiotherapies). designs These available promise better tumor control with fewer side effects in healthy tissue. The extremely wide ing a cross-disciplinary team to develop our The future is in laser technologies parameter range for electron beams available at PITZ and the high flexibility of product portfolio. the facility allow unique research opportunities for future tailored applications in humans. We are looking for a project leader with strong accelerator experience, who will lead the expansion of the facility for this project and keep an eye on all major influencing factors together with local and international Apply at www.aegiq.com cooperation partners.

About the role: The ELI (Extreme Light Infrastructure) Project is an integral part of the European plan to build • Project management for radiation biology, FLASH and VHEE radiotherapy at the next generation of large research facilities. ELI-Beamlines as a cutting edge laser facility PITZ is currently being constructed near Prague, Czech Republic. ELI delivers ultra-short, • Close collaboration with e.g. dosimetry experts, biologists, physicians • Representation of the project internally and externally ultra-intense laser pulses lasting typically a few tens of femtoseconds with peak power projected • Participation in the research operation of the PITZ accelerator to reach 10 PW. It will make available time synchronized laser beams over a wide range To be successful in this role: Discover what’s out there of intensities for multi-disciplinary applications in physics, medicine, biology, material science etc. • Master‘s degree in physics with PhD or equivalent qualification The high intensities of the laser pulse will be also used for generating secondary sources • Profound and several years of experience in development, technology and operation of accelerator facilities and their applications Take the next step in your career of e- and p+ and high-energy photons. • Experience in beam dynamics Our research groups are expanding and recruiting physicists and engineers. • Experience in project management with Physics World Jobs. • Well-developed skills in interdisciplinary communication and cooperation in international collaborations In our team we therefore have the following positions available: • Business fluent German and English physicsworld.com/jobs • Experience in radiation biology, biophysics, medical technology, especially cancer therapy is advantageous

For further information please contact Dr. Frank Stephan at • Junior Scientist • Senior Engineer • Safety Engineer +49 33762 7-7338 ([email protected]). • Senior Scientist • Vacuum Technician • Optical Engineer Applications (in German or English) should include a detailed curriculum vitae, publication list, explanations and evidence of experience background and 3 • Laser Physicist • Mechanical Designer • X-ray Scientist names for references. • Junior Engineer • Control System Specialist • Opto-mechanics DESY promotes the professional development of women and therefore strongly encourages women to apply for the position to be filled. In addition, severely handicapped persons with equal aptitude are given preferential consideration. The advertised positions are basically suitable for part-time employment.

You can find further information here: www.desy.de/career

Deutsches Elektronen-Synchrotron DESY Human Resources Department | Notkestraße 85 | 22607 Hamburg Phone: +49 40 8998-3392 For more information see our website www.eli-beams.eu and send your application, please.

