CERNJuly/August 2020 cerncourier.com COURIERReporting on international high-energy physics WLCOMEE CERN Courier – digital edition Welcome to the digital edition of the July/August 2020 issue of CERN Courier.

From giant detectors at the receiving end of artificial neutrino beams to vast sub-ice or subsea arrays and smaller setups investigating whether neutrinos are Majorana particles, neutrino experiments span an enormous range of types, scales and locations. Today, as explored in this issue, a new generation of reactor and NEUTRINO accelerator experiments – including DUNE in the US, Hyper-Kamiokande in Japan and JUNO in China – are gearing up to complete the measurements of neutrino- EXPERIMENTS oscillation parameters and establish the neutrino mass ordering. Meanwhile, a series of shorter baseline experiments are scrutinising the three-neutrino paradigm. STEP UP

Coordinated global action has seen Europe, via the CERN neutrino platform, European strategy update unveiled participate in the long-baseline neutrino programmes in Japan and the US. This Neutrons on COVID-19 has proved a major success. The 2020 update of the European strategy for particle Big Science economics physics, released on 19 June, recommends that the neutrino platform receives continued support. Its highest priority recommendations are to pursue an electron–positron Higgs factory to follow the LHC, and that Europe explores the feasibility of a future energy-frontier hadron collider with a Higgs factory as a possible first stage. These are exciting times, and this month’s Viewpoint also calls on particle physicists to highlight the broader socioeconomic impact of our field.

Elsewhere in this issue: a global network of ultra-sensitive magnetometers called GNOME homes in on exotic fields; neutron facilities prepare to study the structure of SARS-CoV-2; graphene-based Hall probes trialled at CERN; reports on the virtual IPAC and LHCP events; CLOUD experiment breaks new ground in atmospheric science; and much more.

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

CCJulAug20_Cover_v3.indd 1 23/06/2020 17:47 CERNCOURIER www. V o l u m e 6 0 N u m b e r 4 J u l y /A u g u s t 2 0 2 0 DIGITIZER CAEN CERNCOURIER.COM FAMILIES Electronic Instrumentation IN THIS ISSUE V o l u m e 60 N u m b e r 4 J u l y /A u g u s t 2 02 0 A new high density and flexible digital solution R5560 - 128 Channel 14-bit @125 MS/s Digitizer R Cubitt J Goodman J Versatile readout system with exceptional performance designed for 3He tubes in neutron detection applications, PMTs, High Purity Germanium Detectors, RPCs, Silicon Strips and others. M Br ice/CER N-PHO T O-201906-179-2 It is equipped with an open FPGA easily customizable by the user with the included programming tool SCI-Compiler, for real-time data processing.

HAWC eye Gamma-ray observations are I spy Neutron diffraction offers unique Hold on tight How fundamental research • 2U, 19” Rackmount unit with automatic fan NEW being pushed above 100 TeV. 12 advantages for studying SARS-CoV-2. 43 drives socioeconomic progress. 47 control • 128 analog input channels, differential input NeWs PeoPle (single ended version coming soon) ANALYSIS ENERGY FRONTIERS FIELD NOTES CAREERS OBITUARIES • 14-bit @125 MS/s ADC Strategy update concludes Quartic coupling probed IPAC goes virtual Surveying the P Lazeyras 1931–2020 T2K publishes CP fit LHCb interrogates LHC physics shines A Michelini 1930–2020 • Maximum flexibility thanks to USB3.0, • • • surveyors • • Top-Higgs interactions X(3872) • Baryon source amid COVID-19 crisis. 21 CERN demands skills • A Minten 1931–2020 Ethernet, and Optical Link interfaces, supporting remote • CLOUD on smog in proton collisions and tools beyond the • A Pullia 1935–2020 management and very fast data flow DT5560SE • Graphene debuts • LEP-era discrepancy scope of normal • T Rodrigo Anoro 32 Channel 14-bit@125 MS/s • Funky physics unravelled. 17 surveyor jobs. 53 1956–2020 • D Tlisov • 2.4” touch screen display for quick configuration and status • 100 TeV photons. 7 1983–2020. 58 control • Easy multiboard synchronization FeAtures Hyper-Kamiokande GNOME NEUTRINOS CP VIOLATION NEUTRON SCIENCE Sensing a passage Tuning in to The search for Neutron sources through the neutrinos leptonic CP violation join the fight NEW unknown A new generation of Boris Kayser unpacks against COVID-19 SCI-Compiler A global network of accelerator and reactor one of the key questions Advanced neutron magnetometers has experiments is opening in neutrino physics. 40 facilities can enable a User Firmware Generator and Compiler for CAEN begun its search for an era of high-precision deeper understanding Programmable Boards exotic fields beyond the neutrino measurements. of SARS-CoV-2. 43 Standard Model. 25 32 • Block diagram based user firmware generator and compiler • Automatic VHDL generation starting from logic blocks and oPINIoN DePArtmeNts virtual instruments VIEWPOINT INTERVIEW REVIEWS FROM THE EDITOR 5 A price worth Lofty thinking Fiction, in theory NEWS DIGEST 15 • Automatic generation of drivers, libraries and demo paying Jasper Kirkby looks at Big Bang • New APPOINTMENTS 54

software for Windows, Linux and macOS to implement Large research how CERN’s CLOUD Perspectives on Matthew Kapust/SURF & AWARDS infrastructures are experiment has Einstein’s E = mc2. 51 communication between devices and PC software RECRUITMENT 55 through USB, ethernet and VME protocol essential drivers of merged the best of On the cover: Preparations economic progress, particle physics and for the DUNE cavern at Sanford BACKGROUND 62 argues Rolf Heuer. 47 atmospheric science. 48 Underground Research CAEN Facility, South Dakota. 32 www.caen.it Small details… Great differences CERN COURIER JULY/AUGUST 2020 3

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HIGH PRECISION POWER SUPPLIES FROM THE HIGH VOLTAGE. EXACTLY. EDITOR

OUT NOW A neutrino success story M Brice/CERN n the 64 years since the direct discovery of the neutrino WITH ONBOARD from a reactor source, experiments with reactor, solar, Iaccelerator, atmospheric, cosmic and geological neutri- nos have taken physicists ever closer to this most ethereal of PYTHON SCRIPTING Standard Model particles. The revelation that neutrinos have mass, confirmed in the 1990s via the discovery of neutrino oscillations, also launched promising theoretical speculations Matthew on the existence of particles beyond the Standard Model. Chalmers Today, as our cover feature explores, a new generation of Editor reactor and accelerator experiments are gearing up to com- plete the measurements of oscillation parameters (p32). A priority is the complex phase of the mixing matrix, which Neutrino platform ProtoDUNE modules in CERN’s EHN1 hall. encodes potential leptonic CP violation (p40) and for which the T2K experiment in Japan recently published hints (p8), while s p e c t r o m e t e r a n d c o nt r i b ut i o n s t o T 2 K’s n e a r- d e t e c t or N D 2 80 another target is the neutrino mass ordering. Three upcoming and its upgrade. ND280, which was built inside the magnet mega-projects – DUNE in the US, Hyper-Kamiokande in Japan from the UA1 experiment in a collaboration with CERN dating a n d J U NO i n C h i n a – h a v e t h e s e e n i g m a s fi r m l y i n t h e i r s i g ht s. from much earlier, is vital for reducing neutrino-interaction Meanwhile, a series of shorter-baseline experiments are to s y s t e m a t ic s, w h i l e t h e N A61 e x p e r i m e nt a t C E R N i s h e l pi n g t o scrutinise the three-neutrino paradigm. improve neutrino-flux predictions. A strong need exists for From giant detectors at the receiving end of artificial further such experiments if maximal physics is to be extracted neutrino beams to vast sub-ice or subsea arrays and smaller from DUNE and Hyper-Kamiokande. setups investigating whether neutrinos are Majorana parti- The recent go-ahead for Hyper-Kamiokande in Japan, along cles, neutrino experiments span an enormous range of types, with the continuing uncertainty over the International Linear scales and locations. Their latest results will be showcased at Collider sited there, have slightly obscured the neat global Ne ut r i n o2020, w h i c h w a s g e t t i n g u n d e r w a y i n a f u l l y v i r t u a l vision of particle physicists back in 2013 of a world with an It would be format as the Courier went to press. intensity frontier in the US, a precision frontier in Japan, and a n e n e r g y f r o nt i e r i n E u r o p e. B ut it w o u l d b e d i ffic u l t t o d e s i gn difficult to NEW Coordinated action two long-baseline accelerator-neutrino experiments more design two Following the recommendations of the 2013 update of the d i ffe r e nt t h a n Hy p e r-K a m io k a n d e a n d DU N E , a n d t h a t br ings long-baseline European strategy for particle physics, Europe chose to par- richer physics opportunities. The 2020 update of the European EDIT your python script directly on browser or locally with accelerator- ticipate in the long-baseline neutrino programmes in Japan strategy for particle physics, which was released just as the access to all hardware parameters neutrino and the US rather than pursue its own facility, instead building Courier went to press (p7), envisions Europe retaining its lead- experiments reciprocal support for the HL-LHC. This coordinated action, via ership at the energy frontier and identifies an electron–positron the CERN neutrino platform, has proved a major success. It has Higgs factory as the highest priority next collider, whether more different UPLOAD and start the script directly on iCS capable device provided a large-scale demonstration of DUNE’s kiloton-scale in Europe or Asia. Appropriately, it recommends that Europe, than Hyper- liquid-argon time-projection chambers and the refurbishment and CERN through the neutrino platform, should continue to CREATE your own visualisation easily in HTML / Javascript / CSS Kamiokande of ICARUS for use in the Fermilab short-baseline programme, support neutrino projects in Japan and the US for the benefit and DUNE and has seen the development of the BabyMIND magnetic of the worldwide neutrino community.

THOUSANDS OF APPLICATIONS POSSIBLE Reporting on international high-energy physics Data logging, event driven voltage channel control, testing, external control of voltage (by temperature changes), block rampup. CERN Courier is distributed Editor Laboratory correspondents INFN Antonella Varaschin UK STFC Jane Binks Technical illustrator General distribution Start easily with the iseg datalogger example, which stores measured values directly on USB flash drive. to governments, institutes Matthew Chalmers Argonne National Jefferson Laboratory SLAC National Accelerator Alison Tovey Courrier Adressage, CERN, and laboratories affiliated Associate editor Laboratory Tom LeCompte Kandice Carter Laboratory Melinda Baker Advertising sales 1211 G e ne v a 23, S w it z erl a nd; Download the latest version from: www.iseg-hv.com/ics with CERN, and to Mark Rayner Brookhaven National JINR Dubna B Starchenko SNOLAB Samantha Kuula Tom Houlden e-mail courrier- individual subscribers. Archive contributor Laboratory Achim Franz KEK National Laboratory TRIUMF Laboratory Recruitment sales adressage@cern.ch It is published six times Peggie Rimmer Cornell University Hajime Hikino Marcello Pavan Chris Thomas runs on: MMS / Mpod multichannel Low and High Voltage per year. The views Astrowatch contributor D G Cassel Lawrence Berkeley Advertisement Published by CER N, 1211 supplies with CC24 Controller card expressed are not Merlin Kole DESY Laboratory Laboratory Spencer Klein Produced for CERN by production Katie Graham Geneva 23, Switzerland SHR labratory High Voltage necessarily those of the E-mail Till Mundzeck Los Alamos National Lab IOP Publishing Ltd Marketing and Tel +41 (0) 22 767 61 11 iCSmini2 Source-Measure-Unit CERN management. [email protected] Enrico Fermi Centre Rajan Gupta Temple Circus, Temple circulation Laura Gillham controller box Guido Piragino NCSL Ken Kingery Way, Bristol BS1 6HG, UK Printed by Warners Advisory board Fermilab Kurt Nikhef Robert Fleischer Tel +4 4 (0)117 929 7481 Advertising (Midlands) plc, Bourne, Peter Jenni Riesselmann Novosibirsk Institute Tel +44 (0)117 930 1026 Lincolnshire, UK Christine Sutton Forschungszentrum S Eidelman Head of Media Jo Allen (for UK/Europe display Claude Amsler Jülich Markus Buescher Orsay Laboratory Head of Media advertising) or © 2020 CER N Philippe Bloch GSI Darmstadt I Peter Anne-Marie Lutz Business Development +44 (0)117 930 1164 (for ISSN 0304-288X Roger Forty IHEP, Beijing Lijun Guo PSI Laboratory P-R Kettle Ed Jost recruitment advertising); Mike Lamont IHEP, Serpukhov Saclay Laboratory Production editor e-mail sales@ Joachim Kopp Yu Ryabov Elisabeth Locci Ruth Leopold cerncourier.com

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Policy European strategy update released FCC/CERN The discovery of the Higgs boson by the ATLAS and CMS collaborations at the LHC in 2012 marked a turning point in particle physics. Not only was it the last of the Standard Model particles to be found, but it is completely different to any particle seen before: a fundamental scalar, with profound connections to the structure of the vacuum. Extensive measurements so far suggest that the particle is the sim­ plest possible version that nature per­ mits. But the study of the Higgs boson is still in its infancy and its properties present enigmas, including why it is so light, which the Standard Model cannot explain. Particle physics is entering a new era of exploration to address these and other outstanding questions, including unknowns in the universe at large, such as the nature of dark matter. Outlining the it s e l f – o ffe r i n g a d e e p e r u n d e r s t a n d i ng CERN and research centres and national The 2020 update of the European strat­ future An artist’s of the electroweak phase transition in the institutes in Europe should be strength­ egy for particle physics (ESPPU), which impression of a early universe, after which the vacuum ened and expanded, in addition to building was released on 19 June during the 199th particle collision gained a non-zero expectation value and strong collaborations with the astropar­ session of the CERN Council, sets out an taking place at a particles were able to acquire mass. ticle and nuclear physics communities. a m bit io u s pro g r a m m e t o c a r r y t h e fie ld future circular “We have started to concretely shape deep into the 21st century. Following two collider, which CERN’s future after the LHC, which is Exploring the next frontier years of discussion and consultation with is one of the a difficult task because of the different The 2013 ESPPU recommended that particle physicists in Europe and beyond, highest priority paths available,” said Ursula Bassler, options for CERN’s next machine after the ESPPU has identified an electron– recommendations president of the CERN Council. the LHC be explored. Today, there are positron Higgs factory as the highest of the ESPPU. The strategy update is the second four possible options for a Higgs fac­ priority collider after the LHC. The ultra­ since the process was launched in 2005, tory in different regions of the world: clean collision environment of such a serving as a guideline to CERN and ena­ an International Linear Collider (ILC) in machine (which could start operation bling a coherent science policy in Europe. Japan, a Compact Linear Collider (CLIC) at at CERN within a timescale of less than Building on the previous strategy update CERN, a Future Circular Collider (FCC­ee) 10 years after the full exploitation of the in 2013, the 2020 update states that the at CERN and a Circular Electron Positron high­luminosity LHC in the late 2030s) successful completion of the high­ Collider in China. As Higgs factories, the will enable dramatic progress in map­ luminosity LHC should remain the E SPP U fi n d s a l l fo u r t o h a v e c o m p a r able ping the diverse interactions between focal point of European particle phys­ re a c h, a l b e it w it h d i ffe re nt t i m e s c he d­ the Higgs boson and other particles, and ics, together with continued innovation u l e s a n d w it h d i ffe r i n g p o t e nt i a l s for t he form an essential part of a research pro­ in experimental techniques. Europe, via study of physics topics at other ener­ gramme that includes exploration of the the CERN neutrino platform, should also gies. While not specifying which facility flavour puzzle and t he neut rino sector. continue to support the Long Baseline should be built, the ESPPU states that Neutrino Facility in the US and neutrino the large circular tunnel necessary for Unprecedented scales projects in Japan. Diverse projects that a future hadron collider at CERN would To prepare for the longer term, the ESPPU are complementary to collider experi­ also provide the infrastructure needed for prioritises that Europe, together with its ments are an essential pillar of the ESPPU FC C- e e a s a p o s s i bl e fi r s t s t e p. I n a d d it i on international partners, explore the tech­ recommendations, which urge European to serving as a Higgs factory, FCC­ee is n ic a l a n d fi n a n c i a l fe a s i bi l it y o f a f ut ure We have laboratories to support experiments ena­ able to provide huge numbers of weak proton–proton collider at CERN with a started to bling, for example, precise investigations vector bosons and their decay products centre­of­mass energy of at least 100 TeV. concretely of flavour physics and electric or mag­ that would enable precision tests of elec­ In addition to allowing searches for new netic dipole moments, and searches for troweak physics and the investigation of phenomena at unprecedented scales, this shape CERN’s axions, dark­sector candidates and feebly t he flavour puzzle. machine would enable the detailed study future after interacting particles. Considering colliders at the energy s of how the Higgs boson interacts with the LHC Cooperative programmes between frontier, a 3 TeV CLIC and a 100 TeV

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circular hadron collider (FCC-hh) were explains Halina Abramowicz, chair of vigorously support theoretical research Cherenkov ring that can be distinguished imal electron–antineutrino enhance- says T2K international co-spokesper-

explored in depth. While the proposed the European Strategy Group, which was covering the full spectrum of particle as being created by an electron or muon. ment (δCP = +π/2), and the 82 and 17 events son Federico Sanchez of the University 3 8 0 G e V CLIC also offers a Higgs factory charged with organising the 2020 update. physics, pursuing new research direc- By changing the polarity of J-PARC’s expected for maximal electron–neutrino of Geneva. “These results indicate that

as a first stage, the dramatic increase “Europe should keep the door open to tions and links with cosmology, astro- magnetic focusing horn, this oscillation enhancement (δCP = –π/2). Being most CP violation in neutrino mixing may in energy possible with a future hadron participate in other headline projects particle physics and nuclear physics. The can be compared to its CP-mirror process. compatible with the latter scenario, be large, and T2K looks forward to con- collider compared to the LHC has led which will serve the field as a whole.” development of software and comput- Since the beam-line and detector com- the T2K data disfavour almost half of tinued operation with the prospect of

the ESPPU to consider this technology ing infrastructures that exploit recent ponents are made out of matter and not the possible values of δCP – including establishing evidence for CP violation in

as the most promising for a future ener- Ramping up accelerator R&D advances in information technology and antimatter, the observation of neutrinos δCP = 0, when averaged over other oscil- neutrino oscillations.” gy-frontier facility. A feasibility study To achieve the ambitious ESPPU goals, data science are also to be pursued in is enhanced compared to antineutrinos. lation parameters – at 3σ confidence. To further improve the experimental

into building such a machine at CERN particle physicists are urged to undertake collaboration with other fields of science The δCP parameter is a cyclic phase: if For the statistically favoured “normal” sensitivity to a potential CP-violating

with FCC-ee as a possible first stage is to vigorous R&D on advanced accelerator and industry, while particle physicists δCP = 0 or ±π, then neutrinos and anti- neutrino-mass ordering, the measured e ffe c t, t h e c ol l a b or a t i o n pl a n s t o u p grade

be established as a global endeavour and technologies, which also drive many should forge stronger relations with the neutrinos change from muon to electron 3σ confidence-level interval forδ CP is the ND280 near detector to reduce system- completed on the timescale of the next other fields of science, industry and European Commission and continue their types in the same way during oscilla- [–3.41, –0.03], while for the “inverted” atic uncertainties and to accumulate more strategy update later this decade. It is also society, notes the report. Europe should leadership in promoting open science. tion; any other value would enhance the mass ordering (in which the first mass Finding data, while J-PARC will increase the beam expected that Europe invests further in develop a technology roadmap, taking “It is an historic day for CERN and for oscillations of either neutrinos or anti- splitting is greater than the second) it is additional intensity by upgrading its accelerator and R&D for the high-field superconducting into account synergies with interna- particle physics in Europe and beyond. neutrinos, violating CP symmetry. Ana- [–2.54, –0.32], with no parameter space sources of beam line. Future neutrino CP violation magnets for FCC-hh while retaining a tional partners and other communities We are all very excited and we are ready lysing data with 1.49 × 1021 and 1.64 × 1021 inside the 1σ bound (see fig ure). CP violation measurements at DUNE and Hyper- programme in the advanced accelerator such as photon and neutron science, to work on the implementation of this protons on target in neutrino- and anti- “Our results show the strongest is one of the Kamiokande are expected to determine technology developed for CLIC, which fusion energy and industry. In addition very ambitious but cautious plan,” said neutrino-beam mode, respectively, T2K constraint yet on the parameter govern- the exact degree of CP violation in the outstanding also has significant potential applica- to high-field magnets, the roadmap CERN Director-General Fabiola Gianotti observed 90 electron–neutrino candi- ing CP violation in neutrino oscillations, neutrino system. tions beyond high-energy physics. should include R&D for plasma-accel- following the unanimous adoption of the dates and 15 electron–antineutrino one of the few parameters governing mysteries The report notes that the timely eration schemes, an international design resolution to update the strategy by the candidates. This may be compared with fundamental particle interactions that in particle Further reading realisation of the ILC in Japan would be study for a muon collider, and R&D on CERN Council’s national representatives. the 56 and 22 events expected for max- has not yet been precisely measured,” physics T2K Collaboration 2020 Nature 580 339. compatible with this strategy and, in energy-recovery linacs. Europe should “We will continue to invest in strong that case, European particle physicists The ESPPU recommendations strongly keep the cooperative programmes between CERN Higgs pHysics would wish to collaborate. “The natural emphasise the need to continue with and other research institutes in CERN’s door open to next step is to explore the feasibility of efforts to minimise the environmen- member states and beyond. These col- First foray into CP symmetry of top-Higgs interactions the highest priority recommendations, tal impact of accelerator facilities and participate in laborations are key to sustained scientific ATLAS and CMS and ATLAS while continuing to pursue a diverse maximise the energy efficiency of future other headline and technological progress, and bring One of the many doors to new physics that ing the kinematic properties of the ttH programme of high-impact projects,” projects. Europe should also continue to projects many societal benefits.” has been opened by the discovery of the process and modifying tH production. Higgs boson concerns the possibility of Exploring the CP properties of these NeutriNos finding charge–parity violation (CPV) in interactions is non-trivial, and requires Higgs–boson interactions. Were CPV to the full capacities of the detectors and Neutrino oscillations constrain leptonic CP violation be observed in the Higgs sector, it would analysis techniques. be an unambiguous indication of physics The collaborations employed In April, the T2K (Tokai to Kamioka) Statistical strike After applying external beyond the Standard Model (SM), and machine-learning algorithms to dis-

collaboration in Japan reported the Nature reactor–neutrino constraints (top), T2K could have important ramifications for entangle the relative fractions of the T2K + reactors (1σ)

strongest hint so far that charge– Source: has achieved the first closed 3σ confidence understanding the baryon asymmetry CP-even and CP-odd components of top- 0.032 T2K only (1σ) parity (CP) symmetry is violated by reactor (1σ) interval on δCP (middle). In the bottom of the universe. Recently, the ATLAS and Higgs interactions. The CMS collaboration the weak interactions of leptons. Based panel, 1σ (box and line) and 3σ (error bar) CMS collaborations reported their first o b s e r v e d t t H pr o d u c t io n a t a s i g n i fic a n c e

on an analysis of nine years of neutrino– 13 0.028 confidence intervals forδ CP are plotted for forays into this area by measuring the of 6.6σ, and excluded a pure CP-odd struc- θ oscillation data, the T2K results exclude 2 the two possible neutrino mass orderings. CP structure of interactions between the ture of the top-Higgs Yukawa coupling at sin a substantial parameter space for δCP, Higgs boson and top quarks. Seeking cess, which accounts for around 1% of the 3.2σ. The ratio of the measured ttH pro- 0.024 the phase thought to govern leptonic CP violation: a complex phase, δCP, in the While CPV is well established in the asymmetry Higgs bosons produced at the LHC, was duction rate to the predicted production violation, at 3σ confidence. While further neutrino mixing matrix (see p40). weak interactions of quarks, and is Higgs-top observed by both collaborations in 2018. rate was found by CMS to be 1.38 with an data are required to confirm the findings, Though models indicate that no value interactions uncertainty of about 25%. ATLAS data also 0.020 explained in the SM by the existence of But the tH production channel is predicted the result strengthens previous observa- of δCP could explain the cosmological a phase in the CKM matrix, the amount of recorded by the to be about six times rarer. This is due to show agreement with the SM. Assuming 0.65 1 (68.27% confidence) tions and offers hope for a future discovery σ matter–antimatter asymmetry without CP V obser ve d i s m a ny order s of m ag n i- ATLAS and CMS destructive interference between higher a CP-even coupling, ATLAS observed ttH of leptonic CP violation at next-genera- 3σ (99.73% confidence) 10 new physics, the observation of leptonic tude too small to account for the observed detectors. order diagrams involving W bosons, and with a significance of 5.2σ. Comparing tion long-baseline neutrino-oscillation 0.60 CP violation would make models such as cosmological matter–antimatter imbal- makes the tH process particularly sensi- the strength of the CP-even and CP-odd experiments due to come online this 8 leptogenesis, which feature heavy Majo- ance. Searching for additional sources tive to new-physics processes. components, the collaboration favours a decade (see p32). 0.55 rana partners for the Standard Model o f C P V i s a m aj or pr o g r a m m e i n p a r t i c l e According to the SM, the Higgs boson CP-mixing angle very close to 0 (indicat-

23 6 Discovered in 1964, CP violation has θ neutrinos, more plausible. physics, with a moderate-significance is “CP even” – that is, it is possible to ing no CPV) and excludes a pure CP-odd –2 ln L 2 0.50

so far only been observed in the weak sin The T2K experiment uses the Super hint among lepton interactions recently rotate-away any CP-odd phase from coupling at 3.9σ. ATLAS did not observe interactions of quarks, mostly recently in 4 Kamiokande detector to observe neu- announced by the T2K collaboration (see the scalar mass term. Previous probes tH production, setting an upper limit on the charm system by the LHCb collabora- 0.45 trinos and antineutrinos generated by story above). It is likely that sources of of the interaction between the Higgs its rate of 12 times the SM expectation. 2 tion. Since the size of the effect in quarks a proton beam at the J-PARC accelera- CP V f rom phenomena b e yond t he scop e and vector bosons by CMS and ATLAS In addition to further probing the CP is too small to explain the observed 0.40 tor facility 2 9 5 k m away. As the beam of the SM are needed, and the detailed support the CP-even nature of the Higgs properties of the top–Higgs interaction matter–antimatter disparity in the uni- travels through Earth, a fraction of properties of the Higgs sector are one of boson, determining its quantum num- with larger data samples, ATLAS and normal order verse, finding additional sources of CP muon neutrinos oscillate into electron several possible hiding places. bers to be most consistent with JPC = 0++, CMS are searching in other Higgs-boson violation is one of the outstanding mys- inverted order neutrinos that are recorded via nuclear- Based on the full LHC Run-2 dataset, though small CP-odd contributions from interact ions for sig ns of CPV. teries in particle physics. The quantum recoil interactions in Super Kamiokande’s ATLAS and CMS studied events where the a more complex coupling structure are mixing of neutrino flavours as neutrinos –3 –2 –1 0 1 2 3 50,000 tonne tank of ultrapure water, Higgs boson is produced in association not excluded. The presence of a CP-odd Further reading travel over large distances provides a way δCP where the charged lepton generated with one or two top quarks before decay- component, together with the dominant ATLAS Collab. 2020 arXiv:2004.04545. s to probe another potential source of CP by the weak interaction creates a ing into two photons. The latter (ttH) pro- CP-even one, would imply CPV, alter- CMS Collab. 2020 arXiv:2003.10866.