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Take the next step in your career with Physics World Jobs. physicsworld.com/jobs CERNCOURIER.COM PEOPLE CERNCOURIER OBITUARIES REPORTING ON INTERNATIONAL HIGH-ENERGY PHYSICS Gerd-JürGen Beyer 1940–2021 A pioneer of applied nuclear physics G Beyer Gerd Beyer, who passed away on 20 January aged and, later, head of its radiochemistry group, 81, played a major role in the development of with responsibility for setting up and operating biomedical research, both at CERN’s ISOLDE a new cyclotron. This allowed him to continue facility and at many other laboratories. He will his work on developing new approaches to label- be remembered as a tireless worker in the field ling monoclonal antibodies and peptides with of nuclear and applied nuclear physics combined exotic lanthanide positron emitters produced with new radiochemical methods. at ISOLDE, determining their in vivo stability Gerd was born in Berlin in 1940 and studied and demonstrating their promising imaging radiochemistry at the Technical University of properties. Gerd was also the first to demon- Dresden (TUD). He then joined the Joint Institute strate the promising therapeutic properties of for Nuclear Research (JINR) in Dubna, where the alpha emitter 149 Tb. he developed advanced production methods of When he retired from HUG, Gerd co-proposed rare short-lived radioisotopes for use in nuclear that CERN build a new radiochemical labora- spectroscopy. At the Central Institute for Nuclear tory in connection with ISOLDE. Here, the large Research in Rossendorf, he became proficient knowledge base on target and mass-separator in the use of the U-120 cyclotron and the RFR techniques for the production and handling of research reactor to produce medical radioiso- radionuclides could be used to make samples of topes, and in the development of the associated these high-purity nuclides available for use in a radiopharmaceuticals. He completed his Dr. Gerd Beyer’s work on the production of broader biomedical research programme. Years habil. at TUD on the production of radionuclides radiopharmaceuticals saved innumerable lives. later, Gerd’s initial idea was eventually realised by means of rapid radiochemical methods in with the creation of the CERN-MEDICIS facility. combination with mass separation. Democratic Republic (GDR), based on the Gerd was a first-rate experimental scientist, In 1971 Gerd was invited to ISOLDE, joining Rossendorf positron camera, using gas detectors highly skilled in the laboratory, and he stayed Helge Ravn to prepare extremely pure samples derived from pioneering work at CERN. professionally active to the very end. As a guest of rare long-lived nuclei for studies of their elec- During his visits to CERN, Gerd spotted professor, a member of numerous professional tron-capture decay, in view of their potential the potential of the ISOLDE mass-separation societies and a holder of many consultancy posi- for determining neutrino masses. Back in Ros- technique to allow the introduction and use of tions, he spared no effort in sharing and trans- sendorf, he continued to develop radiopharma- better-suited but hitherto unavailable nuclides. ferring his know-how, recently to the young ceuticals and to introduce them into nuclear In 1985, in close collaboration with ISOLDE, generation of scientists at MEDICIS. medicine in the former East Germany and the he began to prepare for the future use of large During Gerd’s outstanding career, his work on Eastern Bloc countries. He developed a number facilities to produce such radionuclides. He reac- the production of radiopharmaceuticals saved of new methods for labelling and synthesising tivated ISOLDE’s contacts with the University innumerable lives. His R&D towards new radio- radiopharmaceuticals, in particular the rather Hospital of Geneva (HUG), starting a collabo- pharmaceuticals and, in particular, his pioneer- difficult problem of efficiently separating ration on the use of exotic positron-emitting ing work on 149Tb for targeted alpha therapy, is fission-produced99 Mo from large samples of nuclides for PET imaging, which resulted in the o p e n i n g up n e w p e r s p e c t i v e s for e ffic i e nt c an- low-enriched uranium. This brought him into development of new radiopharmaceuticals based cer treatment. It is therefore particularly tragic many collaborations all over the world, with on radionuclides of the rare earths and actinides. t h a t t h e d e v e l o p m e nt o f e ffic i e nt a nt i v i r a l d r u gs a view to transferring his know-how to other Shortly after the fall of the GDR, Gerd lost came too late to support Gerd in his brave fight laboratories. As head of cyclotron radiophar- his job at Rossendorf and had to start a new against COVID-19. maceuticals, he took the initiative to intro- career elsewhere. Via a CERN scientific asso- Gain unique insights on the latest research duce a PET scanner programme in the German ciateship, he became a guest professor at HUG His friends and colleagues. Vladimir KuKulin 1939–2020 breakthroughs and project developments in started his physics studies under the supervision Uzbekistan and Ukraine. He worked as a visit- A brilliant of Arkady Migdal. Vladimir obtained his PhD in ing professor and gave lectures at universities particle physics and related fields 1971 and his DSc in 1991. For more than 55 years, in the Czech Republic, Germany, the UK, Italy, nuclear theorist he worked in the Institute of Nuclear Physics at Belgium, France, the US, Canada, Mexico, Japan Moscow State University (MSU), becoming pro- and Australia, and since 1996 had maintained On 22 December we lost our colleague and fessor of theoretical physics in 1997 and head of a scientific cooperation between MSU and the cerncourier.com friend, a brilliant theoretical nuclear physicist, the laboratory for atomic nucleus theory in 2012. University of Tübingen. Vladimir Kukulin. Vladimir had many close scientific relations, Vladimir’s research interests embraced theo- Vladimir Kukulin was born in Moscow in 1939. including the supervision of students’ work, at retical hadronic, nuclear and atomic physics, He graduated with honours from the Moscow JINR (Dubna), KazNU (Almaty) and other lead- few-body physics, nuclear astrophysics, quan- s Engineering Physics Institute in 1965, where he ing physics institutes in Russia, Kazakhstan, tum scattering theory, mathematical and com-

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PEOPLE OBITUARIES PEOPLE OBITUARIES

putational physics, among others. Many of the O Rubtsova in NN elastic scattering and NN-induced meson Luc PaPe 1939–2021 approaches he developed, such as the multi-clus- production at intermediate energies. ter model of light nuclei, the method of orthog- A combination of strong intuition, compre- onalising pseudopotentials, and the stochastic hensive knowledge, and experience in vari- A remarkable and complete physicist variational method, opened new directions in ous fields of science and technology, enabled nuclear physics and quantum theory of few- and Vladimir to generate new ideas and carry out Our colleague and friend Luc Pape passed away C Pape the hospitality of the ETH Zurich group in CMS, many-body scattering. During the past two dec- pioneering interdisciplinary research at the on 9 April after a brief illness. Luc’s long and to which he brought his expertise on SUSY. ades, Vladimir and his co-workers developed the intersection of physics, mathematics, chem- r i c h c a r e e r c o v e r e d a l l a s p e c t s o f o u r fie l d, f r o m Collaborating closely with many young phys- effective wave-packet continuum discretisation istry and engineering. He made an indispen- the early days of bubble-chamber physics in i c i s t s, h e i nt r o d u c e d i nt o C M S t h e “s t r a n s v e r s e approach for quantum scattering, and proposed sable contribution to solving important applied the 1960s and 1970s, to the analysis of CMS m a s s” m e t h o d for S US Y s e a r c h e s, a n d pio n e e r e d a scheme for the ultra-fast quantum scattering problems, such as controlled thermonuclear data at t he LHC. several leptonic and hadronic SUSY analyses. calculations on a graphics processing unit. fusion, cleaning of natural gas, fire-fighting I n t h e for m e r, L u c c o nt r i b ut e d t o t h e d e v e l o p - He first convened the CMS SUSY/BSM group A deep understanding of nuclear and math- and neutron-capture cancer therapy. m e nt o f s u b t l e m e t h o d s o f t r a c k r e c o n s t r u c t i o n, (2003–2006), then the SUSY physics