8 CERN COURIER JULY/AUGUST 2020 CERN COURIER JULY/AUGUST 2020 9

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Atmospheric science active sensing component made of atom- at CERN during the past year. The firm ing,” says Russenschuck. “Usually the i c a l l y t h i n g r a p h e n e, w h ic h i s e ffe c t i v e l y sought to develop and test the device operation of Hall sensors at cryogenic two-dimensional, a graphene-based ahead of a full product launch by the end temperatures requires careful calibra- CLOUD clarifies cause of urban smog H a l l pr o b e i n pr i n c i pl e s u ffe r s n e g l i g i bl e of this year, and the results so far, based tion and in situ cross-calibration with planar Hall effects and therefore could on well-calibrated field measurements fluxmetric methods. Moreover, we are H Cawley Ur b a n p a r t i c l e p ol lut i o n r a n k s fi f t h i n t he enable higher precision mapping of local in CERN’s reference magnets, have been n o w e x pl or i n g t h e s e n s or s o n a r o t a t i n g risk factors for mortality worldwide, and magnetic fields. ver y prom ising. “The col labor at ion has shaft, which could be a breakthrough for is a growing problem in many built-up Stephan Russenschuck, head of the proved that the sensor has no planar There is extracting local, transversal field har- areas. In a result that could help shape magnetic measurement section at CERN, effect,” says Paragraf’s Ellie Galanis. monics. Graphene sensors could get rid policies for reducing such pollution, the spotted the potential of graphene-based “T h i s w a s a l e a r n i n g s t e p. T h e r e i s pr o b- probably no of the spurious modes that come from CLOUD collaboration at CERN has uncov- Hall probes when he heard about a talk ably no other facility in the world to be other facility nonlinearities and planar effects.” ered a new mechanism that drives winter given by Paragraf – a recent spin-out able to confirm this, so the project has in the world CERN and Paragraf, which has pat- smog episodes in cities. from the department of materials sci- been a big w in on bot h sides.” to be able to ented a scalable process for depositing Winter urban smog episodes occur ence at the University of Cambridge – at T h e g r a p h e n e H a l l s e n s or a l s o o p e r a t e s confirm two-dimensional materials directly onto when new particles form in polluted air a magnetic measurement conference in over a wide temperature range, down to this, so the semiconductor-compatible substrates, trapped below a temperature inversion: December 2018. This led to a collabo- liquid-helium temperatures at which pl a n to re le a s e a joi nt w h ite p ap e r c om- warm air above the inversion inhibits ration, formalised between CERN and superconducting magnets in the LHC project has municating the results so far and detail- convection, causing pollution to build up Paragraf in April, which has seen several operate. “How these sensors behave at been a big win ing the sensor’s performance across a near the ground. However, how additional role in particle formation, simply Clearer view episode with a high number of particles. graphene sensors installed and tested cryogenic temperatures is very interest- on both sides range of magnetic fields. aerosol particles form and grow in this exchanging with ammonium nitrate in Large-eddy “Although the emission of nitrogen highly polluted air has puzzled research- the particles. However, the new CLOUD simulations of oxides is regulated, ammonia emissions Dark m atter Dark reflections KIT ers because they should be rapidly lost study finds that small inhomogenei- urban flow patterns are not and may even be increasing with The FUNK through scavenging by pre-existing ties in the concentrations of ammonia depicting pollution the latest catalytic converters used in Funky physics experimental aerosol particles. CLOUD, which uses an and nitric acid can drive the growth inhomogeneities gasoline and diesel vehicles,” explains area, where the ultraclean cloud chamber situated in a rates of newly formed particles up to superimposed on CLOUD spokesperson Jasper Kirkby. “Our at KIT black-painted floor beamline at CERN’s Proton Synchrotron more than 100 times faster than seen a composite study shows that regulating ammonia can be seen with the to study the formation of aerosol particles before, but only in short spurts that London skyline. emissions from vehicles could contribute Using a large spherical mirror as an photomultiplier and their effect on clouds and climate, have previously escaped detection. to reducing urban smog.” electromagnetic dark-matter antenna, tube–camera pillar has found that ammonia and nitric acid These ultrafast growth rates are suf- z CLOUD’s science is described in depth in a novel experiment at Karlsruhe Insti- at the centre and the can provide the answer. ficient to rapidly transform the newly our interview with Jasper Kirkby on p48. tute of Technology (KIT) called FUNK – mirror on the left. Deriving in cities mainly from vehicle formed particles to larger sizes, where F i n d i n g U(1) s o f a No v e l K i n d – h a s s e t a n emissions, ammonia and nitric acid were they are less prone to being lost through Further reading improved limit on the existence of hidden previously thought to play a passive scavenging, leading to a dense smog CLOUD Collab. 2020 Nature 581 184. photons as candidates for dark mat ter. Despite overwhelming astronomical Paragraf/CERN A pplicAtions e v id e n c e for t h e e x i s t e n c e o f d a r k m a t t e r, Graphene trialled at direct searches for dark-matter particles at colliders and dedicated nuclear-recoil CER N for mag net ic experiments have so far come up empty for the Pierre Auger Observatory with a dish-antenna at the University of Tokyo h a n d e d. W it h t h e s e s e a r c h e s b e i n g m o s t l y surface area of 14 m2 – in the basement and the SHUKET experiment at Paris- measurements sensitive to heavy dark-matter particles, of KIT. Various photodetectors placed at Saclay – though FUNK’s factor-of-10 namely weakly interacting massive par- t h e r a d iu s p oi nt a l l o w F U N K t o s e a r c h for larger mirror surface brings a greater ticles (WIMPs), the search for alternative a signal in different wavelength ranges, e x p e r i m e nt a l s e n s it i v it y, s a y s t h e t e a m. First isolated in 2004 by physicists at the light dark-matter candidates is growing c or r e s p o n d i n g t o d i ffe r e nt h i d d e n-p ho - Other experiments, such as NA64 at CERN University of Manchester using pieces of in momentum. Hidden photons, a cold, ton masses. The dark-matter nature of which employs missing-energy tech- sticky tape and a graphite block, the one- ultralight dark-matter candidate, arise a possible signal can then be verified by niques, are setting stringent bounds on atom-thick carbon allotrope graphene in extensions of the Standard Model that observing small daily and seasonal move- the strength of dark-photon couplings has been touted as a wonder material c o nt a i n a n e w U(1) g a u g e s y m m e t r y a n d ments of the spot around the radius point for masses in t he MeV range and above. on account of its exceptional electrical, are expected to couple very weakly to as Earth moves through the dark-matter “The mass range of viable hidden- thermal and physical properties. Turn- c h a r g e d p a r t i c l e s v i a k i n e t i c m i x i n g w it h fie l d. T h e br o a d b a n d d i s h-a nt e n n a tech- photon dark matter is huge,” says FUNK ing these properties into scalable com- regular photons. Laboratory experiments nique is able to scan hidden photons over collaborator Joerg Jaeckel of Heidelberg mercial devices has proved challenging, that are sensitive to such hidden or dark a large parameter space. Un i v e r s it y. “For t h i s r e a s o n, t e c h n i q u e s however, which makes a recently agreed photons include helioscopes such as the C o m pl e t e d i n 2018, t h e e x p e r i m e nt t o o k that can scan over a large parameter c ol l a b or a t io n b e t w e e n C E R N a n d U K fi r m CAST experiment at CERN, and “light- data during last year in several month- space are especially useful, even if they Paragraf on graphene-based Hall-probe shining-through-a-wall” methods such long runs using low-noise photomulti- cannot explore couplings as small as sensors especially novel. as t he A LPS e x periment at DESY. pl i e r t u b e s. I n t h e m a s s r a n g e 2.5–7 eV, t h e is possible with some other dedicated With particle accelerators requiring 2D sense Paragraf and CERN scientists setting up the graphene Hall sensor for performance evaluation in F U N K e x ploit s a n o v e l “d i s h a nt e n n a” data exclude a hidden-photon coupling methods. A future exploitation of the large numbers of normal and super- the reference dipole magnet of CERN’s magnetic measurement section. m e t h o d fi r s t pr o p o s e d i n 201 2, w h e r e bya stronger than 10–12 i n k i n e t i c m i x i n g. “T h i s setup in other wavelength ranges is conducting magnets, high-precision hidden photon crossing a metallic spheri- is competitive with limits derived from possible, and FUNK therefore carries an and reliable magnetic measurements c u r r e nt pr o p or t io n a l t o t h e fie l d s t r e n g t h non-perpendicular field components in cal mirror surface would cause faint elec- astrophysical results and partially exceeds enormous physics potential.” are essential. While the workhorse for when the sensor is perpendicular to a the three-dimensional sensing region tromagnetic waves to be emitted almost The mass those from other existing direct-detec- these measurements is the rotating-coil magnetic field. However, measurement of existing Hall probes can increase the perpendicularly to the mirror surface, and tion ex periments,” says FUNK principal Further reading range of magnetometer with a resolution limit uncertainties in the 10–4 range required measurement uncertainty, requiring b e fo c u s e d o n t h e r a d iu s p oi nt. T h e e x p e r- invest ig ator Ralph Engel of KIT. A Andrianavalomahefa et al. 2020 of the order of 10–8 Vs, the most impor- for d e t e r m i n i n g fie l d m u l t i p ol e s a r e d if- complex and time-consuming calibra- iment was conceived in 2013 at a workshop viable hidden- So far, two other experiments of this arXiv:2003.13144. tant tool for local field mapping is the ficult to obtain, even with the state-of- tion and processing to separate true sig- at DESY when it was realised that there photon dark type have reported search results for D Horns et al. 2013 J. Cosmol. Astropart. s Hall probe, which passes electrical the-art devices. False signals caused by nals from systematic errors. With an was a perfectly suited mirror – a prototype matter is huge hidden photons in this energy range – the Phys. 1304 016.

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NEWS ANALYSIS

AstrowAtch 100 TeV photons test Lorentz invariance

Over the past decades, the photon collab. HAWC emission from astronomical objects has been measured across 20 orders of magnitude in energy, from radio up to TeV gamma rays. This has not only led to many astronomical discoveries, but also, thanks to the extreme distances and energies involved, allowed researchers to test some of the fundamental tenets of physics. For example, the 2017 joint measurement of gravitational waves and gamma rays from a binary neutron-star merger made it possible to determine the speed of gravity with a precision of less than 10–16 compared to the speed of light. Now, the High-Altitude Water Cheren- kov (HAWC) collaboration has pushed the energy of gamma-ray observations into new territory, placing constraints on Lorentz-invariance violation (LIV) that are up to two orders of magnitude tighter than before. Lett. Rev. Phys. and above) cosmic rays are produced, Models incorporating LIV allow for but could also allow new constraints

modifications to the standard energy– to be placed on LIV. The spectra of four 124

momentum relationship dictated by 021102 sources studied by the collaboration did special relativity, predicting phenom- n o t s h o w a n y s i g n s o f a c ut o ff, a l l o w i n g enological effects such as photon decay HAWC to exclude the LIV energy scale to and photon splitting. Even if the prob- 2.2 × 1031 eV – an improvement of one-to- ability for a photon to decay through two orders of magnitude over previous such effects is small, the large distances limits. involved in astrophysical measurements in principle allow experiments to detect Pushing the limits it. The most striking implication would High altitude lar. But their indirect detection and the It is likely that LIV will be further con- be the existence of a cutoff in the energy Several different large background coming from cosmic strained in the near future, as a range of spectrum above which photons would sources are observed rays make such measurements difficult. new high-energy gamma-ray detectors decay while travelling towards Earth. by the H AWC Recently, significant improvements are developed. Perhaps the most powerful Simply by detecting gamma-ray pho- observatory (top) to have been made in ground-based detec- of these is the Large High Altitude Air tons above the expected cutoff would put emit photons at tor technology and data analysis. The Shower Observatory (LHAASO) located strong constraints on LIV. energies exceeding Japanese–Chinese Tibet air shower in the mountains of the Sichuan prov- 56 TeV. The gamma-ray experiment ASγ, a Cher- ince of China, the first stage of which Expensive and complex bright source enkov-based detector array built at an commenced data-taking in 2018. Once Vacuum solutions Increasing the energy limit for photons on the right of the altitude of 4 km in Yangbajing, added finished, LHAASO will be close to two with which we observe the universe is, lower image underground muon detectors to allow orders of magnitude more sensitive than however, challenging. Since the flux of is the strongest hadronic air showers to be differen- HAWC at 100 TeV and capable of pushing a typical source, such as a neutron star, contributor to the tiated from photon-induced ones via the photon energy into the PeV range. decreases rapidly, ever-larger detectors LIV limit. the difference in muon content, and Additionally, the limit of direct-detection from a single source are needed to probe higher energies. improved data-analysis techniques to measurements will be pushed beyond Photons with energies of hundreds of more accurately remove the isotropic that from Fermi-LAT and DAMPE by the GeV can still be directly detected using all-sky background. In 2019, this ena- Chinese European High Energy cosmic Pfei er Vacuum is proud to have been a supplier of innovative and customized vacuum solutions to the particle accelerator satellite-based detectors equipped bled the ASγ team to observe a source at Radiation Detector (HERD), a 1.8 tonne community for more than 50 years. Our complete product portfolio for vacuum technology, our focus on competent and with tracking and calorimetry. How- e n e r g ie s a b o v e 100 TeV for t h e fi r s t t i m e. calorimeter surrounded by a tracker specialized advice supported by robust and reliable service, makes Pfei er Vacuum the partner of choice for the analytical ever, these instruments, such as the This measurement was soon followed by scheduled for launch in 2025, which is and research communities worldwide. US–European Fermi-LAT detector and m e a s u r e m e nt s o f n i n e d i ffe r e nt s o u r c e s foreseen to be able to directly detect pho- the Chinese–European DAMPE detector, above 56 TeV by the HAWC observatory tons up to 100 TeV. ■ Pumps for vacuum generation down to UHV require a mass of several tonnes, making located at 4 km altitude in the moun- ■ Vacuum measurement and analysis equipment launching them expensive and complex. tains near Puebla, Mexico. These new Further reading ■ Leak detectors and integrity test systems To get to even higher energies, ground- measurements of astrophysical sources, HAWC Collab. 2020 Phys. Rev. Lett. 124 021102. ■ Vacuum chambers and components based detectors, which detect gamma which are likely all pulsars, could not HAWC Collab. 2020 Phys. Rev. Lett. 124 131101. ■ Pumping stations and customized solutions rays through the showers they induce only lead to an answer of the question Tibet ASγ Collab. 2019 Phys. Rev. Lett. in Earth’s atmosphere, are more popu- as to where the highest energy (PeV 123 051101. Are you looking for a perfect vacuum solution? Please contact us: Pfeiffer Vacuum (Schweiz) AG · T +41 44 444 22 55 · F +41 44 444 22 66 · [email protected] 12 CERN COURIER JULY/AUGUST 2020 www.pfeiffer-vacuum.com

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extremes. Scientists in Paris have t ransit ion w as e xcited at 1631 nm t he rig idit y dependences of neon, now detected denizens of this – a w aveleng t h used for opt ical- mag nesium and silicon nuclei third kingdom of particles for fibre telecommunication, thus were found to be bot h ident ical t he first t ime (Science 368 173). affording t he researc hers access and markedly different from The team used the quantum Hall to superior optical devices. Laser helium, carbon and ox ygen effect to build an anyon collider spectroscopy of mesonic atoms cosmic rays above 86.5 GV (Phys. in a 2D electron gas, and observed could place upper limits on exotic Rev. Lett. 124 211102). The new M Brice/CERN-PHOTO-201911-394-28 correlations corresponding to forces, claims the team. A MS data, whic h comprise about “fractional” statistics with a t wo million cosmic rays of eac h phase of π/3. Anyons are the Multimessenger non-coincidences species, suggest a new subdiv ision Mark Bissell (University of Manchester) most recent of a growing list of The ANTARES collaboration, of primar y cosmic rays into at inspects the CRIS setup at CERN. fundamental ideas observed first which operates a neutrino least t wo dist inct classes. as an emergent phenomenon in a telescope 2.5 km under the Radioactive spectroscopy condensed-matter system. Mediterranean Sea, has Quark-matter cores A team at CERN’s ISOLDE reported a search for neutrino A st ropar t icle t heorists have facility has staked a claim to Thoroughly modern Millikan counter par ts to si x g rav itat ional- uncovered ev idence t hat the first laser-spectroscopy A dark sector could be introduced w ave events t hought to orig inate matter in the interior of measurements of a shor t- into the Standard Model via a in the coalescence of binary maximally massive stable lived radioactive molecule, new gauge field, the dark photon, black holes observed by LIGO or neutron stars (NSs) may exist opening new opportunities which can transform back and Virgo bet ween June and Aug ust in t he deconfined phase of

to test physics beyond the forth into ordinary photons. F Montanet quantum chromodynamics. Standard Model (BSM). A Should the dark photon be The team used gravitational Proton Synchrotron Booster massless, dark-sector particles waves from NS mergers and beam collided w it h a uranium- that couple to it should also have electromagnetic observations carbide target to produce small effective electric charges. of binary systems with a pulsar radioactive radium isotopes that In 2017 a protot y pe scint illator– (a highly magnetised rotating RELIABLE for med radioact ive radium- bar array called the milliQan NS) to constrain theoretical monofluoride (RaF) ions in a demonst rator w as installed 33 m models. While 1.4 M  NSs are fluoride-rich gas surrounding from t he interact ion point of t he still expected to have neutron UNDER ALL the target. By using ISOLDE’s CMS experiment at the LHC, to cores, quark–matter cores should collinear resonance ionisation fill a high-mass gap in searches now be considered the standard spectroscopy (CRIS) setup, for such particles. The team has scenario for NSs of around CONDITIONS. the team was able to identify now reported a first search using A visualisation of the ANTARES 2M, say t he aut hors (Nat. Phys. the low-lying energy levels of the prototype. The results match detector. doi:10.1038/s41567-020-0914-9). RaF and demonst rate t hat it the ArgoNeuT collaboration’s Heading into the unknown to open new horizons can be laser cooled for f ut ure leading exclusion of new particles 2017 (Eur. Phys. J. C 80 487). While Milestone for open science demands reliable tools. Help turn your resarch precision studies, as implied with a charge of more than about previous analyses included only Researc hers at CERN can now goals into reality. by theoretical calculations. 0.1e and a mass of a few GeV upward-going muon neutrinos, publish open-access in 42 of t he Vacuum valve solutions and bellows Radioactive molecules promise (arXiv:2005.06518), and the team the new result includes all jour nals of t he publishing ar m high sensitivity to BSM physics is now pursuing an opt imised flavours and the whole sky. of the UK Institute of Physics, from VAT provide unfailing reliability as certain isotopes exhibit detector w it h 100 t imes t he mass. The search for prompt neutrino IOP Publishing, which also and enhanced process safety – deformations such as nuclear emission w it hin ±500 seconds of publishes t his mag a zine. The under all conditions. pear shapes, which should Pionic helium sighted in Villigen the events yielded no candidates. agreement includes authors amplify non-standard effects Researc hers have used an intense Though neutrino counterparts w it h a secondar y affiliat ion to (Nature 581 396). pion beam at the Paul Scherrer are not expected in typical CERN and CERN experimental Inst it ute in Villigen, Sw it zerland, binary-black-hole mergers, collaborations, and the CC-BY Anyon statistics observed and equipment constructed systems with asymmetric or license will allow authors to In 3D space, the many-body at CERN via the ASACUSA very large masses are less well retain copyright. This is the w ave f unct ion accumulates a collaborat ion, to sy nt hesise understood theoretically. 10th arrangement of its kind phase 0 or π when t wo par t icles pionic helium atoms (Nature for IOP Publishing, and t he first are exchanged, the basis of a 581 37). The team at tempted to AMS continues to surprise for CERN, marking a milestone f undamental classificat ion of excite pionic orbital transitions The A lpha Mag net ic Spect rometer tow ards e x tending t he open particles as bosons or fermions. in t he metastable He 2+e–π– atom (A MS) e x periment on t he dissemination of its research. In 1982 Frank Wilczek showed using lasers, w it h t he resonance Inter nat ional Space Stat ion has The ag reement builds on t he that in two dimensions other evidenced by neutron, proton published t he first measurements CERN-hosted SCOAP3 initiative, phases can be realised too, and deuteron fragments from of t he rig idit y (p/q) dependence whic h in 2014 established free defining types of elementary the resulting electromagnetic of t he flu x of heav y species of and immediate open access to excitations that lie somewhere cascade and fission. After several cosmic rays. Follow ing prev ious published articles as the standard between the boson and fermion sur prising null obser v at ions, a unexpected results from AMS, in par t icle physics.

www.vatvalve.com CERN COURIER JULY/AUGUST 2020 15

CCJulAug20_NewsDigest_v2.indd 15 22/06/2020 18:49 CERNCOURIER www. V o l u m e 6 0 N u m b e r 4 J u l y /A u g u s t 2 0 2 0 CERNCOURIER.COM ENERGY Design better FRONTIERS devices — faster. Reports from the Large Hadron Collider experiments Engineers from Fraunhofer IAPT used topology CMS optimization and additive manufacturing to design a heat sink, a common component in many electronic Vector-boson scattering probes quartic coupling devices. The topology-optimized design was then

transformed into a simulation application to automate ± ± The electroweak (EW) sector of the a nd muon s. The W W and WZ produc- –1 and customize certain design tasks. Now, engineers, Standard Model (SM) predicts self- CMS 137 fb (13 TeV) tion modes were studied by simulta- designers, and manufacturers companywide are able interactions between W and Z gauge Vγ data neously measuring their production to efficiently optimize intricate heat sink geometries bosons through triple and quartic 400 wrong sign bkg. unc. cross sections using several kinemat- other bkg. EWK WZ and prepare them for 3D printing. g a u g e c o u pl i n g s. Fol l o w i n g fi r s t m e as- ical observables. The measured total WZ ± ± urements at LEP and at the Tevatron ZZ cross section for W W production of The COMSOL Multiphysics® software is used for during the 1990s, these interactions 300 nonprompt 3.98 ± 0.45 (± 0.37 stat. only) fb is the simulating designs, devices, and processes in all fields are now a core part of the LHC physics tVx most accurate to date, w it h a precision of engineering, manufacturing, and scientific research. programme, as they offer key insights of roughly 10%. No deviation from SM into EW symmetry breaking, which, 200 predictions is evident.