analysis ematical physics allowed Vladimir to suggest, Vladimir was distinguished by non-standard measurement and event analysis. He partici- g r o up (2007–2008), pr e p a r i n g v a r i o u s t o p ol o g- in 1998, a new mechanism for the short-range thinking, humanity, a sparkling sense of humour pated in important breakthroughs, such as the ic a l s e a r c h e s t o b e p e r for m e d w it h t h e fi r s t L HC nucleon–nucleon (NN) interaction based on the and an inexhaustible love of life. His enthusiasm first evidence for scaling violation in 1978 in collisions. Responsible for SUSY in the Particle formation of the intermediate six-quark bag and intellectual freedom inspired several gen- n e ut r i n o i nt e r a c t i o n s i n BE B C a n d e a rl y s t u d i e s Data Group from 2000–2012, he helped define dressed by meson clouds (the dressed dibaryon). erations of his colleagues and students. We will o f t h e s t r u c t u r e o f t h e w e a k n e ut r a l c u r r e nt. L u c S US Y b e n c h m a r k s c e n a r i o s w it h i n r e a c h o f h a d- He developed, with his colleagues from MSU and always remember Vladimir as an outstanding developed software to allow the identification r o n c ol l i d e r s, pr e s e nt a n d f ut u r e. C o m for t e d b y the University of Tübingen, the original dibaryon scientist, a wise teacher and a good friend. o f pr o d u c e d m u o n s b y l i n k i n g t h e e x t r a p ol a t e d t he d i s c over y of a l ig ht s c a l a r b os on i n 201 2 (a concept for the nuclear force, which received new bubble-chamber tracks to the signals of the necessary feature of but not proof of SUSY), he e x p e r i m e nt a l c o n fi r m a t i o n w it h t h e d i s c o v e r yof Maria Platonova, Olga Rubtsova, e x ter nal BEBC muon ident ifier. continued exploring novel analysis methods hexaquark states at COSY (Jülich) in 2011. More Vladimir Kukulin carried out pioneering research Vladimir Pomerantsev, Igor Obukhovsky Luc’s very strong mathematical background and strategies to interpret any potential evi- recently, Vladimir and his coauthors demon- at the intersection of physics, mathematics, Moscow State University and Heinz Clement was instrumental in these developments. He dence for SUSY par t icles. strated the decisive role of dibaryon resonances chemistry and engineering. Eberhard Karls University of Tübingen. acquired a deep expertise in software and Luc Pape had outstanding competence and rigour. We will remember Luc for the exceptional s t a y e d a t t h e c ut t i n g e d g e o f t h i s fie l d. He a l s o combination of a genuine enthusiasm for Herbert LengeLer 1931–2021 exploited clever techniques and rigorous meth- and produce data-summary (DST) files for the physics, an outstanding competence and rig- o d s t h a t h e a d a p t e d i n f u r t h e r w or k s. A t t h e e n d whole collaboration. Using his strong exper- our in analysis, incorporating quite technical of the bubble-chamber era, Luc was among the t i s e i n m o s t a v a i l a bl e s o f t w a r e t o ol s, L u c pr o - m at ter s, a nd a de e p c onc er n a b out you ng c ol- Leaving a legacy in superconducting cavities e x p e r t s s t u d y i n g t h e c o m p ut i n g e n v i r o n m e nt gressively improved track analysis, quality leagues with whom he interacted beautifully. of future ex periments. He was also one of t he checking and event viewing. DELPHI users Luc had a strong interest in other domains, CERN Experimental physicist Herbert Lengeler, who an SRF cavity with all auxiliaries and a new people involved in the origin of the Physics will remember TANAGRA (track analysis and including cosmology, African ethnicities and made great contributions to the development of helium refrigerator was installed and tested at A nalysis Workstat ion (PAW) tool. g r a p h ic s p a c k a g e), t h e b a c k b o n e o f t h e DE L A N A arts, and Mesopotamian civilisations. With his superconducting radiofrequency (SRF) cavities, CERN’s SPS. In parallel, Herbert orchestrated After this, Luc joined the DELPHI collabo- (DELPHI analysis) program, and DELGRA for w i fe, h e a l s o u n d e r t o o k s o m e q u it e d e m a n d i n g passed away peacefully on 26 January, just three the development of niobium sputtering on cop- ration. A