See how you can apply it to topology optimization and events/bin in the case of the SM, causes the W and Though the contribution from additive manufacturing processes. Z bosons to acquire mass as a result of background processes induced by the the Brout–Englert–Higgs mechanism. strong interaction is considerably Topology optimization of a heat sink. 100 comsol.blog/3D-printing-optimization The quartic coupling can be probed larger in the WZ and ZZ final states, at colliders via rare processes such as the scattering centre-of-mass energy tri-boson production, which the CMS and the polarisation of the final-state collaboration observed for the first 1.4 bosons can be measured as these final time earlier this year, and vector-boson states can be more fully reconstructed scattering (VBS). 1.0 than in W±W± pr o d u c t i o n. To o p t i m a l l y The scattering of longitudinally data/SM isolate signal from background, the 0.6 polarised W and Z bosons is a particu- kinematical information of the WZ la rly interest ing probe of t he SM, as its –1.0 –0.5 0 0.5 1.0 and ZZ candidate events is exploited tree-level amplitudes would violate BDT score with a boosted decision tree and u n it a r it y at h ig h e ne rg ie s w it hout de l- matrix element likelihood techniques, icate cancellations from quartic gauge respectively (see figure). The observed –1 couplings and Higgs-boson contribu- CMS preliminary 137 fb (13 TeV) statistical significances for the WZ 104 t ion s. Thus, t he st ud y of V BS pro cesses a n d Z Z pr o c e s s e s a r e 6.8 a n d 4.0 s t a n d- provides key insight into the quartic Z + X ard deviations, respectively, in line – gauge couplings as well as the Higgs 103 ttZ, VVZ with the expected SM significances of mjj > 100 GeV s e c t or. T h e s e pr o c e s s e s o ffe r s e n s it i v it y qq– → ZZ 5.3 and 3.5 standard deviations. The to enhancements caused by models of gg → ZZ possible presence of anomalous quar- physics beyond the SM, which modify 102 EW ZZjj tic gauge couplings could result in t he Higgs sector w it h addit ional Higgs data an excess of events with respect to bosons contributing to VBS. the SM predictions. Strong new con- Vector-boson scattering is character- 10 straints on the structure of quartic ised by the presence of two forward jets, events/0.04 gauge couplings have been set within with a large di-jet invariant mass and the framework of dimension-eight • Full Beamline Solutions a large rapidity separation. CMS pre- 1 effective-field-theory operators. viously reported the first observation The observation of the EW produc- • Accelerator and Neutron Instrumentation of same-sign W ±W± production using tion of W±W±, WZ and ZZ boson pairs –1 the data collected in 2016. The same- 10 is an essential milestone towards • Monochromator and Mirror Systems sign W±W± process is chosen because pre cision tests of VBS at the LHC,

of the smaller background yield from 3 sobs = 4.0σ and there is much more to be learned • High Stability Cryo Coolers other SM processes compared to the from the future LHC Run-3 data. The 1 opposite-sign W± W  process. The High-Lumin osity LHC should allow for data/bkgd. • Experimental Stations collaboration has now updated this very precise investigations of VBS, Sub-20nrad 00.2 0.40.6 0.81.0 analysis and performed new studies including finding evidence for the Stability Achieved KD • Insertion Devices of the EW production of two jets pro- scattering of longitudinally polarised duced in association with WZ, and Fig. 1. Distributions of the boosted-decision-tree score in the WZ W bosons. Two Horizontal-Bounce Cryo-Cooled DCMs • Professional Engineering Support for Diamond Light Source DLS ZZ boson pairs using data collected signal region (top) and the matrix-element discriminant in the ZZ between 2016 and 2018 at a centre- signal region (bottom). The lower panels show the ratios of data to Further reading of-mass energy of 13 TeV, correspond- the SM and background-only predictions, respectively. The grey CMS Collab. 2020 arXiv:2005.01173. ing to 137 fb–1. Vector-boson pairs were band shows the uncertainty on the predicted yields. The grey line is CMS Collab. 2020 CMS-PAS-SMP-20-001. selected by their decays to electrons the ratio of the total fit to its background-only component. CMS Collab. 2020 CMS-PAS-SMP-19-014. Axilon AG • Emil-Hoffmann Str. 55-59 • 50996 Köln • Germany • +49 (221) 165 324 00 • [email protected] • www.axilon.de

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ENERGY FRONTIERS ENERGY FRONTIERS

L a common core source with a Gaussian size, indicating a common emission source This result is This observation can be exploited by coa- shape. The core source was then folded for all baryons. The observed scaling of the a milestone lescence models studying the production is very similar to that 3He, L interrogates 32 line shape with the exponential tails introduced by source size with mT i n t he fie ld of of light nuclei, such as deuterons or the resonance decays. The resulting root- observed in heavy-ion collisions, wherein in hadronic collisions. Moreover, the correlation mean-square width of the Gaussian core the effect is attributed to the collective femtoscopy formalism relates the emis- In 2003 the Belle collaboration reported limit from Belle (see fi g ure). scales from 1.3 fm to 0.85 fm as a function evolution of the system. studies sion source to the interaction potential the discovery of a mysterious new hadron, Combining the two analyses, the of an increase in the pair’s transverse T h i s r e s u l t i s a m i l e s t o n e i n t h e fie l d o f between pairs of particles, enabling the LHCb B+ → χ (3872)K+ the X(3872), in the decay B → X(3872)K . c1 mass of the χc1(3872) was found to be mass (mT) from 1.1 to 2.2 GeV, for both p–p correlation studies, as it directly relates study of the strong nuclear force between Their analysis suggested an extremely 3871.64 ± 0.06 MeV – just 70 ± 120 keV and p–Λ p a i r s (s e e fi g u r e). T h e t r a n s v e r se to important topics in physics. The com- hadrons, such as p–K–, p–Ξ–, p–Ω– and LHCb b → χc1 (3872)X – small width, consistent with zero, and below the 00 threshold. The prox- mass of a particle is its total energy in a mon source size observed for p–p and p–Λ Λ–Λ, with unprecedented precision.

a mass remarkably close to the sum of Belle B → χc1 (3872)K imity of the χc1(3872) to this threshold coordinate system in which its velocity is pairs implies that the spatial- temporal the masses of the 0 and 0 mesons. The puts a uestion mark on measuring the zero along the beam axis. The two systems properties of the hadronisation process Further reading BES III e+e– → χ (3872)γ par t ic le’s e x istence w as later confi r med c1 w id t h u s i n g a s i m pl e fi t t o t h e w e l l-k n o w n exhibit a common scaling of the source are independent of the particle species. ALICE Collab. 2020 arXiv:2004.08018. by the CF, 0 and BaBar experiments. Breit–Wigner function, as this approach BaBar B → χc1 (3872)K L HC b fi r s t r e p or t e d s t u d i e s o f t h e X(3872) neglects potential distortions. Conversely, ATLAS in the data sample taken in 2010, and later BaBar B → χc1 (3872)K a precise measurement of the line shape unambiguously determined its uantum could help elucidate the nature of the LEP-era universality discrepancy unravelled numbers to be 1 , leading the Particle ata 0 1 234 5 χc1(3872). This has led LHCb to explore a Group to change the name of the particle [MeV] more sophisticated Flatt parametrisation The family of charged leptons is com- lifetime and its lower momentum decay Γχc1(3872) to χc1(3872). and report a measurement of the χc1(3872) posed of the electron, muon (μ) and tau ATLAS preliminary data products are exploited by the precise 6 –1 The nature of this state is still unclear. line shape with this model, including the lepton (τ). According to the Standard 10 √s = 13 TeV, 139 fb prompt μ (top) muon reconstruction available from the signal region ntil now, only an upper limit on the width l a p pi n g d a t a s e t s. T h e fi r s t u s e s R u n-1 d a t a Fig. 1. Ne Cb pole positions of the complex amplitude. Model (SM), these particles only differ 5 τ → μ (top) ATLAS detector to separate muons from 10 eμ, 20 < pμ < 250 GeV of the (3872) of 1.2 MeV has been avail- corresponding to an integrated luminosity constraints on the The results favour the interpretation of in their mass: the muon is heavier than T μ (hadron decay) tau-lepton decays and muons produced χc1 post-fit –1 3 0–0 4 Z → ττ able. No conventional hadron is expected of 3 fb , in which (15.5 ± 0.4) × 10 χc1(3872) reitigner idth the state as a uasi-bound mole- the electron and the tau lepton is heavier 10 directly by a W decay (so-called prompt other SM processes to have such a narrow width in this part of particles were selected inclusively from of the χc1( cule, but other possibilities cannot yet be than the muon. A remarkable feature of muons). Specifically, the absolute distance 3 uncertainty the otherwise very well understood char- the decays of hadrons containing b state (red and ruled out. Further studies are ongoing. the SM is that each flavour is equally likely 10 of closest approach of muon tracks in the μ monium spectrum. Among the possible uarks. The second analysis selected preious upper Physicists from other collaborations are to interact with a W boson. This is known 2 plane perpendicular to the beam line, |d0| 3 10 explanations are that it is a tetrauark, (4.23 ± 0.07) × 10 fully reconstructed limits at the 0 also keenly interested in the nature of the as lepton flavour universality. (a s s h o w n i n t h e t o p fi g u r e), a n d t h e t rans- μ a molecular state, a hybrid state where B → χc1(3872)K decays from the full Run confi dence level. χc1(3872), and the very recent observation In a new ATLAS measurement, a novel 10 verse momentum, pT, of the muons, are 0 the gluon fi eld contributes to its quan- 1–2 data set, which corresponds to an inte- The orange band by CMS of the decay process Bs →χc1(3872)φ technique using events with top-quark used to isolate these contributions. These tum numbers, or a glueball without any grated luminosity of 9 fb–1. In both cases, shos the aerage suggests another laboratory for studying pairs has been exploited to test the ratio of variables, in particular |dμ|, are calibrated 1.05 0 valence uarks at all. A mixture of these the χc1(3872) particles were reconstructed of the to Cb its properties. probabilities for tau leptons and muons to 1.00 using a pure sample of prompt muons – explanations is also possible. t hrough decays to t he fi na l state J/ψπ π . measurements. be produced in on-shell W boson decays, 0.95 from Z → μμ data. The LHCb collaboration has now pub- For the first time the measured Breit– Further reading R(τ/μ). In the SM, R(τ/μ) is expected to be data/pred. events/0.01 mm The extraction of R(τ/μ) is performed 0 0.1 0.2 0.3 0.4 0.5 μ μ lished two new measurements of the width Wigner width was found to be non-zero, LHCb Collab. 2020 arXiv:2005.13419. unity, but a longstanding tension with μ usi ng a fit to |d 0| and pT, where the can- |d0| [mm] of the χc1(3872), based on minimally over- with a value close to the previous upper LHCb Collab. 2020 arXiv:2005.13422. this prediction has existed since the LEP cellation of several systematic uncertain- era in the 1990s, where, from a combina- ties is observed as they are correlated AL to study the baryon–baryon interaction, tion of the four experiments, R(τ/μ) was ATLAS preliminary LEP (Phys. Rept. 532 119) between the prompt μ and τ → μ con- 1.4 and would impose strong constraints on measured to be 1.070 ± 0.026, deviating tributions. This includes uncertainties ommon aryon ALICE pp √s = 13 TeV √s = 13 TeV, ATLAS – this result particle-production models. from the SM expectation by 2.7σ. This –1 r e l a t e d t o j e t r e c o n s t r u c t i o n, fl a v o u r t ag- 1.3 high-mult. (0 0.17− % INEL > 0) 139 fb statistical error The ALICE collaboration has recently strongly motivated the need for new g i n g a n d t r i g g e r e ffic i e n c i e s. A s a r e s u lt, source ound in Gaussian + resonance source systematic error 1.2 used p–p and p–Λ pairs to perform the measurements with higher precision. If total error the measurement obtains very high proton collisions fi r s t s t u d y o f t h e p a r t i c l e- e m it t i n g s o u r c e the LEP result was confirmed it would precision, surpassing that of the previous 1.1

(fm) for baryons produced in pp collisions. The correspond to an unambiguous discovery LEP measurement. core

High-energy hadronic collisions, such as r 1.0 chosen data sample isolates the 1.7 per- of beyond-the-SM physics. The measured value is R(τ/μ) = 0.992 those delivered by the LHC, result in the p–p mille highest-multiplicity collisions in To conclusively prove either that the ± 0.013 [± 0.007 (stat) ± 0.011 (syst)], form- 0.9 0.98 1.00 1.02 1.04 1.06 1.08 1.11 production of a large number of particles. the 13 TeV data set, yielding events with LEP discrepancy is real or that it was just ing the most precise measurement of this p–Λ (NLO) R(τ/μ) = BR(W→τν)/BR(W→μν) Particle pairs produced close together in 0.8 30 to 40 charged particles reconstructed, a st at ist ic a l fluc t uat ion, a prec ision of at ratio, with an uncertainty half the size of p–Λ (LO) μ both coordinate and momentum space on average, per unit of rapidity. The yields least 1–2% is required – somet hing pre- Fig. 1. Top: an example |d0| distribution (in the electron tagging that from the combination of LEP results 0.7 μ are subject to fi nal-state eff ects, such as of protons and Λ baryons are dominated by viously not thought possible at a hadron channel for the highest pT bin) after the fit to data has been (s e e b o t t o m fi g u r e). T h i s i s i n a g r e e m e nt uantum statistics, Coulomb forces and, 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 contributions from short-lived resonances, collider like the LHC, where inclusive W performed, showing the separation power between prompt μ and with the Standard Model expectation and

in the case of hadrons, strong interac- 〈mT〉 (GeV) accounting for about two thirds of all pro- b o s o n s, a l b e it pr o d u c e d a b u n d a nt l y, s u ffe r τ → μ contributions. Bottom: a comparison of this measurement suggests that the previous LEP discrep- tions. Femtoscopy uses the correlation duced particles. A basic thermal model (the from large backgrounds and kinematic to that from LEP. The vertical dashed line indicates equal anc y may be due to a fluct uat ion. of such pairs in momentum space to gain Fig. 1. The aussian core radius as a function of the transerse statistical hadronisation model) was used biases due to the online selection in the branching ratios (SM value) to different lepton flavours. Though surviving this latest test, the insights into the interaction potential mass of the pp and pΛ pairs, extracted from femtoscopic fi ts to to estimate the number and composition trigger. The key to achieving this is to principle of lepton flavour universal- and the spatial extent of an effective the ALICE data. The scaling is observed independently of the of these resonances, indicating that the obtain a sample of muons and tau leptons W boson is used to select the events and ity will not quite be out of the woods particle-emitting source. interaction model used to describe the pΛ interaction (leading or average lifetime of those feeding to protons from W boson decays that is as insensitive the other is used, independently of the until the anomalies in B-meson decays Abundantly produced pion pairs are next-to-leading order chiral-eff ective-fi eld-theory calculations). (1.7 fm) is signifi cantly shorter than those as possible to the details of the trigger first, to measure the fractions of decays recorded by the LHCb experiment (CERN used to assess the size and evolution of feeding to Λ baryons (4.7 fm) – this would and object reconstruction used to select to tau leptons and muons. Courier May/June 2020 p10) have also been the high-density and strongly inter- heavy-ion collisions, motivating detailed have led to a substantial broadening of them. ATLAS has achieved this by exploit- The analysis focuses on tau-lepton definitively probed. acting uark–gluon plasmas, which are investigations of the particle source in the source shape if not properly accounted ing both the LHC’s large sample of more decays to a muon, rather than hadronic for m e d i n h e a v y-i o n c ol l i s i o n s. R e c e nt l y, such systems as well. A universal descrip- for. An explicit treatment of the eff ect of t h a n 100 million top-quark pairs produced tau-lepton decays that are more compli- Further reading high-multiplicity pp collisions at the LHC tion of the emission source for all baryon short-lived resonances was developed in the latest run, and the fact that top cated to reconstruct, thus reducing the ATLAS Collab. 2020 ATLAS-CONF-2020-014. have raised the possibility of observing s p e c ie s, i n d e p e n d e nt o f t h e s p e c i fi c q u a r k by assuming that all primordial parti- q u a r k s d e c a y e x c lu s i v e l y t o a W b o s o n a n d systematic uncertainties associated with LEP Electroweak Working Group 2013 ▲ c ol l e c t i v e e ff e c t s s i m i l a r t o t h o s e s e e n i n composition, would open new possibilities cles and resonances are emitted from a quark. In a tag-and-probe approach, one object reconstruction. The tau-lepton Phys. Rept. 532 119; arXiv:1302.3415.

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CCJulAug20_EnergyFrontiers_v3.indd 18 22/06/2020 19:01 CCJulAug20_EnergyFrontiers_v3.indd 19 22/06/2020 19:03 CERNCOURIER www. V o l u m e 6 0 N u m b e r 4 J u l y /A u g u s t 2 0 2 0 Mass spectrometers for vacuum, gas, plasma and surface science CERNCOURIER.COM FIELD RGA Series NOTES Residual Gas Analysers Reports from events, conferences and meetings IPAC’20 3F Series RGA IPAC goes virtual Triple fi lter mass spectrometers More than 3000 accelerator specialists IPAC’2020 gathered in cyberspace from 11 to 14 May for analytical applications for the 11th International Particle Accel- erator Conference (IPAC). The conference Triple filter technology provides extended was originally destined for the GANIL mass ranges, increased mass resolution, laboratory in Caen, a charming city in Normandy, and host to the flagship enhanced sensitivity and improved radioactive-ion-beam facility SPIRAL-2, contamination resistance for more but the coronavirus pandemic forced the cancellation of the in-person meeting demanding analytical applications. and the French institutes CNRS/IN2P3, CEA/IRFU, GANIL, Soleil and ESRF agreed to organise a virtual conference. Oral presentations and the accelerator-prize HAL 101X session were maintained, though unfor- tunately the poster and industry sessions had to be cancelled. The scientific pro- For beam line/torus fusion research gramme committee whittled down more than 2000 proposals for talks into 77 The seven IPAC’20 presentations Live around pioneered at SSRL. Stressing the value Unique radiation hardened mass spectrometer presentations, which garnered more than with the most views included four by the world of international collaboration, Hastings for operation in harsh radiation environments 43,000 video views across 60 countries, outstanding female scientists. CERN A selection of more presented the outcome of an international making IPAC’20 an involuntary pioneer Director-General Fabiola Gianotti pre- than 3000 X-ray facilities meeting that took place such as beam lines and synchrotrons with of virtual conferencing and a lighthouse sented strategic considerations for future registered in April and defined an action plan for remote analyser mounting up to 80m from of science during the lockdown. accelerator-based particle physics. While participants at ensuring the best possible support to sensitive electronics. pointing out the importance of Europe IPAC’20’s online COVID-19 research. Top of the talks participating in projects elsewhere in the closing session. GANIL director Alahari Navin pre- IPAC’20’s success relied on a programme world, she made the strong point that sented new horizons in nuclear science, of recent technical highlights, new devel- CERN should host an ambitious future reviewing facilities around the world and opments and future plans in the accel- collider, and discussed the options being presenting his own laboratory’s latest HALO 201 erator world. Weighing in at 1998 views, considered, pointing to the update of the activities. GANIL has now started com- the most popular talk of the conference European Strategy for Particle Physics missioning SPIRAL-2, which will allow was by Ben Shepherd from STFC’s Dares- soon to be approved by the CERN Council. users to explore the as-yet unknown For residual gas analysis bury Laboratory in the UK, who spoke on Sarah Cousineau from Oak Ridge reported properties of exotic nuclei near the lim- high-technology permanent magnets. on accelerator R&D as a driver for science its of the periodic table, and has per- Suitable for vacuum fingerprint analysis, Accelerators not only accelerate ensem- in general, pointing out that accelerators formed its initial science experiment. leak detection and trend analysis. bles of particles, but also use strong mag- h a v e d i r e c t l y c o nt r i b ut e d t o m or e t h a n 25 Liu Lin from LNLS in Brazil presented ne t ic fie ld s to g u id e a nd fo c u s t he m i nto Nobel prizes, including the Higgs-boson the commissioning results for the new very small volumes, typically just micro discovery at the LHC in 2012. The devel- fourth-generation SIRIUS light source, or nanometres in size. Recent trends opment of superconducting accelerator showing that the functionality of the indicate increasing usage of perma- technology has enabled projects for col- facility has already been demonstrated nent magnets t hat prov ide strong fields liders, photon science, nuclear physics by storing 15 mA of beam current. Last, but 3F-PIC but do not require external power, and and neutron spallation sources around not least in the top-seven most-viewed can provide outstanding field quality. the world, with several light sources and talks, Anke-Susanne Müller from KIT Describing the major advances for per- neutron facilities currently engaged in presented the status of the study for a Pulse ion counting detection manent magnets in terms of production, COVID-19 studies (see p43). 100 km Future Circular Collider – just one for fast event studies radiation resistance, tolerances and field The benefits of accelerator-based of the options for an ambitious post-LHC tuning, Shepherd presented high-tech photon science for society were also project at CERN. Ultra-fast pulse ion counting detection devices developed and used for the SIR- emphasised by Jerry Hastings from Stan- Recent trends Many other highlights from the IUS, ESRF–EBS, SPRING-8, CBETA, SOLEIL ford University and SLAC, who presented accelerator field were presented during provides seven decade continuous dynamic indicate and CUBE-ECRIS facilities, and also pre- the tremendous progress in structural increasing IPAC’20. Kyo Shibata (KEK) discussed range with optimum sensitivity at UHV/XHV. sented the Zero-Power Tunable Optics biology driven by accelerator-based the progress in physics data-taking at (ZEPTO) collaboration between STFC and X-ray sources, and noted that research usage of the SuperKEKB factory, where the Belle CERN, which offers 15–60 T/m tunability can be continued during COVID-19 times permanent II experiment recently reported its first in quadrupoles and 0.46–1.1 T in dipoles. thanks to the remote synchrotron access magnets result. Ferdinand Willeke (BNL) presented

W www.HidenAnalytical.com E [email protected] CERN COURIER JULY/AUGUST 2020 21

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FIELD NOTES FIELD NOTES

the electron–ion collider approved to be accelerator-applications session rounded To the credit of the French organis- pr o c e s s. T h e o b s e r v e d s i g n a l s i g n i fic a n c e The first width of the resonance (see p18). Though ons. The results from this measurement built at BNL, Porntip Sudmuang (SLRI) the picture off with presentations by ers, the virtual setup worked seamlessly. was found to be 4.3 standard deviations, observation of the results favour its interpretation as a can be used in propagation models of 0–*0 showed construction plans for a new Annalisa Patriarca (Institut Curie) on The concept relied on pre-recorded pres- in excess of the expected sensitivity the combined quasi-bound D D molecule, more data antideuterons within the interstellar light source in Thailand, and Mohammad accelerator challenges in a new radia- entations and a text-driven chat function of 2.4, assuming SM four-top-quark- and additional analyses are needed to medium for interpreting dark-matter production of Eshraqi (ESS) discussed the construc- tion-therapy technique called FLASH, that allowed registered participants to production properties. While the meas- rule out other hypotheses. searches, including intriguing results tion of the European Spallation Source in in which ultra-fast delivery of radiation join from time zones across the world. ured value of the cross section was found three massive from the AMS experiment. Future anal- Sweden. At the research frontier towards dose reduces damage to healthy tissue; Activating the sessions in half-day steps to be consistent with the SM prediction vector bosons ALICE and the dark sector yses with higher statistics will improve compact accelerators, Chang Hee Nam by Charlotte Duchemin (CERN) on the preserved the appearance of live pres- within 1.7 standard deviations, the data was reported The ALICE collaboration presented a first the modelling and extend these studies (IBS, Korea) explained prospects for production of non-conventional radi- entations to some degree, before a final collected during Run 3 will shed further by CMS measurement of the inelastic low-energy to heavier antinuclei. laser-driven GeV–electron beams from onuclides for medical research at the live session, during which the four prizes light on this rare process. antideuteron cross section using p–Pb The above are just a few of the many pl a s m a-w a k e fie l d a c c e l e r a t or s a n d A rnd SPIR A L-2 w ill MEDICIS hadron-beam facility; by Toms of the accelerator group of the European The LHCb collaboration presented, collisions at a centre-of-mass energy excellent results that were presented at Specka (LLR/CNRS) showed plans for the Torims (Riga Technical University) on Physical Society were awarded. with unprecedented precision, meas- per nucleon–nucleon pair of 5.02 TeV. LHCP’20. The extraordinary performance explore exotic compact European plasma-accelerator the treatment of marine exhaust gases urements of two properties of the Low-energy antideuterons (composed of the LHC coupled with progress reported facility EuPRAXIA, which is entering nuclei near the using electron beams; and by Adrian Mike Seidel PSI and EPFL, mysterious X(3872) particle. Originally of an antiproton and an antineutron) by the theory community, and the its next phase after successful comple- limits of the Fabich (SCK–CEN) on proton-driven Ralph Aßmann DESY and discovered by the Belle experiment in are predicted by some models to be a excellent data collected by the exper- tion of a conceptual design report. The periodic table nuclear-waste transmutation. Frédéric Chautard GANIL. 2003 as a narrow state in the J/ψπ+π– mass promising probe for indirect dark-mat- iments, has inspired LHC physicists spectrum of B+ → J/ψπ+π–K+ decays, this ter searches. In particular, antideuterons to continue with their rich harvest of LHCP ConferenCe particle has puzzled particle physicists could be produced during the annihila- physics results, despite the current world ever since. The nature of the state is still tion or decay of neutralinos or sneutrinos, crisis. Results presented at the confer- unclear and several hypotheses have which are hypothetical dark-matter can- ence showed that huge progress has LHC physics shines amid COVID-19 crisis been proposed, such as it being an exotic didates. Contributions from cosmic-ray been made on several fronts, and that tetraquark (a system of four quarks interactions in the low-energy range Run 3 and the High-Luminosity LHC LHCP The eighth Large Hadron Collider Physics bound together), a two-quark hadron, b e low 1–2 GeV per nucleon are expected upgrade programme will enable fur- (LHCP) conference, originally scheduled or a molecular state consisting of two D to be small. ALICE collaborators used a ther exploration of particle physics at to be held in Paris, was hosted as a fully mesons. LHCb collaborators reported the novel technique that utilised the detector the energy frontier. online conference from 25 to 30 May. To most precise mass measurement yet, and material as an absorber for antideuterons enable broad participation, the organ- m e a s u r e d, for t h e fi r s t t i m e, a n d w it h fi ve to measure the production and annihi- Tulika Bose University of isers waived the registration fee and, standard-deviations significance, the lation rates of low-energy antideuter- Wisconsin-Madison. with the help of technical support from CERN, hosted about 1300 registered participants from 56 countries, with attendees actively engaging via Zoom webinars. Even a poster session was possible, with 50 junior attendees from all over the world presenting their work via meeting rooms and video recordings. The organisers must be complimented for organising a pioneering virtual simultaneous production of three mas- Brainpower ment with SM predictions, more data is conference that succeeded in bringing sive vector bosons has eluded us so far, as A cross section of needed for the individual measurements the LHC community together, in larger the cross sections are small and the back- online delegates at of the WZZ and ZZZ processes. and more diverse numbers than at ground contributions are rather large. LCHP 2020. The first evidence for four-top-quark previous editions. Such measurements are crucial, both to production was announced by ATLAS. The test the underlying theory and to probe top-quark discovery in 1995 launched a Enhanced sensitivity non-standard interactions. For example, rich programme of top-quark studies LHCP’20 presentations covered a wide if new physics beyond the SM is present at that includes precision measurements assortment of topics and several new high mass scales not far above 1 TeV, t hen of its properties as well as the observa- results with significantly enhanced cross-section measurements for tribo- tion of single-top-quark production. In sensitivity than was previously possible. son final states might deviate from SM particular, since the large mass of the top These included both precision measure- predictions. The CMS experiment took quark is a result of its interaction with ments with excellent potential to uncover advantage of the large Run-2 dataset and the Higgs field, studies of rare processes discrepancies that can be explained only machine-learning techniques to search such as the simultaneous production of by physics beyond the Standard Model for these rare processes. Leveraging the four top quarks can provide insights into (SM) and direct searches using innova- r e l a t i v e l y b a c k g r o u n d-f r e e l e p t o n i c fi n a l the properties of the Higgs boson. Within tive techniques and advanced analysis states, CMS collaborators were able to the SM, this process is extremely rare, methods to look for new particles. combine searches for different decay occurring just once for every 70,000 pairs T h e fi r s t o b s e r v a t io n o f t h e c o m bi ned modes and different types of triboson of top quarks created at the LHC; on the production of three massive vector bos- production (WWW, WWZ, WZZ and ZZZ) other hand, numerous extensions of the ons (VVV with V = W or Z) was reported to achieve the first observation of com- SM predict exotic particles that couple to by the CMS experiment (see also p17). In bined heavy triboson production (with t o p q u a r k s a n d l e a d t o s i g n i fic a nt l y h i g h e r the nearly 40 years that have followed a n o b s e r v e d s i g n i fic a n c e o f 5.7 s t a n d a rd production rates. The ATLAS experiment the discovery of the W and Z boson, their deviations), and at the same time evi- performed this challenging measurement properties have been measured very pre- dence for WWW and WWZ production using the full Run-2 dataset using sophis- cisely, including via “diboson” measure- w it h o b s e r v e d s i g n i fic a n c e s o f 3.3 a n d 3.4 ticated techniques and machine-learning ments of the simultaneous production of standard deviations, respectively. While m e t h o d s a p pl i e d t o t h e m u l t i l e p t o n fi n a l two vector bosons. However, “triboson” the results obtained so far are in agree- state to obtain strong evidence for this

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FEATURE GNOME SENSING A PASSAGE THROUGH THE UNKNOWN A global network of ultra-sensitive optical atomic magnetometers – GNOME – has begun its search for exotic fields beyond the StandardModel.

Long shot Previous precision measurements could have ,, ,.... "' missed exotic transient phenomena. -2 -1 0 1 2 3 Input Power {dBm)

IOP Concise Physics A Morgan & Claypool Publication A Modern Introduction to EDITOR’S Shutterstock/bluebay A Modern Introduction PICK Neutrino Physics ince the inception of the Standard Model (SM) of decades are not effects that persist over the many weeks to Neutrino Physics particle physics half a century ago, experiments of or mont hs of a t y pical measurement campaig n, but rat her Frank F Deppisch Frank F Deppisch Sall shapes and sizes have put it to increasingly strin- t r a n s ie nt e v e nt s t h at o c c u r o n l y s p or a d ic a l l y? For e x a m ple, gent tests. The la rgest a nd most wel l-k now n a re col l ider might not cataclysmic astrophysical events such as black- A deeper understanding of neutrinos, with the goal to reveal their nature and exact role within experiments, which in particular have enabled the direct hole mergers or supernova explosions produce hypothet- particle physics, is at the frontier of current research. This book reviews the field in a concise discovery of various SM particles. Another approach utilises ical ultralight bosonic fields impossible to generate in the fashion and highlights the most pressing issues, in addition to the strongest areas of topical the tools of atomic physics. The relentless improvement in laboratory? Or might not Earth occasionally pass through interest. The text provides a clear, self-contained, and logical treatment of the fundamental t h e pr e c i s io n o f t o ol s a n d t e c h n iq ue s o f at o m ic p h y s ic s, b o t h some invisible “cloud” of a substance (such as dark matter) physics aspects appropriate for graduate students. e x p e r i m e nt a l a n d t h e or e t ic a l, h a s le d t o t h e v e r i fic at io n o f produced in the early universe? Such transient phenomena t h e S M’s pr e d ic t io n s w it h e v e r g r e at e r a c c u r a c y. E x a m ple s c o u ld e a s i l y b e m i s s e d b y e x p e r i m e nt e r s w h e n d at a a r e a v e r- Frank Deppisch earned his undergraduate qualification in physics at the University of include measurements of atomic parity violation that reveal a ge d over long t i me s to i nc rea s e t he sig n a l-to-noi s e r at io. Würzburg, where he also worked as a doctoral student and research assistant, and completed THE AUTHORS t h e e ffe c t s o f t h e Z b o s o n o n at o m ic s t at e s, a n dmeasur- Detecting such unconventional events represents his doctoral thesis. He is an associate professor within the high energy physics group at Dmitry Budker m e nt s o f at o m ic e n e r g y le v e l s t h at v e r i f y t h e pr e d ic t io n s o f several challenges. If a transient signal heralding new University College London and he worked as a member of the ATLAS collaboration at the Johannes Large Hadron Collider at CERN. quantum electrodynamics (QED). Precision atomic physics physics was observed with a single detector, it would Gutenberg e x p e r i m e nt s a l s o i n c lud e a v a s t a r r a y o f s e a rc h e s for e ffe c t s be exceedingly difficult to confidently distinguish the University and pr e d ic t e d b y t h e or ie s b e yo n d-t h e-S M (B S M), s uc h a s fi f t h exotic-physics signal from the many sources of noise that University of forc e s a n d p e r m a n e nt e le c t r ic d i p ole m o m e nt s t h at v iol at e pl a g ue pr e c i s io n at o m ic p h y s ic s m e a s u r e m e nt s. Ho w e v e r, California, parity- and time-reversal symmetry. These tests probe i f t r ansient inter act ions occur over a global scale, a net- Derek Jackson Kimball To access this title, visit iopscience.org/books. If you have an idea for a book that you’d like to discuss, potentially subtle yet constant (or controllable) changes of work of such detectors geographically distributed over California State atomic properties that can be revealed by averaging away Earth could search for specific patterns in the timing and please e-mail [email protected]. University and noise and controlling systematic errors. amplitude of such signals that would be unlikely to occur Szymon Pustelny But what if the glimpses of BSM physics that atomic spec- r a n d o m l y. B y c or r e l at i n g t h e r e a d o ut s o f m a n y d e t e c t or s, Jagiellonian troscopists have so painstakingly searched for over the past lo c a l e ffe c t s c a n b e fi lt e r e d a w a y a n d e x o t ic p h y s ic scould University.

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FEATURE GNOME FEATURE GNOME A Wickenbrock Mainz, Germany topological defect magnetic signals transient detector M Longnickel Jena, Germany exotic field 1. Berkeley, US

pump collaborationGNOME Lewisburg, light Berkeley, PA, US Krakow, Poland 2. Lewisburg, US CA, US Beijing, China atomic vapour 4 5 Hayward, Oberlin, 6 3. Oberlin, US CA, US OH, US Daejeon, South Korea 1 velocity Hefei, China 4. Daejeon, US Los Angeles, polarisation rotation 2 8 3 CA, US 7 5. Beijing, China

Canberra, Australia spin precession 6. Hefei, China Fribourg, Be’er Sheva, Switzerland 7. Mainz, Germany Israel probe light 8. Krakow, Poland Correlated be distinguished from mundane physics. Optical rotation In a GNOME optical atomic magnetometer, time now The Global This idea forms the basis for the Global Network of Optical linearly polarised light optically pumps atomic-spin Network of Optical Magnetometers to search for Exotic physics (GNOME), an alignment along the light polarisation axis, making the Magnetometers to international collaboration involving 14 institutions from atomic vapour optically anisotropic. If a transient torque from Benchtop physics The OAM setup at the GNOME station at photons. There is even a possibility of exotic spin-0 or New domains search for Exotic all over the world (see “Correlated” figure). Such an idea, an exotic field causes the spins to precess, the axis of the optical California State Universit y – East Bay in Hay ward, California. s pi n-1 g r a v it o n s: w h i le t h e g r a v it o n for a q u a nt u m t h e or y An artist’s physics (GNOME) like so many others in physics, is not entirely new. The anisotropy, parallel to the spin alignment, also rotates. This of gravity matching that described by general relativity rendition of the is specifically same concept is at the heart of the worldwide network of causes optical rotation of the light polarisation, which can be c ol l a b or at io n’s s e a rc h e ffor t s, a r e u lt r a l i g ht b o s o n ic fie lds. must be spin-2, alternative gravity theories (for example Earth passing designed to search interferometers used to observe gravitational waves (LIGO, precisely measured with a polarimeter. A canonical example of an ultralight boson is the axion. torsion gravity and scalar-vector-tensor gravity) predict through a for global-scale Virgo, GEO, KAGRA, TAMA, CLIO), and the global network The axion emerged from an elegant solution, proposed additional spin-0 and/or spin-1 gravitons. topological defect transient or of proton-precession magnetometers used to monitor geo- dependent energy shifts by controlling and monitoring an by Roberto Peccei and Helen Quinn in the late 1970s, to It a l s o t u r n s o ut t h at s uc h u lt r a l i g ht b o s o n s c o u ld e x pl a i n of an axion-like oscillating events magnetic and solar activity. What distinguishes GNOME ensemble of atomic spins via angular momentum exchange the strong–CP problem. The Peccei–Quinn mechanism dark matter. Most searches for ultralight bosonic dark field in the form of resulting from f r o m o t h e r g lo b a l s e n s or n e t wor k s i s t h at it i s s p e c i fic a l l y between the atoms and light. The high efficiency of optical e x pl a i n s t h e m y s t e r y o f w h y t h e s t r o n g i nt e r a c t io n, t o t h e matter assume the bosons to be approximately uniformly a “domain wall” the coupling dedicated to searching for signals from BSM physics that pumping and probing of atomic spin ensembles, along with highest precision we can measure, respects the combined distributed throughout the dark matter halo that envelopes (left). As various between atomic have evaded detection in earlier experiments. a wide array of clever techniques to minimise atomic spin CP symmetry whereas quantum chromodynamics naturally the Milky Way. However, in some theoretical scenarios, GNOME stations spins and GNOME is a growing network of more than a dozen relaxation (even at high atomic vapour densities), have a c c o m m o d at e s C P v iol at io n at a le v e l t e n ord e r s o f m a g n i- the ultralight bosons can clump together into bosonic pass through the beyond-the- optical atomic magnetometers, with stations in Europe, enabled OAMs to achieve sensitivities to spin-dependent t ud e l a r g e r t h a n pr e s e nt c o n s t r a i nt s. I f C P v iol at io n i n t h e “stars” due to self-interactions. In other scenarios, due topological defect, Standard-Model North America, Asia and Australia. The project was pro- energy shifts at levels well below 10–20 eV after only one strong interaction can be described not by a constant term to a non-trivial vacuum energy landscape, the ultralight signals appear in fields. posed in 2012 by a team of physicists from the University of second of integration. One of the 14 OAM installations, b ut r at h e r b y a d y n a m ic a l (a x io n) fie ld, it c o u ld b e s i g nif- b o s o n s c o u ld t a k e t h e for m o f “t o p olo g ic a l” d e fe c t s, s uc h a s the OAM data at California at Berkeley, Jagiellonian University, California at California State University – East Bay, is shown in the icantly suppressed by spontaneous symmetry breaking domaintopological walls defect that separate regions of spacemagnetic with signals different particular times State University – East Bay, and the Perimeter Institute. “Benchtop physics” image. at a high energy scale. If the symmetry breaking scale is vacuum states of the bosonic field (see “New domains” (right), normalised velocity The network started taking preliminary data in 2013, with However, one might wonder: do any of the theoretical at the grand-unification-theory (GUT) scale (~1016 GeV), figure). In either of these cases, the mass-energy1. Berkeley, USA associated so that the the first dedicated science-run beginning in 2017. With s c e n a r io s s u g g e s t i n g t h e e x i s t e n c e o f e x o t ic fie ld s pr e d ic t the axion mass is around 10-10 eV, and at the Planck scale with ultralight bosonic dark matter would be concentrated apparent signals 2. Lewisburg, USA more data on the way, the GNOME collaboration, consist- signals detectable by a magnetometer network while also (10 19 GeV) around 10-13 eV – b o t h m a n y ord e r s o f m a g n it ud e in large composite structures that Earth might only occa- have the same ing of more than 50 scientists from around the world, is evading all existing astrophysical and laboratory con- le s s m a s s i v e t h a n e v e n n e ut r i n o s. S e a rc h i n g for u lt r a l i g ht s io n a l l y e n c o u nt e r, le a d i n g t o t h e s or t o3. f Oberlin,t r a n s ieUSA nt s i g n a l s amplitude 1 presently combing the data for signs of the unexpected, straints? This is not a trivial requirement, since previous axions therefore offers the exciting possibility of probing t hat GNOME3 2 is desig ned to searc h for. and sign. 4. Daejeon, USA with its first results expected later this year. high-precision atomic spectroscopy experiments have physics at the GUT and Planck scales, far beyond the direct Yet another possibility7 8 is that intense bursts of ultra- e s t a bl i s h e d s t r i n g e nt l i m it s o n B S M p h y s ic s. I n f a c t, OA M reac h of any e x ist ing collider. light bosonic fields might be generated5 by cataclysmic 5. Beijing, China Exotic-physics detectors techniques have been used by a number of research groups astrophysical events such as black-hole6 mergers. Much Optical atomic magnetometers (OAMs) are among the most (including our own) over the past several decades to search Beyond the Standard Model of the underlying physics of coalescing4 6. Hefei, singularities China is sensitive devices for measuring magnetic fields. However, for spin-dependent energy shifts caused by exotic fields In addition to the axion, there are a wide range of other u n k n o w n, p o s s i bl y i n v ol v i n g q u a nt u m-g r a v it y e ffe c t s f a r 7. Mainz, Germany the atomic vapours that are the heart of GNOME’s OAMs sourced by nearby masses or polarised spins. Closely related h y p o t h e t ic a l u lt r a l i g ht b o s o n s t h at c o uple t o at o m ic s pi n s beyond the reach of high-energy experiments on Earth, are placed inside multi-layer shielding systems, reducing work has ruled out vast areas of BSM parameter space by and could generate signals potentially detectable with a n d it t u r n s o ut t h at q u a nt u m g r a v it y t h8. eKrakow, or ie s Polandg e n e r ic a l l y the effects of external magnetic fields by a factor of more c o m p a r i n g m e a s u r e m e nt s o f h y p e r fi n e s t r uc t u r e i n s i m ple GNOME. Many theories predict the existence of spin-0 bos- predict the existence of ultralight bosons. Furthermore, than a million. Thus, in spite of using extremely sensitive hydrogen-like atoms to QED calculations. Furthermore, if o n s w it h pr o p e r t ie s s i m i l a r t o t h e a x io n (s o-c a l le d a x io n- if ultralight bosons exist, they may tend to condensetime in now magnetometers, GNOME sensors are largely insensitive to exotic fields do exist and couple strongly enough to atomic l i k e p a r t ic le s, A L P s). A pr o m i n e nt e x a m ple i s t h e r e l a x io n, gravitationally bound halos around black holes. In these magnetic signals. The reasoning is that many BSM the- spins, they could cause noticeable cooling of stars and proposed by Peter Graham, David Kaplan and Surjeet Rajen- scenarios, a sizable fraction of the energy released when ories predict the existence of exotic fields that couple to affect the dynamics of supernovae. So far, all laboratory dran to explain the hierarchy problem: the mystery of why black holes merge could plausibly be emitted in t he form atomic spins and would penetrate through magnetic shields experiments have produced null results and all astro- the electroweak force is about 24 orders-of-magnitude of ultralight bosonic fields. If the energy density of the If such exotic largely unaffected. Since the OAM signal is proportional to physical observations are consistent with the SM. Thus stronger than the gravitational force. In 2010, Asimina ultralight bosonic field is large enough, networks of atomic fields exist, the spin-dependent energy shift regardless of whether or if such exotic fields exist, their coupling to atomic spins A r v a n it a k i a n d c ol le a g ue s fo u n d t h at s t r i n g t h e or y s u g g e s t s sensors li ke GNOME might be able to detect a sig nal. their coupling n o t a m a g n e t ic fie ld c a u s e s t h e e n e r g y s h i f t, OA M s – e vn must be extremely feeble. the existence of many ALPs of widely varying masses, from In order to use OAMs to search for exotic fields, the to atomic enclosed within magnetic shields – are sensitive to a broad Despite these constraints and requirements, theoret- 10-33 eV to 10-10 eV. From the perspective of BSM theories, effects of environmental magnetic noise must be reduced, spins must class of e xot ic fields. ical scenarios both consistent with existing constraints u lt r a l i g ht b o s o n s a r e u biq u it o u s. S o m e pr e d ic t A L P s s uc h controlled, or cancelled. Even though the GNOME mag- be extremely The basic principle behind OAM operation (see “Opti- a n d t h at pr e d ic t e ffe c t s m e a s u r a ble w it h GNOM E d o e x i s t. as “familons”, “majorons” and “arions”. Others predict netometers are enclosed in multi-layer magnetic shields feeble cal rotation” figure) involves optically measuring spin- Prime examples, and the present targets of the GNOME new ultralight spin-1 bosons such as dark and hidden so that signals from external electromagnetic fields are

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FEATURE GNOME SUPERCON, Inc. Afach Afach Particle and t h e s i g n a l s a p p e a r i n g i n d i ffe r e nt GNOM E m a g n e t o m e t e rs

50 2018 al. et 100 are proportional to S∙v. Both the signal-timing pattern and Superconducting Wire and Cable 0 0 the signal-amplitude pattern should be consistent with a nuclear physics Berkeley 1 –100 –50 single value of v; signals inconsistent with such a pattern Standard and Specialty designs are available to meet your most demanding Find the information you need from IOP Publishing’s 100 50 can be rejected as noise. superconductor requirements. 0 0 To claim discovery of a signal heralding BSM physics, world-leading journals and award-winning books Berkeley 2 –100 –50 detections must be compared to the background rate of SUPERCON,programme, along Inc. with conferencehas been proceedingsproducing and niobium-based superconducting wires and cables for half a century. 50 spurious false-positive events consistent with the expected science news from Physics World. 100 We are the original SUPERCON – the world’s first commercial producer of niobium-alloy based wire and 0 0 signal pattern but not generated by exotic physics. The Fribourg false-positive rate can be estimated by analysing time- cableiopscience.org/particle-and-nuclear-physics for superconducting applications. –100 –50 50 shifted data: the data stream from each GNOME magneto- δ B (pT) 100 m e t e r i s s h i f t e d i n t i m e r e l at i v e t o t h e o t h e r s b y a n a m o u nt Standard SC Wire Types Product Applications 0 0 Hayward much larger than any delays resulting from propagation NbTi Wires Magnetic Resonance Imaging –100 –50 of ultralight bosonic fields through Earth. Such time- 50 Nb3Sn —Bronze Nuclear Magnetic Resonance 100 shifted data can be assumed to be free of exotic-physics Nb3Sn —Internal Tin High Energy Physics 0 0 signals, so any detections are necessarily false positives: –100 Krakow –50 merely random coincidences due to noise. When the GNOME CuNi resistive matrix wires SC Magnetic Energy Storage 100 50 data are analysed without timeshifts, to be regarded as Fine diameter SC Wires Medical Therapeutic Devices 0 0 Aluminum clad wire Superconducting Magnets and Coils Mainz an indication of BSM physics, the signal amplitude must –100 –50 sur pass t he 5σ threshold as compared to the background Wire-in-Channel Crystal Growth Magnets 12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM 6:00 AM 12:00 PM 6:00 PM d e t e r m i n e d w it h t h e t i m e-s h i f t e d d at a. T h i s m e a n s t h at, 6/7/2017 6/7/2017 Innovative composite wires Scientific Projects date and time date and time for a year-long data set, an event due to noise coinciden- tally matching the assumed signal pattern throughout the net work would occur only once ever y 3.5 million years. “We deliver superconductivity!” Spurious signals significantly suppressed, there is a wide variety of phe- Sample data for nomena that can mimic the sorts of signals one would Inspiring efforts Contact us at [email protected] the apparent e x p e c t f r o m u lt r a l i g ht b o s o n ic fie ld s. T h e s e i n c lud e v i bra- Having already collected over a year of data, and with magnetic field tions, laser instabilities, and noise in the circuitry used more on the way, the GNOME collaboration is presently www.SUPERCON-WIRE.com deviation from the for data acquisition. To combat these spurious signals, combing the data for signs of BSM physics. New results mean (δB) from each GNOME station uses auxiliary sensors to monitor based on recent GNOME science runs are expected in 2020. ad.indd 1 28/03/2012 09:43 several GNOME electromagnetic fields outside the shields (which could This would represent the first ever search for such tran- stations. The blue leak inside the shields at a far-reduced level), accelerations sient exotic spin-dependent effects. Improvements in traces (left) show and rotations of the apparatus, and overall magnetometer magnetometer sensitivity, signal characterisation, and the raw data and performance. If the auxiliary sensors indicate data may be data-analysis techniques are expected to improve on these the red traces suspect, the data are flagged and ignored in the analysis initial results over the next several years. Significantly, (right) show the (see “Spurious sig nals” fig ure). GNOM E h a s i n s pi r e d s i m i l a r e ffor t s u s i n g o t h e r n e t wor ks Particle and data after GNOME data that have passed this initial quality check of precision quantum sensors: atomic clocks, interferom- high-pass and c a n t h e n b e s c a n n e d t o s e e i f t h e r e a r e s i g n a l s m at c h i n g t h e eters, cavities, superconducting gravimeters, etc. In fact, notch filters are p at t e r n s e x p e c t e d b a s e d o n v a r io u s e x o t ic p h y s ic s h y p o t h- the results of searches for exotic transient signals using nuclear physics applied to remove eses. For example, to test the hy pothesis that dark matter c lo c k n e t w or k s h a v e a l r e a d y b e e n r e p or t e d i n t h e l it e r at u r e, slow drifts and takes the form of ALP domain walls, one searches for a c o n s t r a i n i n g s i g n i fic a nt p a r a m e t e r s p a c e for v a r io u s B SM noise at line signal pattern resulting from the passage of Earth through scenarios. We would suggest that all experimentalists Find the information you need from IOP frequencies (50 or an astronomical-sized plane having a finite thickness given s h o u ld s e r io u s l y c o n s id e r a c c u r at e l y t i m e-s t a m pi n g, s t or- 60 Hz). An event by the ALP’s Compton wavelength. The relative velocity ing, and sharing their data so that searches for correlated Publishing’s world-leading journals and flagged by between the domain wall and Earth is unknown, but can signals due to exotic physics can be conducted a posteriori. award-winning books programme, along with auxiliary sensors be assumed to be randomly drawn from the velocity distri- O n e n e v e r k n o w s w h at n at u r e m i g ht b e h id i n g ju s t b e yo n d as spurious is b ut io n o f v i r i a l i s e d d a r k m at t e r, h a v i n g a n a v e r a g e s p e e d o f t he front ier of t he precision of past measurements.  conference proceedings and science news highlighted in a b o ut o n e t h o u s a n d t h t h e s p e e d o f l i g ht. T h e r e l at i v e t i m i n g from Physics World. green on the plots of signals appearing in different GNOME magnetometers Further reading of the data from should be consistent with a single velocity v: i.e. nearby S Afach et al. 2018 Phys. Dark Universe 22 162. Publish with us Hayward. stations (in the direction of the wall propagation) should D Budker and A Derev ian ko 2015 Phys. Today 68 10. d e t e c t s i g n a l s w it h s m a l le r d e l a y s a n d s t at io n s t h at a r e f a r C Dailey et al. 2020 arXiv:2002.04352. We offer a range of publishing options to suit your a p a r t s h o u ld d e t e c t s i g n a l s w it h l a r g e r d e l a y s, a n d f u r t h e r- A Derevianko and M Pospelov 2014 Nat. Phys. 10 933. needs, ensuring that your work gets the attention that more the time delays should occur in a sensible sequence. D F Jackson Kimball et al. 2018 Phys. Rev. D 97 043002. it deserves. The energy shift that could lead to a detectable signal in H Masia-Roig et al. 2020 Phys. Dark Universe 28 100494. GNOME magnetometers is caused by an interaction of the M Pospelov et al. 2013 Phys. Rev. Lett. 110 021803. domain-wall fieldφ w it h t h e at o m ic s pi n S w h o s e s t r e n g t h i s S Pustelny et al. 2013 Annalen der Physik 525 659. iopscience.org/particle-and-nuclear-physics proportional to the scalar product of the spin with the gra- B M Roberts et al. 2017 Nat. Commun. 8 1. d ie nt o f t h e fie ld, S∙∇φ. T h e g r a d ie nt o f t h e d o m a i n-w a l l fie ld M S Safronova et al. 2018 Rev. Mod. Phys. 90 025008. ∇φ is proportional to its momentum relative to S, and hence P Wcisło et al. 2016 Nat. Astron. 1 1.