nalysing t he computing needs of t he event visualisation. Himalayan treks. weeks short of his 90th birthday. per cavities as a cheaper alternative to bulk LEP experiments, he was among the first to Luc’s passion for physics never faded. Open We have lost a most remarkable and Herbert was born in 1931 in the German- niobium. Gradually, additional SRF cavities realise the necessity of moving from shared minded, but with a predilection for supersym- complete physicist, a man of great integrity, speaking region of Eastern Belgium. He studied were installed in the LEP collider, resulting in central computing to distributed farms for metry (SUSY), the subtle phenomenology of d e void o f p e r s on a l a m bit ion, a r ic h p e r s on a l- mathematics and engineering at the Université a doubling of its beam energy by the end of its l a r g e e x p e r i m e nt s. He t hu s c o n c e i v e d, p u s h e d w h i c h h e m a s t e r e d br i g ht l y, h e b e c a m e t h e v e r y ity, interested by many aspects of life, and a Catholique de Louvain in Belgium, and exper- running period in 2000. and, with motivated collaborators, built and a c t i v e l e a d e r o f t h e DE L PH I, a n d t h e n o f t h e f u l l very dear friend. imental physics at RWTH Aachen University From 1989 onwards, Herbert gradually retired exploited the DELPHI farm (DELFARM), allow- LEP SUSY groups. in Germany. He worked there as a scientific from the LEP upgrade programme and devoted ing physicists to rapidly analyse DELPHI data A f t e r r e t i r i n g f r o m C E R N i n 2004, h e e nj o y e d His friends and colleagues. assistant and completed his PhD in 1963 on the more time to other activities at CERN, such as construction of a propane bubble chamber, going consultancy for SRF activities at KEK, DESY and Jean Sacton 1934–2021 on to perform experiments with this instrument Jefferson Lab. In 1993 he was appointed project on electron-shower production at the 200 MeV leader for the next-generation neutron source Father of Belgian experimental particle physics electron synchrotron of the University of Bonn. for Europe, the European Spallation Source, a I n 1964 He r b e r t w a s a p p oi nt e d a s a C E R N s t a ff position he held until his retirement from the member in the track chamber and accelera- project and CERN in 1996. Jea n Sac ton, who put Belg ium at t he forefront Sacton was involved including the management of the Belgian tor research divisions. He was involved in the Herbert was always interested in commu- of major discoveries in fundamental physics Interuniversity Laboratory for High Energies. construction, testing and operation of an RF Herbert Lengeler led the SRF upgrade of LEP, nicating his experience to younger people. and the development of associated technolo- in the first direct The foundation in 1972 of the Interuniver- particle separator for a bubble chamber. In 1967 among other key projects. From 1989 to 2001 he frequently gave lectures gies, died peacefully in his home in Brussels sity Institute for High Energies (IIHE) was he then joined a collaboration between CERN on accelerator physics and technology as an on 12 Febr ua r y, age d 86. He combi ne d h i s sc i- observation of charged l a r g e l y d u e t o h i s e ffor t s d u r i n g t h e pr e c e d i n g and IHEP in Serpukhov, in the Soviet Union, the research centre on behalf of CERN. In the honorary professor at the Technical Univer- entific qualities with great human ones, as a decade. Co-directed for many years by its within which he led the construction of an RF following pioneering period up to 1978, he led sity of Darmstadt in Germany. In 1998 he was fir m b o s s b ut a l w a y s pr e s e nt, a t t e nt i v e, w a r m charmed particles in two founders (Sacton for ULB and Jacques particle separator for both IHEP and the French the development of full-niobium SRF cavities awarded an honorary doctorate from the Russian and intentioned. Lemonne for Vrije Universiteit Brussel), IIHE bubble-chamber Mirabelle, which was installed operated at liquid-helium temperatures, with Academy of Sciences for his contribution to the Jean Sacton defended his bachelor’s thesis nuclear emulsions has become the main centre for experimen- in the same institution. all required auxiliary systems. CERN–IHEP collaboration. on mesic atoms in nuclear emulsion at Univer- tal research in particle physics in Belgium, In 1971 the value of SRF separators for The success of the SRF separator led to ambi- Herbert was an enthusiastic musician. He had sité Libre de Bruxelles (ULB) in 1956, contin- and promotes close collaboration with other improved continuous-wave particle beams tious plans for upgrading the energy of LEP been married since 1959 to Rosmarie Müllender- uing there for his PhD. From 1960 to 1965, he microscopes. He defended his thesis in 1961 Belgian institutes. was recognised. This necessitated the use of at CERN, which were initiated in 1981. A first Lengeler, and the couple had four children and surrounded himself with young researchers a nd, t h re e ye a r s l ate r a s a n a s s o c i ate le c t u re r, In the 1970s the IIHE strongly contributed SRF systems with high fields and low RF losses. SRF cavity with its auxiliaries (RF couplers, 10 grandchildren. fo c u s i n g o n t h e pr o p e r t ie s o f h y p e r-f r a g m e nt s became head of the newly created department to t he sc a n n i ng a nd a na lysis of dat a f rom t he Since a development programme for SRF had frequency tuner, cryostat) was installed and produced by the interactions of K mesons in of elementar y par t icle physics. giant bubble chambers GARGAMELLE and just been initiated at the Karlsruhe Institute successfully tested in 1983 in the PETRA collider Enrico Chiaveri CERN; nuclear emulsions, which required significant A t t h e e n d o f t h e 1960 s, S a c t o n b e c a m e pr o - BEBC. In 1973 IIHE staff scanned one of the s of Technology in Germany, Herbert joined at DESY in Hamburg. Following this, in 1987, Herbert’s friends and colleagues. hu m a n r e s o u r c e s t o s c a n t h e e m u l s i o n foi l s w it h fessor and a member of various committees, three events that spectacularly confirmed

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PEOPLE OBITUARIES IIHE the existence of the weak neutral current, for chair from 198 to 1987), the CERN Super Proton which Sacton, together with the other mem- Synchrotron Committee, the CERN Scientific bers of the Gargamelle collaboration, received P ol i c y C o m m it t e e, a n d t h e e x t e n d e d S c i e nt i fic the European Physical Society’s High Energy Council of DESY. While dean of the ULB sciences and Particle Physics Prie in 2009. Other faculty from 1991–1995, he remained active as firsts that Sacton was involved in during director of the laboratory, leaving to his teams the bubble-chamber era included the first the task of analysing DELPHI, H1 and CHORUS direct observation of charged charmed par- data, and preparing the IIHE contribution to ticles in nuclear emulsions, and the meas- the CMS experiment. In 199 he became pres- urement of the violation of scale invariance ident of the particles and fi elds commission of in deep-inelastic scattering. the International Union for Pure and Applied Later, the IIHE, in collaboration with the Physics and a member of the International University of Antwerpen and the University Committee for Future Accelerators, and from of Mons-Hainaut, contributed to the DELPHI 1991–199 chaired the High-Energy Physics experiment at LEP, for which they built the Computer Coordinating Committee. He for- electronics for the muon chambers. The labo- mally retired in 1999. ratory also engaged in the H1 collaboration at Jean Sacton lived a major scientific adven- HERA, DESY. The Belgian contribution to H1 ture starting from the discovery of the first included the construction of two cylindrical mesons to the completion of the Standard multi-wire proportional chambers and associ- Model. Through his quiet strength, profes- ated data acquisition all of the detector’s multi- sionalism, foresight and entrepreneurial wire proportional chambers, during which spirit, he founded, developed and sponsored Sacton continuously ensured that technical this field of research at ULB and made it shine staff were retrained to keep up with the rapid far beyond. pace of change. At the same time, he became a member of the ean Sacton cofounded the nteruniversity aniel Bertrand and Laurent avart European Committee for Future Accelerators (as nstitute for High Energies. Universit libre de ruelles.