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FEATURE NEUTRINOS TUNING IN TO NEUTRINOS A new generation of accelerator and reactor experiments is opening an era of high-precision neutrino measurements to tackle questions suchsuc h as leptoniclepton ic CP violation,v iolat ion, thet he mass hhierarchy ier a rc hy aand nd thet he possibilityp ossibi l it y of a fourthfour t h “sterile”“ster i le” neutrino,neut r i no, writesw r ites MarkM a rk Rayner.R ay ner.

n traditional Balinese music, instruments are made M Brice/CERN-PHOTO-201902-023-1 experiments span more than four orders of magnitude in in pairs, with one tuned slightly higher in frequency size and energy and fall into three groups (see “Not natural” than its twin. The notes are indistinguishable to the fi g u r e o n p3 4). M uc h o f t h e l i m e l i g ht i s t a k e n b y e x p e r iments I 2 human ear when played together, but the sound recedes that are sensitive to the large mass splitting ∆m32, which and swells a couple of times each second, encouraging include both a cluster of current (such as T2K) and future meditation. This is a beating effect: fast oscillations at (such as DUNE) accelerator-neutrino experiments with long the mean frequency inside a slowly oscillating envelope. b a s e l i n e s a n d h i g h e n e r g ie s, a n d a h i g h-p e r for m i n g t r io o f Similar physics is at play in neutrino oscillations. Rather r e a c t or-n e ut r i n o e x p e r i m e nt s (D a y a B a y, R E NO a n d D o u ble than sound intensity, it’s the probability to observe a neu- C h o o z) w it h a b a s e l i n e o f a b o ut a k i lo m e t r e, o p e r at i n g ju s t trino with its initial flavour that oscillates. The difference above the threshold for inverse beta decay. The second is how long it takes for the interference to make itself group is a beautiful pair of long-baseline reactor-neutrino felt. When Balinese musicians strike a pair of metallo- experiments (KamLAND and the soon-to-be-commissioned phones, the notes take just a handful of periods to drift JUNO), which join experiments with out of phase. By contrast, it takes more than 1020 de Broglie solar neutrinos in having sensitivity The zeitgeist wavelengths and hundreds of kilometres for neutrinos to t o t h e s m a l l e r s q u a r e d-m a s s s pl it t i n g 2 oscillate in experiments like the planned mega-projects ∆m21. Finally, the third group is a host began to shift to Hyper-Kamiokande and DUNE. of short-baseline accelerator-neutrino Neutrino oscillations revealed a rare chink in the armour experiments and very-short-base- artificially produced o f t h e St a n d a rd M o d e l: n e ut r i n o s a r e n o t m a s s le s s, b ut a r e line reactor neutrino experiments neutrinos evolving superpositions of at least three mass eigenstates that are chasing tantalising hints of with distinct energies. A neutrino is therefore like three a fourth “sterile” neutrino (with no n o t e s pl a y e d t o g e t h e r: f r e q ue n c ie s s o c lo s e, g i v e n t h e a s-y e t Standard-Model gauge interactions), which is split from immeasurably small masses involved, that they are not t h e o t h e r s b y a s q u a r e d-m a s s s pl it t i n g o f t h e ord e r o f 1 eV2. just indistinguishable to the ear, but inseparable accord- ing to the uncertainty principle. As neutrinos are always Artificial sources u lt r a-r e l at i v i s t ic, t h e e n e r g ie s o f t h e m a s s e i g e n s t at e s d i ffe r Experiments with artificial sources of neutrinos have a only due to tiny mass contributions of m2/2E. As the mass s t or ie d h i s t or y, d at i n g f r o m t h e 1950 s, w h e n p h y s ic i s t s t o y e d e i g e n s t at e s pr o p a g at e, p h a s e d i ffe r e n c e s d e v e lo p b e t w e en w it h t h e id e a o f d e t e c t i n g n e ut r i n o s c r e at e d i n t h e e x plo s io n them proportional to squared-mass splittings ∆m2. The o f a nuc le a r b o m b, a n d e v e nt u a l l y o b s e r v e d t h e m s t r e a m- sought-after oscillations range from a few metres to the ing from nuclear reactors. The 1960s saw the invention diameter of Earth. of the accelerator neutrino. Here, proton beams smashed into fixed targets to create a decaying debris of charged Orthogonal mixtures pions and their concomitant muon neutrinos. The 1970s The neutrino physics of the latter third of the 20th century transformed these neutrinos into beams by focusing the was bookended by two anomalies that uncloaked these c h a r g e d pio n s w it h m a g n e t ic h or n s, le a d i n g t o t h e d i s c o v e r y effects. In 1968 Ray Davis’s observation of a deficit of solar Golden opportunity Liquid-argon time-projection chambers can serve as both target and tracker for neutrino interactions. Here, an engineer is o f w e a k n e ut r a l c u r r e nt s a n d i n s i g ht s i nt o t h e s t r uc t u r e o f neutrinos prompted Bruno Pontecorvo to make public his pictured adjusting the charge-readout plane of the DUNE experiment’s dual-phase prototype detector at CERN. nuc le o n s. It w a s n o t u nt i l t h e t u r n o f t h e c e nt u r y, h o w e v e r, conjecture that neutrinos might oscillate. Thirty years that the zeitgeist of neutrino-oscillation studies began

later, the Super-Kamiokande collaboration’s analysis of “Little and large” figure, p34). It is not yet known ifν 3 is e nt r ie s, w h ic h c o u ld s i g n a l t he bre a k i n g of CP s y m me t r y,” to shift from naturally to artificially produced neutrinos. a deficit of atmospheric muon neutrinos from the other the lightest or the heaviest of the trio. This is called the s h e e x pl a i n s. “T h e v e r y d i ffe r e nt m i x i n g p at t e r n s i n q u arks Just a year after the publication of the Super-Kamiokande side of the planet posthumously vindicated the visionary mass-hierarchy problem. a n d le p t o n s c o u ld h i nt at a s y m m e t r y r e l at i n g f a m i l ie s, a n d collaboration’s seminal 1998 paper on atmospheric– Italian, and later Soviet, theorist’s speculation. Subsequent “In the first two decades of the 21st century we have a more accurate exploration of the lepton-mixing pattern neutrino oscillations, Japanese experimenters trained a observations have revealed that electron, muon and tau achieved a rather accurate picture of neutrino masses and and the neutrino ordering in future experiments will be new accelerator-neutrino beam on t he detector. neutrinos are orthogonal mixtures of mass eigenstates mixings,” says theorist Pilar Hernández of the University of essent ial to reveal any suc h sy mmet r y patter n.” Operating from 1999 to 2006, the KEK-to-Kamioka (K2K)

THE AUTHOR ν1 and ν2, separated by a small so-called solar splitting Valencia, “but the ordering of the neutrino states is unknown, To d a y, e x p e r i m e nt s d e s i g n e d t o c o n s t r a i n n e ut r i n o m i x- experiment sent a beam of muon neutrinos from the KEK 2 Mark Rayner ∆m21, and ν3, which is separated from that pair by a larger the mass of the lightest state is unknown and we still do i n g t e n d t o d i s p e n s e w it h a s t r o p h y s ic a l n e ut r i n o s i n f a v o u r laboratory in Tsukuba to the Super-Kamiokande detec- 2 associate editor. “atmospheric” splitting usually quantified by∆ m32 (see not know if the neutrino mixing matrix has imaginary of more controllable accelerator and reactor sources. The tor, 250 km away under Mount Ikeno on the other side of

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FEATURE NEUTRINOS FEATURE NEUTRINOS

from Fermilab to northern Minnesota from 2005 to 2012, Not super normal hierarchy inverted hierarchy

B Kayser made world-leading measurements of the parameters but hyper ν ν 3 2 describing the oscillation. A visualisation of

ν1 With νμ → ν τ o s c i l l at io n s e s t a bl i s h e d, t h e n e x t g e n e r at io n Hyper-Kamiokande the Hyper- of experiments innovated in search of a subtler effect. Kamiokande T2K (K2K’s successor, with the beam now originating at detector – a (mass)2 J-PARC in Tokai) and NOvA (which analyses oscillations 260,000 tonne over the longer baseline of 810 km between Fermilab and gadolinium-doped Ash River, Minnesota) both have far detectors offset by water-Cherenkov ν 2 a few degrees from the direction of the peak flux of the detector with a ν beams. This squeezes the phase space for the pion decays, fiducial volume 1 ν3 resulting in an almost mono-energetic flux of neutrinos. 8.4 times greater He re, a qu i r k of t he m i x i n g c on s pi re s t o m a ke t he mu s ic a l than its 2 2 [|U |2] νe [|Uei| ] νμ [|Uμi| ] ντ τi a n a lo g y o f a p a i r o f m e t a l lo p h o n e s p a r t ic u l a rl y s t r o n g: t o a predecessor. good approximation, the muon neutrinos ring out with two Excavation of 2 Little and large A narrow splitting between neutrino mass eigenstates, ∆m21, f r e q ue n c ie s o f r o u g h l y e q u a l a m pl it ud e, t o y ie ld a n a l m o s t the cavern has –5 2 2 is known to be about +7.4 × 10 eV , and a larger splitting, ∆m32, is known to be p e r fe c t d i s a p p e a r a n c e o f muo n n e ut r i n o s – a n d m a x i mu m already begun. approximately 2.5 × 10–3 eV 2 in magnitude, though its sign is unknown. The colours sensit iv it y to t he appearance of electron neut rinos. roughly indicate coupling to the charged leptons. Testing CP symmetry maximum sensitivity to Δm2 = 10 eV2 1 eV2 0.1 eV2 10–2 eV2 The three neutrino mass eigenstates mix to make electron, M Ray ner emulsion neutrino factory muon and tau neutrinos according to the Pontecorvo– plastic scintillator OPERA ICARUS Maki–Nakagawa–Sakata (PMNS) matrix, which describes –3 2 10 GeV water 10 eV MINOS+ three rotations and a complex phase δCP that can cause liquid argon charge–parity (CP) violation – a question of paramount δCP does not affect disappearance probabilities. By switch- The next generation liquid scintillator MINOS DUNE i m p or t a n c e i n t h e fie ld d ue t o it s r e le v a n c e t o t h e u n k now i n g t h e p ol a r it y o f t h e m a g n e t ic h or n, t h e e x p e r i m e nt s c a n Two long-baseline accelerator-neutrino experiments magnetised iron K2K NOvA 10–4 eV2 origin of the matter–antimatter asymmetry in the uni- compare t he probabilities for t he CP-mirror oscillations roughly an order of magnitude larger in cost and detector 1 GeV SBND MicroBooNE – – ICARUS verse (see p40). Whatever the value of the complex phase, νμ → νe and ν μ → ν e d i r e c t l y. NO vA d at a a r e i n c o n c lu s i v e at mass than T2K and NOvA have received green lights from SciBooNE MiniBooNE T2K ND280 leptonic CP violation can only be observed if all three of pr e s e nt. T 2 K d at a c u r r e nt l y e r r t o w a rd s n e a r m a x i m a l C P the Japanese and US governments: Hyper-Kamiokande

Hyper-Kamiokande the angles in the PMNS matrix are non-zero. Experiments violation in the vicinity of δCP = –π/2. The latest analysis, a n d DU N E. O n e o f t h e i r pr i m a r y m i s s io n s i s t o r e s ol v e t h e –5 2 with atmospheric and solar neutrinos demonstrated this published in April, disfavours leptonic CP conservation quest ion of leptonic CP v iolat ion. 100 MeV 10 eV

neutrino energy for two of the angles. At the beginning of the last decade, (δCP = 0, ±π) at 2σ significance for all possible mixing Hyper-Kamiokande will adopt the same approach as T2K,

KARMEN 2 LSND 32 short-baseline reactor-neutrino experiments in China parameter values (see p8). Statistical uncertainty is the but will benefit from major upgrades to the beam and the 2 2 JSNS Δm 21 (Daya Bay), Korea (RENO) and France (Double Chooz) were biggest limit ing factor. n e a r a n d f a r d e t e c t or s i n a d d it io n t o t h o s e c u r r e nt l y u n d e r- Δm accelerator in a race with T2K to establish if the third angle, which Major upgrades planned for T2K next year target sta- way in the present T2K upgrade. To improve the treatment of 10 MeV neutrinos reactor leads to a coupling between ν3 and electrons, was also tistical, interaction-model and detector uncertainties. systematic errors, the suite of near detectors will be comple- neutrinos non-zero. In the reactor experiments this would be seen A substantial increase in beam intensity will be accom- m e nt e d b y a n i n g e n io u s n e w g a d ol i n at e d w at e r- C h e r e n k o v PROSPECT DANSS Double Chooz SoLid NEOS Daya Bay KamLAND as a small deficit of electron antineutrinos a kilometre or panied by a new fine-grained scintillating target for the d e t e c t or at a n i nt e r m e d i at e b a s e l i ne: b y s p a n n i n g a r a n ge Neutrino-4 STEREO RENO 1 MeV JUNO s o f r o m t h e r e a c t or s; i n T 2 K t h e s m o k i n g g u n w o u ld b e t h e N D 2 80 n e a r-d e t e c t or c o m ple x, w h ic h w i l l lo w e r t h e e n e r g y of off-axis angles, it will drive down interaction-model appearance of a small number of electron neutrinos not t h r e s h old t o r e c o n s t r uc t t r a c k s. Ne w t r a n s v e r s e T P C s w i l l systematics by exploiting previously neglected informa- 1 m 10 m 100 m1 km 10 km 100 km 103 km 104 km present in t he init ial muon-neutrino-dominated beam. i m pr o v e N D 2 80’s a c c e p t a n c e at h i g h a n g le s, y ie ld i n g a b e t- tion on the how the flux varies as a function of the angle oscillation distance A f t e r d at a t a k i n g w a s c ut s h or t b y t h e g r e at S e n d a i e a r t h- ter cancellation of systematic errors with the far detector, relative to the centre of the beam. Hyper-Kamiokande’s Not natural Neutrino-oscillation experiments using neutrinos from nuclear q u a k e a n d t s u n a m i o f M a rc h 201 1, T 2 K p u bl i s h e d e v id e n c e Super-Kamiokande, which is being upgraded by loading increased statistical reach will also be impressive. The reactors or accelerator beams, as a function of the distance from source to detector for t h e a p p e a r a n c e o f s i x e le c t r o n-n e ut r i n o e v e nt s, o v e r t h e 0.01% g a d ol i n iu m s a lt s i nt o t h e o t h e r w i s e u lt r a p u r e w at e r. power of the Japan Proton Accelerator Research Complex and the peak energy of the neutrinos. Open markers indicate future projects expected background of 1.5 ± 0.3 i n t h e c a s e o f n o c o upl i n g. As in reactor-neutrino detectors, this will provide a tag (J-PARC) beam will be increased from its current value of (for detectors in excess of 5 kton, the area of the marker is proportional to the Alongside a single tau-neutrino candidate in OPERA, these for a nt i ne ut r i no e ve nt s, t o i mpro ve s a mple p u r it ie s i n t he 0.5 M W up t o 1.3 M W, a n d t h e n e w f a r d e t e c t or w i l l b e fi l le d detector mass) and italics indicate completed experiments. The experiments are were t he first neut rinos seen to appear in a detector w it h searc h for leptonic CP v iolat ion. w it h 260,000 t o n n e s o f u lt r a p u r e w at e r, y ie ld i n g a fid uc i a l coloured according to target material. The “magic-baseline” neutrino factory a n e w fl a v o u r, a s pr e v io u s s i g n a l s h a d a l w a y s r e g i s terda T 2 K a n d NO vA b o t h pl a n t o r o u g h l y d o u ble t h e i r c u r r e nt volume 8.4 times larger than that of Super-Kamiokande. proposed in the 2011 international design study is plotted for reference. deficit of an expected flavour. In the closing days of the year, data sets, and are working together on a joint fit, in a bid to P r o c u r e m e nt o f t h e p h o t o -mu lt i pl ie r t u b e s w i l l b e g i n t h i s Double Chooz published evidence for 4121 electron–anti- better understand correlations between systematic uncer- year, and the five-year-long excavation of the cavern has Ho n s hu. K 2 K c o n fi r m e d t h at muo n n e ut r i n o s “d i s a p p e a r” as ne ut r i no e ve nt s, u nd e r t he e x p e c te d t a l ly for no c oupl i n g tainties, and break degeneracies between measurements already begun. Data taking is scheduled to commence Muon a function of propagation distance over energy. The exper- of 4344 ± 165, reinforcing T2K’s 2.5σ i nd ic at ion. Day a B ay o f C P v iol at io n a n d t h e m a s s h ie r a rc h y. I f t h e C P-v iol at i n g in 2027. “The expected precision on δ is 10–20 degrees, CP neutrinos ring i m e nt s t o g e t h e r s up p or t e d t h e h y p o t h e s i s o f a n o s c i l l at io n a n d R E NO p ut t h e m at t e r t o b e d t h e fol lo w i n g s pr i n g, w it h phase is indeed maximal, as suggested by the recent T2K depending on its true value,” says Hyper-Kamiokande out with two to tau neutrinos, which could not be directly detected at 5σ e v id e n c e a pie c e t h at t h e ν3-electron coupling was indeed result, the experiments may be able to exclude CP con- international co-spokesperson Francesca di Lodovico of t h at e n e r g y. B y i n c r e a s i n g t h e b e a m e n e r g y w e l l a b o v e t h e non-zero. The key innovation for the reactor experiments servation with more than 99% confidence. “At this point King’s College, London. frequencies of t a u-le p t o n m a s s, t h e C E R N Ne ut r i n o s t o G r a n S a s s o (C NGS) was to minimise troublesome flux and interaction sys- we will be in a transition from a statistics-dominated to In the US, the Deep Underground Neutrino Ex periment roughly equal pr oj e c t, w h ic h r a n f r o m 2006 t o 201 2, c o n fi r m e d t h e o s cil- temat ics by also placing detectors close to t he reactors. a systematics-dominated result,” says T2K spokesperson (DUNE) will exploit the liquid-argon–TPC technology amplitude, l at io n t o t a u n e ut r i n o s b y d i r e c t l y o b s e r v i n g t a u l e p t o n s i n Since then, T2K and NOvA, which began taking data A t s u k o Ic h i k a w a o f t h e Un i v e r s it y o f Ky o t o. “It i s d i ffic u lt t o first deployed on a large scale by ICARUS – OPERA’s sister to yield t h e OPE R A d e t e c t or. M e a n w h i le, t h e M a i n I nj e c t or Ne ut r i n o in 2014, have been chasing leptonic CP violation – an say, but our sensitivity will likely be limited at this stage by detector in the CNGS project. The idea for the technology almost perfect Oscillation Search (MINOS), which sent muon neutrinos analysis that is out of the reach of reactor experiments, as a c o n v olut io n o f n e ut r i n o -i nt e r a c t io n a n d flu x s y s t e m at ic s.” d at e s b a c k t o 1977, w h e n C a rlo R u b bi a pr o p o s e d u s i n g l iq u id disappearance

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FEATURE NEUTRINOS FEATURE NEUTRINOS JUNO JUNO 2000 days of data taking 120 no oscillations only solar term normal hiearchy

V ISOSi m/R Ha ida r i a nd X Lu 100 inverted hierarchy

80

60 2 sin 2θ12

sin2 2θ 40 13 thousands of events per MeV

20 2 2 Δm32 Δm21 0 0123456789 – Eνe (MeV)

An oscillation within an oscillation Left: the evolution of the fraction of each flavour in the wavefunction of electron antineutrinos as they 2 traverse the 53 km from a nuclear reactor to the JUNO detector at three different energies. The fine oscillations due to∆ m32 are plotted coiling in the sense corresponding to the normal mass hierarchy. The evolution of a muon neutrino in the T2K experiment is plotted for reference. Right: JUNO plans to distinguish the mass hierarchy through exquisite energy resolution.

rather than gaseous argon as a drift medium for ionisa- t h i s d e c a d e. Wor k o n t h e n e a r-d e t e c t or s it e a n d t h e “PIP-II” will also encompass proton decay, high-precision meas- accelerator or atmospheric neutrinos,” says spokesperson Call to ordering tion electrons. Given liquid-argon’s higher density, such upgrade to Fermilab’s accelerator complex began last year. urements of solar neutrinos, supernova-relic neutrinos, Yifang Wang of the Chinese Academy of Sciences in Beijing. Excavation of the detectors can serve as both target and tracker, providing Though similar to Hyper-Kamiokande at first glance, d a r k-m at t e r s e a rc h e s, t h e p o s s i ble d e t e c t io n o f s ol a r-fl a r e “I n s i x y e a r s o f d at a t a k i n g, t h e s t at i s t ic a l s i g n i fic a n c e w i l l cavern for the high-resolution 3D images of the interactions – an inval- DU N E’s a p pr o a c h i s d i s t i n c t a n d c o m ple m e nt a r y. W it h b e a m neutrinos and neutrino geophysics.” be higher than 3σ.” JUNO experiment, uable tool for reducing systematics related to the murky e n e r g y a n d b a s e l i n e b o t h fo u r t i m e s g r e at e r, DU N E w i l l h a v e Half a century since Ray Davis and two co-authors JUNO has completed most of the digging of the under- a 20 kton world of neutrino–nucleus interactions. greater sensitivity to flavour-dependent coherent-forward- published evidence for a 60% deficit in the flux of solar ground laboratory, and equipment for the production and liquid-scintillator scattering with electrons in Earth’s crust – an effect that neutrinos compared to John Bahcall’s prediction, DUNE p u r i fic at io n o f l iq u id s c i nt i l l at or i s b e i n g f a br ic at e d. A toal detector located Spectacular performance modifies oscillation probabilities differently depending already boasts more than a thousand collaborators, and of 18,000 20-inch photomultiplier tubes and 26,000 3-inch 700 m beneath the The technology is currently being developed in two on the mass hierarchy. With the Fermilab beam directed Hyper-Kamiokande’s detector mass is set to be 500 times photomultiplier tubes have been delivered, and most of Dashi hill in prototype detectors at CERN. The first hones ICARUS’s straight at the detector rather than off-axis, a broader greater than Davis’s tank of liquid tetrachloroethylene. them have been tested and accepted, explains Wang. The Guangdong, single-phase approach. “The performance of the proto- r a n g e o f n e ut r i n o e n e r g ie s w i l l a l lo w DU N E t o o b s e r v e t h e If Ray Davis was the conductor who set the orchestra in i n s t a l l at io n o f t h e d e t e c t or i s s c h e d u le d t o b e g i n n e x t y e a r. China, is almost type has been absolutely spectacular, exceeding everyone’s oscillation pattern from the first to the second oscillation motion, then these large experiments fill out the massed JUNO will arguably be at the vanguard of a precision era for complete. e x p e c t at io n s,” s a y s DU N E c o -s p o k e s p e r s o n E d Bluc h e r o f m a x i mu m, a n d s i mu lt a n e o u s l y fit a l l b ut t h e s ol a r m i x ing ranks of the violin section, poised to deliver what may well the physics of neutrino oscillations, equipped to measure the t h e Un i v e r s it y o f C h ic a g o. “A f t e r a l m o s t t w o y e a r s o f o p e r- p a r a m e t e r s. A n d w it h d e t e c t or, flu x a n d i nt e r a c t io n u n cer- be the most stirring passage of the neutrino-oscillation m a s s s pl it t i n g s a n d t h e s ol a r m i x i n g p a r a m e t e r s t o b e t t e r at io n, w e a r e c o n fid e nt t h at t h e l iq u id–a r g o n t e c h n olo g y is tainties all distinct, a joint analysis of both experiments’ symphony. But other sections of the orchestra also have than 1% precision – an improvement of about one order ready to be deployed at t he huge scale of t he DUNE detec- data could break degeneracies and drive down systematics. important parts to play. of magnitude over previous results, and even better than tors.” In parallel, the second prototype is testing a newer “If CP violation is maximal and the experiments collect the quark sector, claims Wang, somewhat provocatively. dual-phase concept. In this design, ionisation charges data as anticipated, DUNE and Hyper-Kamiokande should Mass hierarchy “J U NO’s c a p a bi l it ie s for s up e r n o v a-b u r s t n e ut r i n o s, d i ff u s e d drift through an additional layer of gaseous argon before both approach 5σ significance for the exclusion of lep- The question of the neutrino mass hierarchy will soon supernova neutrinos and geoneutrinos are unprecedented, reaching the readout plane. The signal can be amplified tonic CP conservation in about five years,” estimates DUNE be addressed by the Jiangmen Underground Neutrino and it can be upgraded to be a world-best double-beta-decay here, potentially easing noise requirements for the read- c o -s p o k e s p e r s o n St e f a n S öld n e r-Re m b old o f t h e Un i v e r s it y O b s e r v at or y ( J U NO) e x p e r i m e nt, w h ic h i s c u r r e nt l y u n d e r detector once the mass hierarchy is measured.” out electronics, and increasing the maximum size of the of Manchester, noting that the experiments will also be construction in China. The project is an evolution of the With JUNO, Hyper-Kamiokande and DUNE now joining detector. The dual-phase prototype was filled with argon highly complementary for non-accelerator topics. The most Daya Bay experiment, and will seek to measure a deficit a growing ensemble of experiments, the unresolved leit- A rich in summer 2019 and is now recording tracks. striking example is supernova-burst neutrinos, he says, of electron antineutrinos 53 km from the Yangjiang and m o t i f s o f t h e t h r e e-n e ut r i n o p a r a d i g m m a y fi n d r e s olut io n The final detectors will have about twice the height and referring to a genre of neutrinos only observed once so far, Taishan nuclear-power plants. As the reactor neutrinos t h i s d e c a d e, or s o o n a f t e r. B ut t h e or y a n d e x p e r i m e nt b o t h programme of 10 to 20 times the footprint. Following the construction of during 15 seconds in 1987, when neutrinos from a supernova travel, the small kilometre-scale oscillation observed by hint, quite independently, that nature may have a scherzo short-baseline an initial single-phase unit, the DUNE collaboration will in the Large Magellanic Cloud passed through the Earth. Daya Bay will continue to undulate with the same wave- t w ist in store before t he g rand finale. experiments likely pick a mix of liquid-argon technologies to complete “While DUNE is primarily sensitive to electron neutrinos, length, revealed in JUNO as “fast” oscillations on a slower A rich programme of short-baseline e x p e r i m e nt s pr o m- promises their roster of four 10 kton far-detector modules, set to be Hyper-Kamiokande will be sensitive to electron antineu- and deeper first oscillation maximum due to the smaller ises to bolster or e xc lude e x per i ment a l h i nt s of a four t h to confirm 2 installed a kilometre underground at the Sanford Under- t r i n o s. T h e d i ffe r e n c e b e t w e e n t h e t i m i n g d i s t r i b ut io nsof solar mass splitting ∆m21 (see “An oscillation within an sterile neutrino with a relatively large mixing with the or exclude ground Research Laboratory in Lead, South Dakota. Site these samples encodes key information about the dynamics oscillation” figure). e le c t r o n n e ut r i n o t h at h a v e d o g g e d t h e fie ld s i n c e t h e l ate hints of a preparation and pre-excavation activities began in 2017, of the supernova explosion.” Hyper-Kamiokande spokes- “JUNO can determine the neutrino mass hierarchy in an 1990s. Four anomalies stack up as more or less consist- fourth sterile and full excavation work is expected to begin soon, with person Masato Shiozawa of ICRR Tokyo also emphasises unambiguous and definite way, independent from the CP ent among themselves. The first, which emerged in the neutrino the goal that data-taking begin during the second half of the broad scope of the physics programmes. “Our studies p h a s e a n d m at t e r e ffe c t s, u n l i k e o t h e r e x p e r i m e nt s u sing mid-1990s at Los Alamos’s Liquid Scintillator Neutrino

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FEATURE NEUTRINOS

T P C s – a b e s p o k e n e w s h or t-b a s e l i n e d e t e c t or (SBN D), t h e

Fermilab e x i s t i n g M ic r oB o oN E d e t e c t or, a n d t h e r e f u r bi s h e d IC A RUS detector – to resolve the LSND anomaly once and for all. SBN D i s c u r r e nt l y u n d e r c o n s t r uc t io n, M ic r oB o oN E i s o p e r- ational, and ICARUS, removed from its berth at Gran Sasso a n d s h i p p e d t o t h e US i n 2017, h a s b e e n i n s t a l l e d at Fe r m i l a b, fol lo w i n g w or k o n t h e d e t e c t or at C E R N. “T h e s h or t-b a s e l i n e neutrino programme at Fermilab has made tremendous technical progress in the past year,” says ICARUS spokes- person and Nobel laureate Carlo Rubbia, noting that the detector will be commissioned as soon as circumstances a l lo w, g i v e n t h e c or o n a v i r u s p a n d e m ic. “O n c e b o t h IC A RUS and SBND are in operation, it will take less than three years with the nominal beam intensity to settle the question of whether neutrinos have an even more mysterious character than we thought.” Outside of the pur view of oscillation experiments with artificially produced neutrinos, astrophysical observatories will scale a staggering energy range, from the PeV-scale neutrinos reported by IceCube at the South Pole, down, perhaps, to the few-hundred-μeV cosmic neutrino back- ground sought by experiments such as PTOLEMY in the US. Meanwhile, the KATRIN experiment in Germany is Discovery science - Magnet UHV chamber Sterile Detector (LSND), is an excess of electron antineutrinos z e r oi n g i n o n t h e e d g e s o f b e t a-d e c a y d i s t r i b ut io n s t o s e t a n suggestion that is potentially consistent with oscillations involving a a b s olut e s c a le for t h e m a s s o f t h e p e c u l i a r m i x t u r e o f m a s s In 2018 the sterile neutrino at a mass splitting ∆m2 ∼ 1 eV2. Two other eigenstates that make up an electron antineutrino (CERN MiniBooNE quite disparate anomalies since then – a few-percent Courier Ja nu a r y/ Fe br u a r y 2020 p2 8). A t t h e s a m e t i m e, a h o s t collaboration deficit in the expected flux from nuclear reactors, and a of experiments are searching for neutrinoless double-beta reported evidence deficit in the number of electron neutrinos from radio- decay – a process that can only occur if the neutrino is its for an excess active decays in liquid-gallium solar-neutrino detectors own antiparticle. Discovering such a Majorana nature for 381.2 ± 85.2 – c o u ld b e e x pl a i n e d i n t h e s a m e w a y. T h e fo u r t h a n o m a l y, the neutrino would turn the Standard Model on its head, electron–neutrino from Fermilab’s MiniBooNE experiment, which sought and offer grist for the mill of theorists seeking to explain events in their to replicate the LSND effect at a longer baseline and a t h e t i n i n e s s o f n e ut r i n o m a s s e s, b y b a l a n c i n g t h e m a g a i n s t detector higher energy, is the most recent: a sizeable excess of still-to-be-discovered heavy neutral leptons. (pictured), both electron neutrinos and antineutrinos, though at a compared to lo w e r e n e r g y t h a n e x p e c t e d. It’s i m p or t a nt t o n o t e, h o w- Indispensable input expected rates. e v e r, t h at e x p e r i m e nt s i n c lud i n g K A R M E N, M INOS+ a n d According to Mikhail Shaposhnikov of the Swiss Federal IceCube have reported null searches for sterile neutrinos Institute of Technology in Lausanne, current and future that fit the required description. Such a particle would reactor- and accelerator-neutrino experiments will provide also stand in tension with cosmology, notes phenome- a n i n d i s p e n s a ble i n p ut for u n d e r s t a n d i n g n e ut r i n o p h y s ic s. nologist Silvia Pascoli of Durham University, as models A n d n o t i n i s ol at io n. “To r e a c h a c o m ple t e pic t u r e, w e a l s o predict it would make too large a contribution to hot need to know the mechanism for neutrino-mass genera- dark matter in the universe today, unless non-standard tion and its energy scale, and the most important question scenarios are invoked. here is the scale of masses of new neutrino states: if lighter Three different types of experiment covering three than a few GeV, these particles can be searched for at new ord e r s o f m a g n it ud e i n b a s e l i n e a r e n o w s e e k i n g t o s e t t le experiments at the intensity frontier, such as SHiP, and at the sterile-neutrino question in the next decade. A smat- precision experiments looking for rare decays of mesons, tering of reactor-neutrino experiments a mere 10 metres or such as Belle II, LHCb and NA62, while the heavier states s o f r o m t h e s o u rc e w i l l d i r e c t l y pr o b e t h e r e a c t or a n o m a l y m a y b e a c c e s s i bl e at AT L A S a n d C M S, a n d at f ut u r e c i rc u l a r at ∆m2 ∼ 1 eV 2. The data reported so far are intriguing. colliders,” explains Shaposhnikov. “These new particles Korea’s NEOS experiment and Russia’s DANSS experiment can be the key in solving all the observational problems r e p or t s i r e n s i g n a l s b e t w e e n 1 a n d 2 eV2, a n d N EU T R INO -4, of the Standard Model, and require a consolidated effort a l s o b a s e d i n Ru s s i a, r e p or t s a s e e m i n g l y o ut l a n d i s h s i g- of neutrino experiments, accelerator-based experiments nal, indicative of very large mixing, at 7 eV2. In parallel, a n d c o s m ol o g ic a l o b s e r v at io n s. O f c o u r s e, it r e m a i n s t o b e J-PA RC’s JSNS 2 experiment is gearing up to try to reproduce seen if this dream scenario can indeed be realised in the the LSND effect using accelerator neutrinos at the same coming 20 years.”  Quality Production energy and baseline. Finally, Fermilab’s short-baseline prog ramme w il l t horoughly address a notable wea k ness Further reading o f b o t h L SN D a n d M i n i B o oN E: t h e l a c k o f a n e a r d e t e c t or. F Close 2012 Neutrino Ox ford Universit y Press. The Fermilab programme will combine three liquid-argon C Giunti and T Lasserre 2019 Ann. Rev. Nucl. Part. Sci. 69 163.

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FEATURE LEPTONIC CP VIOLATION FEATURE LEPTONIC CP VIOLATION

hypothesis that this violation arises from a single complex Fig. 1. All the 1.5 excluded at CL > 0.95 phase in the quark mixing matrix. This matrix gives the excluded area has CL > 0.95 experimental amplitude for any particular negatively-charged quark, γ constraints on the whether down, strange or bottom, to convert via a weak 1.0 quark-mixing Δmd & Δ ms THE SEARCH FOR interaction into any particular positively-charged quark, parameters be it up, charm or top. Just two parameters in the quark sin 2β relating to CP 0.5 mixing matrix, ρ and η, whose relative size determines the Δmd violation intersect α complex phase, account very successfully for numerous εK at a single point LEPTONIC CP VIOLATION γ β quark phenomena, including both CP-violating ones and 0.0 at the apex of α others. This is impressively demonstrated by a plot of all η– the black triangle. the experimental constraints on these two parameters |Vub| α (Reproduced –0.5 (fi g u r e 1). A l l t h e c o n s t r a i nt s i nt e r s e c t at a c o m m o npoint. from PDG Phys. Of course, precisely which (ρ, η) p oi nt i s c o n s i s t e nt w it h Rev. D 2018 98 all the data is not important. Lincoln Wolfenstein, who –1.0 εK 030001 p234)

created the quark-mixing-matrix parametrisation that γ sol. w/cos 2β < 0 includes and , was known to say: “Look, I invented (excl. at CL > 0.95) ρ η –1.5 ρ and η, and I don’t care what their values are, so why –1.0 –0.5 0.0 0.5 1.0 1.5 2.0 should you?” ρ– Having observed CP violation among quarks in numerous laboratory experiments of today, we might be tempted to think that we understand how CP violation in the early O ne r i ng t o fi nd t hem universe could have changed the world from one with equal μ+ e– An electron anti- quantities of matter and antimatter to one in which matter ν neutrino interacts in the dominates very heavily over antimatter. However, scenarios A detector Super-Kamiokande that tie early-universe CP violation to that seen among the π+ detector in Japan. quarks today, and do not add new physics to the Stand- Employing this detector ard Model of the elementary particles, yield too small a to compare CP–mirror– present-day matter–antimatter asymmetry. This leads one image oscillations, the μ– e+ to wonder whether early-universe CP violation involving ν (Dirac case) T2K experiment reported leptons, rather than quarks, might have led to the present B anti-detector a 95% confidence dominance of matter over antimatter. This possibility is π– ν (Majorana case) exclusion of leptonic envisaged by leptogenesis, a scenario in which heavy neutral CP invariance. leptons that were their own antiparticles lived briefly in the early universe, but then underwent CP-asymmetric decays, Fig. 2. The pursuit of leptonic CP violation is based on creating a world with unequal numbers of particles and comparing the rates for two CP-mirror-image processes. antiparticles. Such heavy neutral leptons are predicted by “see-saw” models, which explain the extreme lightness particles that are distinct from their antiparticles. How- of the known neutrinos in terms of the extreme heaviness ever, many theorists strongly suspect that neutrinos are of the postulated heavy neutral leptons. Leptogenesis can actually Majorana particles – that is, particles that are successfully account for the observed size of the present identical to their antiparticles. In that case, the tradi- matter–antimatter asymmetry. tional description of the search for leptonic CP violation The unknown origin of the matter–antimatter asymmetry observed is clearly inapplicable, since then the neutrinos and the Deniable plausibility antineutrinos are the same objects. However, the actual i n t he un iverse lo oms la rge i n t he sc ient i fic i mag i nat ion. In the straightforward version of this picture, the heavy experimental approach that is being pursued is a perfectly Boris Kayser explains how neutrino physicists are now closing in on a Super-Kamiokande neutral leptons are too massive to be observable at the valid probe of leptonic CP violation regardless of whether LHC or any foreseen collider. However, since leptogenesis neutrinos are of Dirac or of Majorana character. In fact, crucial piece of evidence in this most convoluted of detective stories. requires leptonic CP violation, observing this violation in this approach is completely insensitive to which of these the behaviour of the currently observed leptons would two possibilities nature has chosen. make it more plausible that leptogenesis was indeed the uckily for us, there is presently almost no antimatter cal systems whose behaviour changes if we replace every mechanism through which the present matter–antimatter Through a glass darkly in the universe. This makes it possible for us – made particle by its antiparticle, and interchange left and right. asymmetry of the universe arose. Needless to say, observing The pursuit of leptonic CP violation is based on compar- of matter – to live without being annihilated in In 1964, Cronin, Fitch and colleagues discovered that CP is leptonic CP violation would also reveal that the breaking of ing the rates for two CP mirror-image processes (figure L + matter–antimatter encounters. However, cosmology tells us indeed violated, in the decays of neutral kaons to pions – a CP symmetry, which before 1964 one might have imagined 2). In process A, the initial state is a π and an undis- that just after the cosmic Big Bang, the universe contained phenomenon that later became understood in terms of the to be an unbroken, fundamental symmetry of nature, is turbed detector. The final state consists of a μ+, an e–, equal amounts of matter and antimatter. Obviously, for behaviour of quarks. By now, we have observed quark CP not something special to the quarks, but is participated and a nucleus in the detector that has been struck by an Leptogenesis the universe to have evolved from that early state to the violation in the strange sector, the beauty sector and most in by all the constituents of matter. intermediate-state neutrino beam particle that travelled can account present one, which contains quite unequal amounts of recently in the charm sector (CERN Courier May/June 2019 To find out if leptons violate CP, we are searching for a long distance from its source to the detector. Since the for the matter and antimatter, the two must behave differently. p7). The observations of CP violation in B (beauty) meson THE AUTHOR what is traditionally described as a difference between neutrino was born together with a muon, but produced matter– This implies that the symmetry CP (charge conjugation decays have been particularly illuminating. Everything Boris Kayser the behaviour of neutrinos and that of antineutrinos. This an electron in the detector, and the probability for this antimatter × parity) must be violated. That is, there must be physi- we know about quark CP violation is consistent with the Fermilab. description is fine if neutrinos are Dirac particles – that is, to have happened oscillates as a function of the distance asymmetry

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FEATURE LEPTONIC CP VIOLATION FEATURE NEUTRON SCIENCE

Super NOvA NOvA collaboration A 14 kton stack of scintillating cells filled with mineral oil, the NOvA far detector, at Ash River, Minnesota, searches for neutrino oscillations using an accelerator beam created 810 km away at Fermilab, near Chicago.

the neutrino travels divided by its energy, the process As a result, while the quark mixing matrix is permitted is commonly referred to as muon–neutrino to electron– to contain just one complex phase, its leptonic analogue neutrino oscillation. may contain multiple complex phases that can contribute In process B, the initial and final states are the same as to CP violation in neutrino oscillations. in process A, but with every particle replaced by its anti- Leptonic CP violation is being sought by two current particle. In addition, owing to the character of the weak neutrino-oscillation experiments. The NOvA experiment interactions, the helicity (the projection of the spin along in the US has reported results that are consistent with An eye for structure The LADI instrument at the ILL, a quasi-Laue neutron diffractometer used for single-crystal studies of biological the momentum) of every fermion is reversed, so that left either the presence or absence of CP violation. The T2K macromolecules at high resolution. Neutron Laue diffraction patterns are recorded on a cylindrical detector, allowing the determination of protein and right are interchanged. Thus, regardless of whether experiment in Japan reports that the complete absence structures including the locations of hydrogen/deuterium atoms. (Credit: R Cubitt) neutrinos are identical to their antiparticles, processes A of CP violation is excluded at 95% confidence (see p8). and B are CP mirror images, so if their rates are unequal, Assuming that the leptonic mixing matrix is the same size CP invariance is violated. Moreover, since the probability as the quark one, so that it may contain only one complex of a neutrino oscillation involves the weak interactions of phase relevant to neutrino oscillations, the T2K data show leptons, but not those of quarks, this violation of CP invar- a preference for values of that phase, δ , that correspond to CP NEUTRON SOURCES JOIN THE iance must come from the weak interactions of leptons. near maximal CP violation. Of course, as Lincoln Wolfen-

Of course, we cannot employ an anti-detector in process stein would doubtless point out, the precise value of δCP is B in practice. However, the experiment can legitimately not important. What counts is the extremely interesting use the same detector in both processes. To do that, it experimental finding that the behaviour of leptons may FIGHT AGAINST COVID-19 must take into account the difference between the cross very well violate CP. In the future, the oscillation exper- sections for the beam particles in processes A and B to iments Hyper-Kamiokande in Japan and DUNE in the US Advanced neutron facilities such as the Institut Laue-Langevin are gearing up interact in this detector. Once that is done, the comparison will probe leptonic CP violation with greater sensitivity, of the rates for processes A and B remains a valid probe of and should be capable of observing it even if it should prove to enable a deeper understanding of the structural workings of SARS-CoV-2. CP non-invariance. to be fairly small (see p32). By searching for leptonic CP violation, we hope to find he global scientific community has mobilised at it ie s, t o d e t e r m i ne t he 3D s t r uc t u re s of prot e i n s of s e ve re The matrix reloaded out whether the breaking of CP symmetry occurs among an unprecedented rate in response to the COVID-19 acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Just as quark CP violation arises from a complex phase all the constituents of matter, including both the leptons T p a n d e m ic, b e yo n d ju s t p h a r m a c e ut ic a l a n d m e d ic a l which can lead to COVID-19 respiratory disease, and to in the quark mixing matrix, so leptonic CP violation in and the quarks, or whether it is a feature that is special researchers. The world’s most powerful analytical tools, identify potential drugs that can bind to these proteins in neutrino oscillation can arise from a complex phase, δ , in to the quarks. If leptonic CP violation should be defini- including neutron sources, harbour the unique ability to ord e r t o d i s a ble t h e v i r a l m a c h i n e r y. T h i s e ffor t h a s a l r e a dy T2K excludes CP the leptonic mixing matrix, which is the leptonic analogue tively shown to exist, this violation might be related to reveal the invisible, structural workings of the virus – delivered a large number of structures and increased our the complete of the quark mixing matrix. However, if, as suggested the reason that the universe contains matter, but almost w h ic h w i l l b e e s s e nt i a l t o d e v e lo pi n g e ffe c t i v e t r e at m e nt s. understanding of what potential drug candidates might THE AUTHORS absence of by several short-baseline oscillation experiments, there no antimatter, so that life is possible.  Since the outbreak of the pandemic, researchers worldwide look like in a remarkably short amount of time, with the leptonic Matthew exist not only the three well-established neutrinos, but have been using large-scale research infrastructures such number increasing eac h week. Blakeley and CP violation also additional so-called “sterile” neutrinos that do not Further reading as synchrotron X-ray radiation sources (CERN Courier M a y/ COVID-19 impacted the operation of all advanced neutron Helmut Schober at 95% participate in Standard Model weak interactions, then The NOvA Collaboration 2019 Phys. Rev. Lett. 123 151803. June 2020 p29), as well as cryogenic electron microscopy sources worldwide. With one exception (ANSTO in Australia, Institut Laue- confidence the leptonic mixing matrix is larger than the quark one. The T2K Collaboration 2020 Nature 580 339. (cryo-EM) and nuclear magnetic resonance (NMR) facil- which continued the production of radioisotopes) all of Langevin.

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FEATURE NEUTRON SCIENCE FEATURE NEUTRON SCIENCE M Blakeley/A Kovalevsky

Structural power ILL High flux Nick Woolridge/Biomedical Communications Woolridge/Biomedical Nick The ILL reactor, Determining the biological structures which typically that make up a virus such as SARS- operates four CoV-2 (pictured) allows scientists 50-day cycles per to see what they look like in three dimensions and to understand better year for user how they function, speeding up the experiments, design of more effective anti-viral provides the most drugs. Knowledge of the structures intense continuous highlights which parts are the neutron flux in the most important: for example, once world: 1.5 × 1015 researchers know what the active site neutrons per in an enzyme looks like, they can try second per cm2, to design drugs that fit well into the with a thermal active site – the classic “lock-and- power of 58.3 MW. key” analogy. This is also useful in the development of vaccines. Knowledge of are often made from weakened or the structural components that make killed forms of the microbe, its toxins, Neutron diffractionA neutron Laue diffraction pattern up a virus are important since vaccines or one of its surface proteins. from a crystal of HIV-1 protease in complex with a clinical inhibitor collected using the LADI instrument at ILL.

them were shut down in the context of national lockdowns Furthermore, in contrast to X-rays, which are scattered provides essential input into the long-term development tion. For example, the spike protein (S-protein) of SARS- aimed at reducing the spread of the disease. The neutron by electrons, neutrons are scattered by atomic nuclei, and of pharmaceuticals. This role will be further enhanced in CoV-2 that is responsible for mediating the attachment and community, however, lost no time in preparing for the so neutron-scattering lengths show no correlation with the context of advanced computer-aided drug development entry into human cells is of great relevance for developing resumption of activities. Some facilities like Oak Ridge the number of electrons, but rather depend on nuclear that will rely on an orchestrated combination of high- therapeutic defence strategies against the virus. Here, National Laboratory (ORNL) in the US have now restarted forces, which can even vary between different isotopes. power computing, artificial intelligence and broad-band neutron crystallography can potentially provide unique operation of their sources exclusively for COVID-19 studies. As such, while hydrogen (H) scatters X-rays very weakly, experimental data on structures. information about the specific domain of the S-protein Here in Europe, while waiting (impatiently) for the restart and protons (H+) do not scatter X-rays at all, with neutrons Neutron crystallography data add supplementary struc- where the virus binds to human cell receptors. Comparison of neutron facilities such as the Institut Laue-Langevin hydrogen scatters at a similar level to the other com- tural information to X-ray data by providing key details of the structure of this region between different varia- (ILL) in Grenoble, which is scheduled to be operational by mon elements (C, N, O, S, P) of biological macromolecules, regarding hydrogen atoms and protons, which are critical t io n s o f c or o n a v i r u s (S A R S- C oV-2 a n d S A R S- C oV ) o b t a i n e d mid-August, scientists have been actively pursuing SARS- allowing them to be located. Moreover, since hydrogen and players in the binding of such drugs to their target enzyme using X-rays suggests small alterations to the amino-acid CoV-2-related projects. Special research teams on the ILL its isotope deuterium (2H/D) exhibit different scattering through hydrogen bonding, and revealing important details s e q ue n c e m a y e n h a n c e t h e bi n d i n g a ffi n it y o f t h e S-pr o t ein site have been preparing for experiments using a range lengths and signs, this can be exploited in neutron studies of protein chemistry that help researchers decipher the to the human receptor hACE2, making SARS-CoV-2 more of neutron-scattering techniques including diffraction, t o e n h a n c e t h e v i s i bi l it y o f s p e c i fic s t r uc t u r a l fe at u r e s by exact enzyme catalytic pathway. In this way, neutron crys- infectious. Neutron studies will provide further insight small-angle neutron scattering, reflectometry and spec- substituting one isotope for the other. Examples of this tallography data can be hugely beneficial towards under- into this binding, which is crucial for the attachment of troscopy. Neutrons bring to the table what other probes include small-angle neutron scattering (SANS) studies of standing how these enzymes function and the design of the virus. These experiments are scheduled to take place, cannot, and are set to make an important contribution to macromolecular structures that provide low-resolution more effective medications to target them. For example, e.g. at ILL and ORNL (and possibly MLZ), as soon as large t he fight against SA RS-CoV-2. 3D information on molecular shape without the need for in the study of complexes between HIV-1 protease – the enough crystals have been grown. crystallization, and neutron-crystallography studies of enzyme responsible for maturation of virus particles into Unique characteristics proteins that provide high-resolution structures of pro- infectious HIV virions – and drug molecules, neutrons The big picture Discovered almost 90 years ago, the neutron has been teins, including the locations of individual hydrogen atoms can reveal hydrogen-bonding interactions that offer ways Biological systems have a hierarchy of structures: start- put to a multitude of uses to help researchers understand that have been exchanged for deuterium to make them to enhance drug-binding and reduce drug-resistance of ing from molecules that assemble into structures such as the structure and behaviour of condensed-matter. These particularly visible. Indeed, neutron crystallography can anti-retroviral therapies. proteins; these form complexes which, as supramolecular applications include a steadily growing number of investi- provide unique information on the chemistry occurring More than half of the SARS-CoV-2-related structures arrangements like membranes, are the building blocks of gations into biological systems. For the reasons explained within biological macromolecules, such as enzymes, as determined thus far are high-resolution X-ray structures of cells. These are of course the building blocks of our bodies. below, these investigations are complementary to the use recent studies on HIV-1 protease, an enzyme essential for the virus’s main protease, with the majority of these bound Every part of this huge machinery is subject to continu- of X-rays, NMR and cryo-EM. The necessary infrastruc- the life-cycle of the HIV virus, illustrate. to potential inhibitors. One of the main challenges for ous reorganisation. To understand the functioning, or in ture for neutron-scattering experiments is provided to performing neutron crystallography is that larger crystals the case of a disease, the malfunctioning of a biological the academic and industrial user communities by a global Treating and stopping COVID-19 are required than for comparable X-ray crystallography system, we therefore must get insight into the biological network of advanced neutron sources. Leading European Proteases are like biological scissors that cleave polypep- studies, owing to the lower flux of neutron beams relative mec hanism on all of t hese different leng t h scales. neutron facilities include the ILL in Grenoble, France, tide chains – the primary structure of proteins – at pre- to X-ray beam intensities. Nevertheless, given the ben- When it comes to studying the function of larger MLZ in Garching, Germany, ISIS in Didcot, UK, and PSI in cise locations. If the cleavage is inhibited, for example, by efits provided by the visualisation of hydrogen-bonding biological complexes such as assembled viruses, SANS Villigen, Switzerland. The new European flagship neutron appropriate anti-viral drugs, then so-called poly-proteins networks for understanding drug-binding, scientists have becomes an important analytical tool. The technique’s source – the European Spallation Source (ESS) – is under remain in their original state and the machinery of virus been optimising crystallisation conditions for the growth capacity to distinguish specific regions (RNA, proteins construction in Lund, Sweden. replication is blocked. For the treatment to be efficient this of larger crystals, in combination with the production of and lipids) of the virus – thanks to advanced deuteration Neutrons can Neutrons are a particularly powerful tool for the study inhibition has to be robust—that is, the drug occupying the fully deuterated protein in preparation for neutron crys- methods – enables researchers to map out the arrange- penetrate deep of biological macromolecules in solutions, crystals and active site should be strongly bound, ideally to atoms in the tallography experiments in the near future. Currently, ment of the various components, contributing invaluable into matter partially ordered systems. Their neutrality means neutrons main chain of the protease. This will increase the likeli- teams at ORNL, ILL and the DEMAX facility in Sweden are information to structural studies of SARS-CoV-2. While without can penetrate deep into matter without damaging the h o o d t h at t r e at m e nt s a r e e ffe c t i v e i n t h e lo n g r u n, d e s pite growing crystals for SARS-CoV-2 investigations. other analytical techniques provide the detailed atomic- damaging the samples, so that experiments can be performed at room mutations of the enzyme, since mutations occur only within Proteases are, however, not the only proteins where resolution structure of small biological assemblies, neutron samples temperature, much closer to physiological temperatures. the side chains of the enzyme. Neutron research, therefore, neutron crystallography can provide essential informa- scattering allows researchers to pan back to see the larger