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Notes and observations from the high-energy physics community Detectors come to life From the archive: July/August 1981 From hadron therapy to medical imaging, Dreaming large and small techniques from particle physics have had a Over 400 physicists gathered in the relaxed CERN major impact on biological applications. An environment of the Swiss alpine resort arXiv:2105.11949 Australia-based team now proposes to return Villars, 1–7 June, for the European Committee the favour, reporting the first proof-of-concept for Future Accelerators ECFA ‘General simulations of detectors based on biomaterials. Meeting on LEP’, a very high energy The “DNA detector”, writes Ciaran O’Hare of the electron–positron machine. This was in the University of Sydney and co-workers, could be a long tradition of broad consultation across cost-effective, portable and powerful new technology for a low-energy the European HEP community before taking particle tracker for dark matter and other searches. The idea, first major decisions on CERN projects. As Danish proposed in 2012 (arXiv:1206.6809), is to create a “forest” of precisely- physicist Hans Boggild reported: ‘There once LEP Project Leader sequenced single or double-stranded nucleic acids: incoming particles was a place called Villars, where there was Designate Emilio Picasso break a series of strands along a roughly co-linear chain and the more than one star. They talked about LEP reviewing the project severed segments fall to a collection area. Since the sequences of base and the future of HEP, but decisions were status at Villars. pairs in DNA molecules can be precisely amplified and measured, the made in the bar.’ original position of each broken strand can be reconstructed with During recent years, new methods have been perfected which nanometre precision. Particle identification and energy reconstruction enable complex electronic logic to be mass-produced in small might be challenging without a significant scale-up, admits the team, integrated circuits or ‘chips’, whose dimensions are typically but Monte Carlo simulations show excellent potential angular and measured in millimetres. The dramatic rate of progress has provided spatial resolution (≲ 25 degree axial resolution for keV particles and logic units capable of carrying out increasingly complex operations nanometre-scale track segments) that demonstrates the feasibility at higher speed and at lower cost. While the frontier of of t he concept (arX iv:2105.11949). “We hope t hat t his first e x plor at ive programmable intelligence is gradually being extended, physicists study will inspire imminent experimental investigation to resolve can still only dream of the day when they will have fully many of the outstanding issues we have laid out,” they conclude. programmable triggers with on-line event analysis providing digital displays of the physics parameters! Media corner the “coup de théâtre” of the  Based on text on pp240–242 and pp235–236 of CERN Courier Budapest–Marseille–Wuppertal July/August 1981. “This is a unique opportunity to group publishing new theoretical Editor’s note support breakthroughs in nuclear calculations at the same time medicine that we should all be as Fermilab’s “somewhat When LEP was approved for construction 40 years ago, excited about!” barbarically named” Muon g–2 microprocessors were objects of fascination. Reporting on the first ever “Topical Conference on the Application Thomas Cocolios of KU Leuven experiment unveiled its first of Microprocessors to High Energy Physics Experiments” speaking to Medical News Today measurement (7 April). that year, the July/August issue described a great (18 May) about CERN–MEDICIS “Scientists are usually happy when interest among particle physicists in applying and the European medical microelectronics to reject unwanted data. Back then, isotope programme. their theories are confirmed by experiments. This is different with triggering was largely restricted to hardwiring. “What we really need is the Standard Model.” Jump forward to the latest silicon-pixel upgrades to the inner trackers of ‘a disinformation CERN’” TU Dresden particle physicist the LHC experiments, and physicists are able to read out tens of millions of channels at a rate of 40 MHz. Alicia Wanless of the Carnegie Dominik Stöckinger quoted Endowment for International in German news site MDR Peace, speaking in a panel (10 May). discussion about how democracies Total length of the 250 µm can collaborate on disinformation “If you touch a resonating wire, you scintillating fibres in can convince yourself you’re feeling (The Strategist, 18 May). ’ the universe coming into being.” LHCb s new “SciFi tracker”, 11,000 km the first sections of which “Adieu, planète Neptune de Guardian journalist Stuart Jeffries l’infiniment petit…” reviewing Halo, the CERN- were lowered underground Le Monde journalist David inspired artwork by artistic duo in May. Larousserie waxes lyrical on Semiconductor (19 May).

Correction and clarification Margarida Ribeiro’s correct title (CERN Courier May/June 2021 p55) is EIROfor um liaison officer in t he European Commission Directorate-General for Research and Innovation. The concept behind an accelerator-driven critical system (CERN Courier May/June 2021 p11) emerged from several indiv iduals at different inst it utes.

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