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CCJulAug20_NEUTRON_v5.indd 44 24/06/2020 12:45 CCJulAug20_NEUTRON_v5.indd 45 24/06/2020 12:46 CERNCOURIER www. V o l u m e 6 0 N u m b e r 4 J u l y /A u g u s t 2 0 2 0 CERNCOURIER.COM CERNCOURIER.COM FEATURE NEUTRON SCIENCE OPINION pic t ure of f ul l molec ula r comple xes, at lower resolut ion. to be responsible for binding with the receptor of the host Ne ut r o n s c at t e r i n g i s a l s o u n iq ue l y s u it e d t o d e t e r m i n i n g cell. Defi ning this mechanism, which is decisive for the VIEWPOINT t he st r uc t ure of f unc t iona l membr ane proteins in phys- infection, will be essential to controlling the virus and its iological conditions. Neutron scattering will therefore potent ial future mutat ions in t he long ter m. ma ke it p ossible to map out t he st r uc t ure of t he comple x for med by t he S-protein and t he h ACE2 receptor. Tool of choice L a s t b ut n o t le a s t, a f u l l u n d e r s t a n d i n g o f t h e v i r u s’s l i fe A n d w e s h o u ld n o t for g e t t h at v i r u s e s i n t h e i r p h y s iolo g- c yc le r e q u i r e s t h e s t ud y o f t h e i nt e r a c t io n o f t h e v i r u s w it h ical environments are highly dynamic systems. Knowing t h e c e l l m e m br a n e, a n d t h e m e c h a n i s m it u s e s t o p e n e t r at e h o w t h e y m o v e, d e for m a n d c lu s t e r i s e s s e nt i a l for o p t i- A price worth paying t h e h o s t c e l l. S A R S- C oV-2 i s a v i r u s, l i k e HI V, t h at p o s s e s s e s mising diagnostic and therapeutic treatments. Neutron a viral envelope composed of lipids, proteins and sugars. spectroscopy, which is ideally suited to follow the motion Large research infrastructures are O-201906-179-2 T N-PHO CER By providing information on its molecular structure and of matter from small chemical groups to large macro- composition, the technique of neutron refl ectometry – molecular assemblies, is the tool of choice to provide essential drivers of economic progress, and w h e r e b y h i g h l y c ol l i m at e d n e ut r o n s a r e i n c id e nt o n a fl at t his infor mat ion. particle physicists have a duty to make this surface and the intensity of refl ected radiation is measured The League of Advanced European Neutron Sources (CERN message loud and clear, argues Rolf Heuer. as a function of angle or neutron wavelength – helps to Courier M a y/ Ju n e 2020 p49) h a s r a pid l y m o bi l i s e d t o c o n d uc t e luc id at e t h e pr e c i s e m e c h a n i s m t h e v i r u s u s e s t o p e n e t r at e all relev ant ex periments. We are equally in close contact Science, from the immutable logic of its Neutron the cell. Like in the case of SANS, the strength of neutron w it h o u r i nt e r n at io n a l p a r t n e r s, s o m e o f w h o m h a v e, or a r e mathematical underpinnings to the more scattering is r e fl e c t o m e t r y r e l ie s o n t h e f a c t t h at it pr o v id e s a d i ff ernt just in the process of, reopening their facilities. Scientists Brice/CERN M fluid realms of the social sciences, has also uniquely c o nt r a s t t o X-r a y s, a n d t h at t h i s c o nt r a s t c a n b e v a r ie d v i a have to make sure that each research subject is provided carried us from our humble origins to an suited to d e ut e r at io n a l lo w i n g, for e x a m ple, t o d i s t i n g u i s h a pr o t e i n w it h t h e b e s t-s u it e d a n a l y t ic a l t o ol – i n o t h e r w ord s, t h o s e understanding of such esoteric notions as gravitation and quantum mechanics. This determining inserted into the membrane from the membrane itself. that have the samples will be given the necessary beam knowledge has been applied to develop the structure Regarding SARS-CoV-2, this implies that neutron refl ec- time. Neutron facilities are fast-adapting with special devices such as GPS trackers and smart- of functional t o m e t r y c a n i n f a c t pr o v id e d e t a i le d s t r uc t u r a l i n for m at io n access channels to beam time having been implemented phones – a story repeated in countless Deep impact Projects such as the LHC deliver global visibility and impact. membrane on the interaction of small protein fragments, so-called t o a l lo w t h e s c ie nt i fi c c o m mu n it y t o r e s p o n d w it h o ut d elay Rolf-Dieter Heuer domains for a century or more – and it proteins peptides, that mimic the S-protein and that are believed to the challenge posed by COVID-19.  was CERN has delivered new tools for basic research T h e b e n e fit s o f Bi g S c i e n c e for e c o n o mic turnover and 12% of overall employment Director-General along the way in a virtuous circle. prosperity become more pertinent if we in Europe – represen ting a net annual from 2009 to 2015. While it is undeniable that science has consider the cumulative contributions to contribution of at least €1.45 trillion, and led us to a better world than that inhabited the 21st-century knowledge economy, topping contributions from the financial by our ancestors, and that it will continue which relies heavily on research and services and retail sectors (CERN Courier to deliver intellectual, utilitarian and innovation. In 2018, more than 40% of January/February 2020 p9). economic progress, advancement is not the CERN budget was returned to industry Of course, there are some who feel that always linear. Research has led us up blind in its member-state countries through limited resources for science should be PPoowweerriinngg yyoouurr AAcccceelleerraattoorr RReeaall TTiimmee CCoonnttrrooll SSyysstteemmss alleys, and taken wrong turnings, yet its the procurement of supplies and services, deployed in areas such as addressing strength is its ability to process data, to generating corollary benefits such as climate change, rather than blue-sky self-correct and to form choices based on o p e n i n g n e w m a r k e t s. I n c r e a s i n g e ffor t s, research. These views can be persuasive, the best available evidence. The current for example by the European Commis- but are misleading. Fundamental research RRDDCC__11447700 coronavirus pandemic could prove to be a sion, to require research infrastructures is every bit as important as directed great educator in the methods of science, to estimate their socioeconomic impact research, and through the virtuous circle demonstrating how the right course of are a welcome opportunity to quantify of science, they are mutually dependent. MTCA.4 Downconverter action evolves as the evidence accumu- and demonstrate our impact. The open questions and mind-bending lates. We’ve seen all too clearly how badly CERN has been subject to economic concepts explored by particle physics and things can go wrong when individuals and impact assessments since the 1970s, astronomy also serve to draw bright young MTCA.4 µRTM companiion for IFC_1420 AMC governments fail to grasp the importance with one recent cost–benefit analysis of minds into science, even if individuals 4 x RF SMA Inputs of evidence-based decision making. the LHC, conducted by economists at the go on to work in other areas. Surveys of Fundamental science has to make its University of Milan, concluding with 92% the career paths taken by PhD students Diirect to ADC (AC couplled): 10 dBm FS, 1 to 400 MHz case not only on the basis of cultural probability that benefits exceed costs, working on CERN experiments fully bear Hiigh dynamiic range to ADC: -50 to 20 dBm FS, 10 to 400 MHz wealth, but also in terms of socioeconomic even when attaching the very conservative this out (CERN Courier April 2019 p55). Down converter: -50 to 20 dBm FS, 10 to 1500 MHz benefit. In particle physics, we also have figure of zero to the value of the organisa- I n A pr i l 2020, a s a c u r t a i n-r a i s e r t o t h e 1 x RF SMA Output no shortage of examples. These go well tion’s scientific discoveries. More recent update of the European Strategy for Par- Diirect hiigh-speed DAC output beyond the web, although an economic studies (CERN Courier September 2018 ticle Physics, Nature Physics published a Vector modullator output: -20 to 10 dBm FS, 10 to 1500 MHz impact assessment of that particular p51) by the Milan group, focusing on the series of articles about potential future i n v e nt io n i s o n e t h a t I w o u l d b e v e r y i nt e r- High-Luminosity LHC, revealed a quan- directions for CERN. An editorial pointed 3 x MMCX diigiitall triiggers and 1 x MMCX GPIO ested in seeing. As of 2014, there were some t i fi a bl e r e t u r n t o s o c i e t y w e l l i n e x c esof out the strong scientific and utilitarian Desiigned for 2 x sllow MMCX anallog outputs 42,200 particle accelerators worldwide, the project’s costs, again, not including case for future colliders, concluding that: Hiighlly confiigurablle (diifferentiiall fiillter pllug-iins) 64% of which were used in industry, a it s s c i e nt i fic o ut p ut. E x t r a p ol a t i n g t h e se “Even if the associated price tag may seem LLRF & BPM Fundamental third for medical purposes and just 3% results, the authors show that future high – roughly as high as that of the Tokyo LLRF BPM DESY A1-complliiant µRTM for anallog siignalls research is in research – not bad for a technology colliders at CERN would bring similar Olympic Games – it is one worth paying.” every bit as invented for fundamental exploration. It’s s o c ie t a l b e n e fit s o n a n e v e n bi g g e r s c ale. This is precisely the kind of argument that a similar story for techniques developed Across physics more broadly, a 2019 we as a community should be prepared important To know more about our MTCA.4 product lliine, contact IOxOS Technollogiies ([email protected]) for particle detection, which have found report commissioned by the European to make if we are to ensure continuing as directed their way into numerous applications, Physical Society found that physics-based exploration of fundamental physics in the research especially in medicine and biology. industries generate more than 16% of total 21st century and beyond.

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CCJulAug20_Viewpoint_v3.indd 47 24/06/2020 11:56 CERNCOURIER www. V o l u m e 6 0 N u m b e r 4 J u l y /A u g u s t 2 0 2 0 CERNCOURIER.COM CERNCOURIER.COM OPINION OPINION INTERVIEW rie ranCRN n/CER Orda J ice, Br M exchanges between the atmosphere, INTERVIEW the oceans, the biosphere, the cryosphere … and the influence of human beings. The models involve many parameters that are poorly understood, so modellers have to ma ke plausible yet uncer tain c hoices. As a result, there is much more Lofty thinking fle x ibilit y in climate models, whereas there is almost none in the SM. Unfortunately, this flexibility means CERN’s Cosmics Leaving Outdoor Droplets (CLOUD) experiment has merged the best of t hat t he predict ive power of suc h particle physics and atmospheric science into a novel experimental approach. Spokesperson models is much weaker than it is in particle physics. Jasper Kirkby argues that this interdisciplinarity could benefit climate modelling, too. There are sk ills suc h as t he handling of data, stat ist ics and sof t w are opt imisat ion where J Kirkby Kirkby J What, in a nutshell, is CLOUD? Do you consider yourself a particle par t icle physics is probably t he It’s basically a cloud chamber, but not physicist or an atmospheric scientist? leading science in t he world, so I a conventional one as used in particle An experimental physicist! My would love to see CERN sponsor a physics. We realistically simulate training and my love is particle workshop where t he t wo communit ies selected atmospheric environments physics, but judging by the papers could e xc hange ideas and perhaps in an ultraclean chamber and study I write and review, I am now an even beg in to collaborate. This is the formation of aerosol particles atmospheric scientist. It was not what CLOUD has done. It’s polit ically On cloud nine Kirkby on the roof of the CLOUD detector in CERN’s East Hall back in 2018. from trace vapours, and how they difficult to make this transition. cor rect to tal k about t he power of grow to become the seeds for It was a case of going back to interdisciplinar y researc h, but it’s of cosmic rays on the process under are capable of producing abundant cloud droplets. We can precisely my undergraduate physics and very difficult in practical terms – study. A third major focus concerns particles and thus cloud seeds. Prior control all the conditions found high-school chemistry and learning especially when it comes to f unding the formation of smog under polluted to that it was thought that sulphuric throughout the atmosphere such as on the job. It’s also very rewarding. We because e x periments of ten fall into urban conditions. acid was essential to form aerosol gas concentrations, temperature, do experiments, like we all do at CERN, t he crac ks bet ween f unding agencies. par t icles. Since sulphuric acid w as ultraviolet illumination and “cosmic on a 24/7 basis, but with CLOUD I can What have CLOUD’s biggest five times lower in the pre-industrial ray” intensity with a beam from calculate things in my notebook and How has CLOUD’s focus evolved contributions been? atmosphere, climate models assumed CERN’s Proton Synchrotron (PS). The see the science that we are doing, so we during a decade of running? We have made several major that clouds were fewer and thinner aerosol processes we study in CLOUD know immediately what the new stuff CLOUD w as desig ned to e x plore discoveries and it’s hard to rank them. bac k t hen. This is impor tant because are poorly known yet climatically is and we can adapt our experiments whet her v ariat ions of cosmic rays Our latest result (p10) on the role of the pre-industrial era is the baseline important because they create the continuously during our run. in t he atmosphere affect clouds and ammonia and nitric acid in urban aerosol state from which we assess seeds for more than 50% of global On the other hand, in particle climate, and t hat’s st ill a major environments is very important for ant hropogenic impacts. The fact cloud droplets. physics the detectors are running all goal. What I didn’t realise at t he human healt h. We have found t hat that biogenic vapours make lots of We have 22 institutes and the the time but we really don’t know what beginning is how important ammonia and nit ric acid can drive t he aerosols and cloud droplets reduces crème de la crème of European and US is in the data without years of very aerosol–par t icle for mat ion is for growth rates of newly formed particles the contrast in cloud coverage (and atmospheric and aerosol scientists. Interdisciplinary Jasper Kirkby at his home in May 2020. careful analysis afterwards, so there climate and health, and just how up to more than 100 times faster t hus t he amount of cooling offset) It’s a fabulous mixture of physicists is this decoupling of the result from muc h is not yet understood. The than seen before, but only in short bet ween t hen and now. The for mat ion and chemists, and the skills we’ve ray–cloud link at CERN with an the actual measurement. Also, in largest uncer taint y facing predict ions spurts that have previously escaped rate of t hese pure biogenic par t icles learned from particle physics in terms experiment I named CLOUD. I did not CLOUD we don’t need a separate of global w ar ming is not due to a lac k detect ion. This can e x plain t he is enhanced by up to a factor 100 by of cooperating and pooling resources want to ride into another field telling discipline to tell us about the of understanding about g reen house puzzling observation of bursts of new galactic cosmic rays, so the pristine have been incredibly important for t hose g uys how to do t heir st uff, so I underlying theory or beauty of what we g ases, but about how muc h aerosols particles that form and grow under pre-indust rial at mosphere w as more the success of CLOUD. It’s the CERN wrote a note of my ideas and started are doing. In CLOUD you’re the theorist and clouds have increased since highly polluted urban conditions, sensitive to cosmic rays than today’s model, the CERN culture that we’ve to make contact with the atmospheric and the experimentalist at the same pre-indust rial t imes from human producing winter smog episodes. An polluted atmosphere. conveyed to another discipline. We community in Europe and build time – like it was in the early days of act iv it ies. Aerosol c hanges have earlier CLOUD result, also in Nature, There was an important result the implemented the best of CERN’s support from lab directors in particle particle physics. offset some of t he w ar ming from showed that a few parts-per-trillion of ver y first week we t ur ned on CLOUD, know-how in ultra-clean materials physics. I managed to assemble a g reen house g ases but we don’t amine vapours lead to extremely rapid when we saw t hat sulphuric acid does and built the cleanest atmospheric dream team to propose the experiment How would you compare the k now by how muc h – it could have formation of sulphuric acid particles, not nucleate on its own but requires chamber in the world. to CERN. The hard part was convincing Standard Model to state-of-the-art offset almost not hing, or as muc h limited only by the kinetic collision ammonia. Before CLOUD started, CERN that they should do this crazy climate models? as one hal f of t he w ar ming effect. rate. We had a huge fight w it h one of people were measuring particles How did CLOUD get off the ground? experiment. We proposed it in 2000 It’s night and day. The Standard Consequent ly, when we project the referees of this paper, who claimed but t hey weren’t able to measure t he In CLOUD The idea came to me in 1997 during and it was finally approved in 2006, Model (SM) is such a well formed for w ards, we don’t k now how muc h that it couldn’t be atmospherically molecular composition, so many a lecture at CERN given by Nigel which I think is a record for CERN to you’r e t he theory and remarkably high-quality Ear t h w ill w ar m later t his cent ur y to Many of our impor tant because no-one had experiments were being fooled by Calder, a former editor of New Scientist approve an experiment. There were theorist and the quantitatively that we can see bet ter t han a factor of t hree. experiments previously observed it. Finally, a paper unknown contaminants. magazine, who pointed out a new some people in the climate community experimentalist incredibly subtle signals in detectors Many of our experiments are are now aimed appeared in Science last year show ing result from satellite data about who were against the idea that cosmic against a background of something now aimed at reducing the aerosol that sulphuric acid–amine nucleation Have CLOUD results impacted at t he s a me at reducing possible links between cosmic rays rays could influence clouds. But we that is extremely well understood. uncertainties in anthropogenic climate policy? t i me – l i k e it is t he key process driv ing new par t icle and cloud formation. That Christmas, persevered and, once approved, things Climate models, on the other hand, climate change. Since all CLOUD the aerosol formation in Chinese megacities. The global climate models t hat was in the while we visited relatives in Paris, I went very fast. We started taking data are trying to simulate a very complex experiments are performed under uncertainties in A big result from the point of view inform the Intergovernmental Panel read a lot of related papers and came in 2009 and have been in discovery e a rly d ay s of system about what’s happening on different ionisation conditions, we anthropogenic of climate change came in 2016 on Climate Change (IPCC) have up with the idea to test the cosmic mode ever since. particle physics Earth’s surface, involving energy are also able to quant i f y t he effect climate change when we showed t hat t rees alone beg un to incor porate CLOUD aerosol

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CCJulAug20_Interview_v4.indd 48 24/06/2020 13:45 CCJulAug20_Interview_v4.indd 49 24/06/2020 13:46 CERNCOURIER www. V o l u m e 6 0 N u m b e r 4 J u l y /A u g u s t 2 0 2 0 CERNCOURIER.COM CERNCOURIER.COM OPINION INERVIEW OPINION parameterisations, and they are chamber itself is pretty much the Oceans cover two thirds of Earth’s impacting estimates of Earth’s climate only item that is untouched. When the surface and their latent heat of REVIEWS sensitivity. The IPCC assessments East Area is rebuilt there will be a new vaporisation is a huge stabiliser of are hugely impressive works of the beamline and a new experimental climate – they have never evaporated highest scientifi c quality. Yet, there zone for CLOUD. We think we have a nor completely frozen over. Also,

is something of a disconnect between 10-year programme ahead to address only around 2 of CO2 is in the what climate modellers do and t he quest ions we w ant to and to atmosphere and most of the rest is what we do in the experimental and settle the cosmic ray–cloud–climate dissolved in the oceans, so eventually, observational world. The modellers question. That will take me up to just over the course of several centuries, Fiction, in theory tend to work in national centres and over 80 years old CO2 in t he atmosphere w ill equilibrate connect with experiments through at near pre-industrial levels. The the latter’s publications, at the end Will humanity succee in reenting current warming is an important O-202002-036-2 T N-PHO zog/CER t Her SJ human. Highs and lows, loves and laughs, of the chain. I would like to see much catastrohic climate change change – and some argue it could Big Bang kindnesses and hurts, even tragedies, all closer linkage between the models I am an optimist, so I believe there produce a climate tipping point – By Irène Jacob play a part. Irène Jacob’s fictionalised and the measurements, as we do is always a way out of everything. but Earth has gone through larger family suffers much, yet although Irène Éditions Albin Michel (in French) in particle physics where there is a It’s very understandable that people changes in the past and life has holds nothing back, Big Bang is essentially fl uid connection between theory, want to freeze the exact temperature continued. So we should not be too an opt imist ic, li fe-affir ming tale. experiment and modelling. We do of Earth as it is now because we don’t pessimistic about Earth’s future. French actor Irène Jacob rose to inter- Science makes repeated cameo this already in CLOUD, where we have w ant to see a fl ood or deser t in our A nd we shouldn’t confl ate pollut ion national acclaim for her role in the 1991 appearances. There’s a passage in which several institutes who are primarily back garden. But I’m afraid that’s and climate change. Reducing filmThe Double Life of Véronique. She is the René is driving home from hospital after working on regional and global not how Earth is, even without the pollution is an absolute no brainer, but daughter of Maurice Jacob (1933–2007), w e lc o m i n g h i s fi r s t c h i l d i nt o t h e w orl d. aerosol-cloud models. ant hropogenic infl uence. Ear t h has environmental pollution is a separate a French theoretical physicist and head Distracted by emotion, he’s struck by a gone through much larger natural issue from climate change and should of CERN’s theory division from 1982 to great insight and has to pull over and Whats net on ODs horion climate oscillations, even on the be treated as such. 1988. Her new novel, Big Bang, is a fic- tell someone. How often does that hap- The East Hall at the PS is being recent timescale of homo sapiens. tionalised account of the daughter of a pen in the creative process? Biochemist completely rebuilt during CERN’s That being said, I think Earth’s Interie b Paola ataano and renowned physicist coming to terms with Kary Mullis tells a similar story in his current long shutdown, but the CLOUD climate is fundamentally stable. atthe halmers CERN. the death of her father and the arrival of memoirs. In his case, the idea for pol- her second child. Keen to demonstrate ymerase chain reaction came to him at the artistic beauty of science, she is also the end of hot May day on Highway 128 a patron of the Physics of the Universe with his girlfriend asleep next to him Endowment Fund established in Paris in the passenger seat of his little silver by George Smoot. Honda. Mullis got the Nobel prize. Both When Irène Jacob recites from her had a profound impact on t heir fields book, it is more than a reading, it’s a Alice in Wonderland is a charmingly performance. That much is not sur- recurrent theme, particularly the Chesh- prising: she is after all the much-feted ire cat. Very often, a passage ends with a c t or i n t h e s u b t l y r e fle c t i v e 1990 s fi l ms nothing left but an enigmatic smile, a of Krzysztof Kieślowski. What did come metaphor for life in the quantum world, PROVIDING as a surprise to this reader is just how where believing in six impossible things beautifully she writes. With an easy grace before breakfast is almost a prerequisite. CUTTING-EDGE SOLUTIONS a n d flu i d it y, s h e w e a v e s t o g e t h e r t h r eads Big Bang is not a page turner. Instead, of her life, of life in general, and of the each chapter is a beautifully formed FOR A PRECISELY KNOWN, vast mysteries of the universe vignette of family life. Take, for exam- Billed as a novel, Big Bang comes across Double life Irène Jacob reads an excerpt from Big Bang. ple, the passage that begins with a quote STABLE AND RELIABLE BEAM. more as a memoir, and that’s no acci- from Niels Bohr taken from René’s man- dent. The author’s aim was to use her this together, seen from the point in uscript, Des Quarks et des Hommes (pub- entourage, somewhat disguised, to tell a space–time at which Irène has to rec- lished as Au Coeur de la Matière). Bohr can universal story of the human condition. oncile her father’s passing with her own be paraphrased as saying: the opposite Names are changed, Irène’s well-known impending motherhood. of a profound truth is another profound physicist father becoming René, for For those who remember the CERN truth. As the passage moves on, it plays BEAM DIAGNOSTICS example, one of his middle names. The of the 1980s, the story begins with an with this theme, ending with the con- true chronology of events is not strictly opportunity to rediscover old friends clusion: if my story does not stand up, it’s LLRF CONTROLS observed, and maybe there’s some inven- and places. For those not familiar with because reality is very small. And if my tion, but behind the storytelling there pa r t ic le physics, it offers a g l i mpse i nto story is very small, it is because reality RF GENERATION & DISTRIBUTION is nevertheless a touching portrait of the field, to those who devote their lives does not stand up. a very real family. The backdrop to the to it, and to those who share their lives Whatever the author’s wish, Big Bang RF DIGITIZERS & CURRENT METERS o p e n i n g s c e n e s i s C E R N, m or e s p e c i fic a l l y with them. The initial chapters open the comes across as an admirably honest the corridors of the theory division in door to Irène Jacob’s world, just a crack. family portrait, at times uncomfortably the 1970s and 1980s, a regular stomping The atmosphere soon changes, though, so. It’s a portrait that goes much deeper ground for the young Irène. The reader as she flings the door wide open. More than the silver screen or the hallowed discovers the wonders of physics through than once I found myself wondering halls of academia. The cast of Big Bang the wide-open eyes of a seven-year-old whether I had the right to be there: is a very human family, and one that this child. Later on, that child-become-adult inside Irène Jacob’s life, dreams and reader came to like very much. Instrumentation Technologies, d.o.o. / Velika pot 22, SI-5250 Solkan, Slovenia / e: [email protected] / w: www.i-tech.si reflects on other wonders – those related nightmares. It is a remarkably intimate to the circle of life. The book ties all account, looking deep into what it is to be James Gillies CERN.

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New Perspectives on Einstein’s E = mc2 new perspectives on an equation such as chapters, which are more mathemati- E = mc2. The book’s true aim is to convey cal and draw heavily on publications by CAREERS Young Suh Kim and Marilyn E Noz to a broader audience the formal work the authors – a well-established writing World Scientific done by the authors on group theory. team who have co-authored many papers Therefore, a better-suited title may have relating to group theory. The initial part New Perspectives on Einstein’s E = mc2 mixes been “Group theoretical perspectives is easy to read and includes entertaining historical notes with theoretical aspects on relativity”, or even, more poetically, stories, such as Einstein’s mistakes when of the Lorentz group that impact rela- “When Wigner met Einstein”. filing his US tax declaration. Einstein, tivity and quantum mechanics. The title The first third of the book is an essay according to this story, was calculating Surveying the surveyors is a little perplexing, however, as one on Einstein’s life, with historical notes his taxes erroneously, but the US tax-

can hardly expect nowadays to discover on topics discussed in the subsequent payer agency was kind enough not to raise J-F Fuchs the issue. The reader has to be warned, The ne e d at CER N to a l ig n however, that the authors, professors at components within a fraction t h e Un i v e r s it y o f M a r y l a n d a n d Ne w Yor k of a millimetre demands Un i v e r s it y, h a v e a t e n d e n c y t o m a k e q u e s- tionable statements about certain aspects skills and tools beyond the of the development of physics that may scop e of nor m a l su r ve yor jobs. not be backed up by the relevant liter- ature, and may even contradict known facts. They have a repeated tendency to A career as a surveyor offers the best of two interpret the development of physical worlds, thinks Dominique Missiaen, a senior theories in terms of a Hegelian synthesis member of CERN’s survey, mechatronics and of a thesis and an antithesis, without any measurements (SMM) group: “I wanted to be a cited sources in support, which seems, in surveyor because I felt I would like to be inside most cases, to be a somewhat arbitrary part of the time and outside the other, though a posteriori assessment. being at CERN is the opposite because the field There is a sharp distinction in the style is in the tunnels!” After qualifying as a sur- of the second part of the book, which v e y or a n d s p e n d i n g t i m e d oi n g m e t r ol o g y for a requires training in physics or maths at c e m e nt pl a nt i n B u r m a a n d for t h e S or b o n n e i n advanced undergraduate level. These Paris, Missiaen arrived at CERN as a stagier in chapters begin with a discussion of the 1986. He never left, starting in a staff position Lorentz group. The interest then quickly working on the alignment of the pre-injector shifts to Wigner’s “little groups”, which for L E P, t h e n o f L E P it s e l f, a n d t h e n l e a d i n g t h e are subgroups of the Lorentz group with i nt e r n a l m e t r ol o g y o f t h e m a g n e t s for t h e L HC. the property of leaving the momentum From 2009–2018 he w as i n c ha rge of t he whole of a system invariant. Armed with this s u r v e y s e c t i o n, a n d s i n c e l a s t y e a r h a s a n e w r ol e mathematical machinery, the authors a s a c o or d i n a t or for s p e c i a l pr oj e c t s, s u c h a s t h e proceed to Dirac spinors and give a development of a train to remotely survey the Fieldwork Alban Vieille of the accelerators, survey and geodesy section aligning a LHC collimator. Lorentz-invariant formulation of the mag nets in t he arcs of t he LHC. harmonic oscillator that is eventually “B e i n g a s u r v e y or a t C E R N i s c o m pl e t e l y d i f- We see the physics meet ing an obstacle. applied to the parton model. The last fe r e nt t o o t h e r s u r v e y i n g j o b s,” e x pl a i n s M i s s i- The specialised nature of surveying at CERN chapter is devoted to a short discussion a e n. “We a r e a s k e d t o a l i g n c o m p o n e nt s w it h i n results as a success m e a n s t h e t e a m h a s t o s p e n d a l o t o f t i m e fi n d i n g on optical applications of the concepts a couple of tenths of a millimetre, whereas in the right people and training newcomers. “It’s advanced previously. Unfortunately, the normal world they tend to work with an that we share in too hard to measure at this level and to maintain the book finishes abruptly at this point, accuracy of 1–2 cm, so we have to develop new the accuracy over long distances, so when we without a much-needed final chapter and special techniques.” r e c r u it w e l o o k for p e o pl e w h o h a v e a fe e l i n g for to summarise the material and discuss this level of precision,” says Missiaen, adding future work, which, the previous chapters A history of precision T h e AC l i n e i s r e a l i s e d b y a n y l o n w i r e, w h i l e t h e that a constant feed of students is important. imply, should be plentiful. When building the Proton Synchrotron in the distance is measured using a device invented at “Ev e r y y e a r I g o b a c k t o m y e n g i n e e r i n g s c h o ol Young Suh Kim and Marilyn Noz’s 1950 s, e n g i n e e r s n e e d e d a n i n s t r u m e nt t o a l i g n CERN called t he “ecar tometer”. and give a talk about metrology, geodesy and book may struggle to find its audience. components to 50 microns in the horizontal Invention and innovation haven’t stopped. t o p o m e t r y a t C E R N s o t h a t t h e s t u d e nt s u n d e r- The contrast between the lay and expert plane. A device to measure such distances did The SMM group recently adapted a metrology stand there is something special they can do parts of this short book, and the very n o t e x i s t o n t h e m a r k e t, s o t h e e a rl y C E R N t e a m technique called frequency sweeping interfer- in their career. Some are not interested at all, specialised topics it explores, do not invented the “distinvar” – an instrument to ometr y for use in a cr yogenic environment to while others are very interested – I never find make it suitable for a university course, ensure the nominal tension of an invar wire align components inside the sealed cr yostats students in between!” though sections could be incorporated while measuring the small length to be added o f t h e f ut u r e H i g h-L u m i n o s it y L HC (H L-L HC), CERN’s SMM group has more than 120 peo- as additional material. It may well serve, to obtain the distance between two points. It which contract by up to 12 mm when cooled pl e, w it h a r o u n d 35 s t a ff m e m b e r s. C o nt r a c t or s however, as an interesting pastime was still used as recently as 10 years ago, says to operational temperatures. Another recent push the numbers up further during peri- for mathematically inclined audiences Missiaen. Another “stretched wire” technique i n n o v a t i o n, i n c ol l a b or a t i o n w it h t h e I n s t it ut e ods such as the current long-shutdown two who will certainly appreciate the for- developed for the ISR in the 1960s and still in of Plasma Physics in Prague that came about (LS2), during which the group is tasked with malism and clarity of the presentation u s e t o d a y r e pl a c e s s m a l l-a n g l e m e a s u r e m e nt s while developing the challenging alignment measuring all the components of the LHC in of the mathematics. by a short-distance measurement: instead of system for HIE-ISOLDE, is a non-diffractive the radial and vertical direction. “It takes measuring the angle between two directions, l a s e r b e a m w it h a c e nt r a l a x i s t h a t d i v e r g e s b y two years,” says Jean-Frederic Fuchs, who Nikolaos Rompotis University AB and AC, using a theodolite, it measures the just a few mm over distances of several hundred is section leader for accelerators, survey and of Liverpool. distance between the point B and the line AC. m e t r e s a n d w h ic h c a n “r e c o n s t r u c t” it s e l f a f t e r geodesy. “During a technical stop, we are in

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CCJulAug20_Reviews_v3.indd 52 24/06/2020 14:29 CCJulAug20_Careers_v2.indd 53 24/06/2020 12:03 CERNCOURIER www. V o l u m e 6 0 N u m b e r 4 J u l y /A u g u s t 2 0 2 0 CERNCOURIER.COM CERNCOURIER.COM PEOPLE CAREERS RECRUITMENT charge of the 3D-position determination of a surveyor’s job – post-treatment of the data The new beam-dump tunnels in the LHC and the components in the tunnels and their align- and planning for measurement campaigns is the freshly excavated HL-LHC tunnels in points ment at the level of a few tenths of a millimetre. also a big part of what we do.” 1 and 5 are also moving slightly compared to There is a huge number of various accelera- With experience in both experiment and the main LHC tunnel. “Today we almost know For advertising enquiries, contact CERN Courier recruitment/classified, IOP Publishing, Temple Circus, Temple Way, Bristol BS1 6HG, UK. tor elements along the 63 km of beam lines accelerator alignment, Fuchs knows all too well all the places where it moves,” says Fuchs. “For 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. at CERN.” the importance of surveying at CERN. Some sure, if you want to run the LHC for another Please contact us for information about rates, colour options, publication dates and deadlines. Fuchs did his master’s thesis at CERN in the areas of the LHC tunnel are moving by about 18 years there will be a lot of measurement domain of photogrammetry and then left to 1 mm per year due to underground movement and realignment work to be done.” His team work in Portugal, where he was in charge of inside the rock. The tunnel is rising at point also works closely with machine physicists to guiding a tunnel-boring machine for a railway 5 (where CMS is located) and falling between compare its measurements to those performed project. He returned to CERN in the early 2000s P7 and P8, near ATLAS, while the huge mass with the beams themselves. as a fellow, followed by a position as a project of the LHC experiments largely keeps them at It is clear that CERN’s accelerator infra- associate working on the assembly and align- the same vertical position, therefore requiring structure could not function at the level it does ment of the CMS experiment. He then left to significant realignment of the LHC magnets. without the field and office work of surveyors. join EDF where he worked on metrology inside During LS2, the SMM group plans to lower the “We see the physics results as a success that we nu c l e a r p o w e r pl a nt s, fi n a l l y r e t u r n i n g t o C E RN LHC at point 5 by 3 mm to better match the CMS share in too,” says Missiaen. “When the LHC as a staff member in 2011 working on accelerator interaction point by adjusting jacks that allow turned on you couldn’t know if a mistake had alignment. “I too sought a career in which I the LHC to be raised or lowered by around 20 mm been made somewhere, so in seeing the beam didn’t have to spend too much time in the office. in each direction. For newer installations, the go from one point to another, we take pride that I also liked the balance between measurements movement can be much greater. For example, we have made that possible.” and calculations. Using theodolites and other LINAC4 has moved up by 5 mm in the source equipment to get the data is just one aspect of area, leading to a slope that must be corrected. Matthew Chalmers editor. Appointments and awards

New director at PSI University Oxford from the UK’s national First Olga Igonkina travel Christian Rüegg, a solid-state laboratories and CERN being grant awarded physicist with a research focus affiliated with its research and Viacheslav Matiunin, a PhD on quantum phenomena in teaching programmes. student in experimental physics magnetism, took up the position at ITEP Moscow, has received the of director of the Paul Scherrer Turok takes up Higgs chair first Olga Igonkina travel grant Institute (PSI) in Switzerland on Theorist Neil Turok, previously for Russian talent in physics. 1 April, succeeding Joël Mesot. In director of the Perimeter Institute The €2000 award was established addition to its advanced X-ray and in Canada, has taken up the in memory of the late Russian– spallation–neutron sources, PSI inaugural Higgs Chair at the Dutch particle physicist Olga is host to rare-decay experiments Higgs Centre for Theoretical “Olya” Igonkina, a member of the such as MEG II (CERN Courier May/ Physics (HCTP) at the University ATLAS experiment and Nikhef

Jun 2019 p45) and Mu3e, and has a Institute Perimeter staff who passed away last year strong programme of searches for at the age of 45. Announced in new physics using high-intensity, May, Nikhef has also established, low-momentum pion and muon in Igonkina’s memory, a new

beams and ultracold neutrons. Nikhef Earlier this year, a team used pion Burrows heads JAI beams at PSI to make the first Philip Burrows of the University

Scanderbeg SauerScanderbeg Photography of Oxford has been appointed director of the John Adams Institute for Accelerator Science (JAI), a three-institute centre of excellence for Can you imagine working in a place like nowhere else on earth? advanced accelerator science and technology based at: the of Edinburgh. Building on the University of Oxford; Royal scientific legacy of Peter Higgs, CERN seeks to recruit the next ISOLDE Physics Group Leader Holloway, University of the HCTP was established in 2012 London; and Imperial College. with a vision to create bridges The on-line isotope mass separator ISOLDE is a facility dedicated to the production of a large variety of radioactive ion JAI’s core R&D programme between disciplines and combine beams for many different experiments in the fields of nuclear and atomic physics, solid-state physics, materials science covers beam dynamics, beam graduate-school education with and life sciences. The facility is located at the Proton-Synchrotron Booster (PSB) at CERN, the European Organization for instrumentation, feedback and research. Turok plans to promote control, RF systems, metrology new research directions including Nuclear Research. It is operated by the ISOLDE collaboration. and alignment systems, lasers the application of real-time path and plasmas, and medical integrals in general relativity, and three-year fellowship for a Full details of the position can be found on: http://cern.ch/go/Sc7X beamlines. The institute to lead a considerable expansion female post-doc researcher spectroscopic measurements currently comprises 20 faculty, of the centre’s activities, intended to encourage talented Deadline for applications: 30.09.2020 of exotic pionic-helium atoms 29 staff and 39 PhD students, including new faculty positions female physicists to pursue a (see p15). with an additional 33 staff and fellowships. career in science. CERN. Take part!

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ELI Beamlines research centre in Dolní Břežany is part We o er: Deutsches Elektronen-Synchrotron DESY of pan-European Extreme Light Infrastructure supporting A Research Centre of the Helmholtz Association scienti c excellence in Europe by making available its • the opportunity to participate in this unique scienti c capacities to the best scienti c teams across the world. project The ELI Beamlines is part of the Institute of Physics of • competitive and motivating salary the Czech Academy of Sciences. The High Field Initiative • Ž exible working hours For our location in Hamburg we are seeking: Faculty Position in the Medical Physics group at project at the ELI-BL is established to be the leading • career growth the Institute of Physics, project in the high  eld science. • lunch vouchers, pension contribution and 5 sick days DESY-Fellowships - Pontificia Universidad Católica de Chile. • support of leisure time activities Experimental Particle Physics The Institute of Physics at Pontificia Universidad Católica de Interviews will begin immediately and the position will stay open until  lled. DESY. Chile invites applications for a tenure-track full time faculty The HiFI-ERT (Excellence Research Team) recruits DESY is one of the world’s leading research centres for photon science, position at the Assistant Professor level in Medical Physics particle and astroparticle physics as well as accelerator physics. More a scientist for developing theory and computer or a closely related field. We are looking for candidates with simulations on the following activities: Applications, containing CV, cover letter, contacts of than 2700 employees work at our two locations Hamburg and Zeuthen in a strong background and research expertise in any subfield references, and any other material the candidate considers science, technology and administration. of physics applied to medical diagnosis and treatment and • theory of charged particle acceleration and hard relevant, should be sent to Particle physics and the investigation of the fundamental building blocks open to collaborate in interdisciplinary teams. A Ph.D. degree electromagnetic radiation in relativistic laser plasma Mrs. Jana Ženíšková, HR specialist of nature and their interactions are at the core of the DESY mission. We ([email protected], +420 - 601560322). take significant responsibility in internationally leading projects, e.g. in Physics or a closely related field is required. Postdoctoral • development and use of various computer codes for simulation of nonlinear processes in laser plasmas at CERN and at KEK, and on our campus. We develop detectors and experience is desirable. Information regarding the personal data processing and technologies relevant for our experimental activities, and we engage in The successful candidate is expected to be able to teach in Further questions on scienti c project can be addressed to access to the personal data at the IoP CAS can be found scientific computing and in the development of future accelerators for Spanish after one year. Applications must include curriculum Sergei Bulanov ([email protected]) on: https://www.fzu.cz/en/processing-of-personal-data. particle physics. vitae, list of publications, statements of proposed research and The position teaching interests, and two recommendation letters. Requirements: You are invited to take an active role in one or more of the following areas The recommendation letters must be sent directly by the • PhD in Physics or Mathematics with the focus on at Hamburg: referees to the e-mail provided below. l theoretical and computation physics related to Our involvements at CERN (ATLAS, CMS) and at KEK (Belle II) l nonlinear waves, charged particle acceleration, Experimental activities on-site (ALPS II and future on-site experiments) The successful candidate is expected to establish independent l quantum electrodynamics, numerical modeling of Preparations for future particle physics experiments, in particular research. The complete application should be sent by relativistic plasmas detector and technology development e-mail by July 31st, 2020 to the Search Committee at l Scientific computing [email protected]. l Accelerator development Requirements OCTOBERMARCH 2020 AND l Ph.D. in physics completed within the last four years Department of Space and Climate Physics l Interest in particle physics l Expertise relevant for at least one of the areas listed above Now accepting applications for: Image: NASA astronauts DESY-Fellowships are awarded for a duration of 2 years with the Graduate Careers repair the Hubble Space possibility of prolongation by one additional year. MSc Space Science and Engineering Target the best candidates for your graduate vacancy Telescope Futher informations and a link to the submission system for your The space industry is a multi-billion pound industry in the UK application and the references can be found here: Contact Natasha Clarke today to find out and is growing world-wide. In a programme taught by the UK’s http://www.desy.de/FellowFH how to get your vacancy noticed. largest university space science department, learn how to design Please note that it is the applicants responsibility that all material, a space mission from payload selection to launch and operation. including letter of references, reach DESY before the deadline for the E-mail [email protected] Tel +44 (0)117 930 1864 Taking the Space Technology pathway, you will learn cutting application to be considered. edge space applications for science and technology including mechanical Salary and benefits are commensurate with those of public service Powered by and electrical design of satellites. organisations in Germany. Classification is based upon qualifications and The Space Science pathway prepares you for a career in the exciting fields assigned duties. Handicapped persons will be given preference to other of experimental solar-, planetary-, or astro- physics. Learn how to design and equally qualified applicants. DESY operates flexible work schemes. DESY operate scientific instrument in space from scientists and engineers that work is an equal opportunity, affirmative action employer and encourages on ESA and NASA missions. applications from women. Vacant positions at DESY are in general open to part-time work. During each application procedure DESY will assess Find more information and apply at: bit.ly/MSSL_MSc whether the post can be filled with part-time employees. MSc Space Risk and Disaster Reduction Deadline for applications: 2020/09/30 In an increasingly technological and globally connected world, We are looking forward to your application via our application system: risks to space-based communications systems and critical www.desy.de/onlineapplication infrastructure are emerging threats to national security and businesses. Deutsches Elektronen-Synchrotron DESY Human Resources Department | Code: FHFE003/2020 This unique programme unites emergency response, disaster risk reduction Notkestraße 85 | 22607 Hamburg Germany and space technology, you will learn about satellite technology, mission Phone: +49 40 8998-3392 http://www.desy.de/career design, hazards and vulnerabilities unique to outer space, and the monitoring of hazards on Earth from outer space. Taught jointly with the Institute of Risk and Disaster Reduction, this programme is a blend of disaster science and space technology. Find more information and apply at: bit.ly/MSSL_MSc

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a programme of high-mass dimuon production CERN c ol l a b or a t i o n, m a k i n g s u r e t h a t t h e y w e r e v i s i bl e OBITUARIES with π+, π-, K+, K–, p and –p beams, enabling the at collaboration meetings and conferences. He first observation of upsilon production by pions. also imbued them and the whole collaboration It also probed the structure of the incoming with a culture of never publishing even prelim- particles via the Drell–Yan process. The spec- inary results before being absolutely certain of t r o m e t e r c a r r i e d o ut a s t r i n g o f v a lu a bl e e x p e r i- them. As a result, OPAL’s scientists built a strong Pierre Lazeyr as 1931–2020 ments under Aldo’s guidance until 1981, when he reputation, with many conference conversations became spokesperson of the OPAL experiment including the words, “let’s wait and see what OPAL being planned for LEP. Aldo remained at the h a s t o s a y”. A l d o’s f a it h i n t h e y o u n g e r g e n e r a t io n Talent, tenacity and warmth h e l m o f OPA L r i g ht u p t o h i s r e t i r e m e nt i n 1995. was rewarded by some 300 successful PhD theses OPAL was built around tried and tested technol- from OPAL, while more than 100 CERN fellows Pierre Lazeyras, who played leading roles in the U Schlatter with the superconducting magnet cryostat. ogy, including a paradoxical novelty for Morpurgo: passed through the collaboration over its lifetime. ALEPH experiment, neutrino beams and silicon Under Pierre’s supervision, a vacuum leak was a w a r m m a g n e t. Hu g e for it s t i m e, w it h a c ol l a b o - Aldo was a great leader, commanding respect detectors during a 35-year-long career at CERN, located, close to the edge of the magnet, and r a t i o n o f s o m e 300 p e o pl e, OPA L w a s n e v e r t h e l e s s and affection in equal measure. That the collab- passed away on 4 April aged 88. the cryostat then underwent “surgery” using the smallest of the four LEP experiments. It was Aldo Michelini during the LEPfest in October 2000. oration was still able to gather more than 100 Pierre graduated from the École supérieure de a milling machine suspended from a crane. It a scale that lent itself well to Aldo’s unique style members in 2019 to celebrate the 30th anni- physique et chimie industrielle (ESPCI) in Paris was a wonderful exercise in imagination and, to of m a n a ge me nt – lea d i ng t h roug h e x a mple a nd making tough choices, and winning over those versary of that first Z decay is testimony to the in 1954 and, after working in Anatole Abragam’s the relief of all, a complete success. Pierre had consensus. Colleagues remember him smiling who might init ially have disag reed w it h him. kind of person Aldo was, and to the spirit that he group at CEA Saclay, he joined CERN as a staff always insisted that such a huge superconduct- a n d l o o k i n g v e r y w or r i e d, or m or e o f t e n t h a n n o t, When OPAL detected the first Z boson at LEP on engendered. Although he was unable to attend member in October 1961. He was one of the early ing magnet and cryostat inherently constituted t h e o t h e r w a y a ro u n d. T h i s w a s s t r a n g e l y m o t i- 13 August 1989, Aldo was heard to remark that the that gathering, he sent a message, and was loudly collaborators in the Track Chamber (TC) division, a fragile device, and had objected to the idea of vational, with team members striving to make y o u n g p e o pl e h a d t a k e n o v e r. T h e a v e r a g e a g e o f c heered. He w ill be sorely missed. which built the two-metre bubble chamber and warming up the magnet during annual shut- him smile more and worr y less. His personalit y t h o s e i n t h e c o nt r ol r o o m t h a t d a y w a s w e l l u n d e r the Big European Bubble Chamber (BEBC). In downs, citing the mechanical stress resulting s h ap e d t he u n ique OPA L tea m s pi r it. D e s pite h i s 30, and that youthfulness was no accident. Aldo Rolf Heuer, David Plane and Mette Stuwe parallel, he headed the team that developed one from this procedure. He was absolutely right. gentle nature, Aldo was more than capable of actively supported the young members of the CERN (retired) and James Gillies CERN. of the first superconducting bending magnets Pierre was also involved in the design of the for BEBC’s “beam s3”. large stabilised superconductors for the LHC- A dolf Minten 1931–2020 Pierre directed the TC SPS neutrino beam experiment magnets and served as a member of group from 1972, which included the construc- the magnet advisory group of the LHC into his tion of the horns, the 185 m-long iron muon retirement, his wisdom being highly appreci- A scientific and technica l aut horit y shielding and the beam monitoring, for which Pierre at his retirement party in 1996. ated. He was also an active member of the CERN silicon-diode particle detectors were employed. Staff Association. Following his retirement in Distinguished CERN physicist Adolf Minten CERN t i o n a s E F d i v i s io n l e a d e r a n d j oi n e d t h e A L E PH After some initial teething troubles, the SPS those of us coming from smaller experiments. 1996, he joined the Groupement des Anciens and passed aw ay on 21 Marc h at t he age of 88. e x p e r i m e nt a t L E P. T h e L E P e x p e r i m e nt s w e r e a neutrino beams operated for nearly 20 years Pierre made sure we were realistic in our ambi- was a representative on the CERN health insur- After graduating from the University of Bonn, q u a nt u m l e a p i n s i z e a n d c o m pl e x it y w h e n c o m- without major problems. The silicon monitors tions and our estimates of the difficulties and ance supervisory committee, where his advice where he worked in the team of Wolfgang Paul on p a r e d t o pr e v io u s e x p e r i m e nt s, a n d d e m a n d e d were found to be more precise than the early gas- planning constraints, and we owe it mainly and opinions were always wise and measured. t h e 500 M eV e l e c t r o n s y n c h r o t r o n, A d ol f j oi n e d new organisational structures. As head of the fi l l e d io n c h a m b e r s, a n d t h i s w a s t h e b e g ing to him that the various parts of ALEPH were Pierre was not only highly talented and used t h e C E R N T r a c k C h a m b e r d i v i s i o n i n 1962. Wor k- ALEPH steering committee, Adolf was instru- of the era of silicon micro-strip detectors. Pierre assembled without major problems. He was his experience most effectively, he was also ing under Charles Peyrou, he set up beamlines mental in setting up an organisation whose role encouraged the microelectronics developments always available for advice even if, in his care- a warm person, someone on whom one could for t h e t w o -m e t r e b u b bl e c h a m b e r a n d a c t i v e l y he compared to an “orchestra, where it is not for this new technology and its integrated read- ful and reserved style, he did not try to direct always rely. He would always tell you straight participated in its broad physics programme. sufficient that all the instruments be properly out circuits. These advances also came just in or micro-manage everything. how things were and then suggest how any Another important milestone of his career was tuned, they must also harmonise”. However, time for the UA2 experiment at the SPS and for In addition to being responsible for gen- problems could be tackled. A typical remark by h i s t i m e a s a v i s it i n g s c i e nt i s t a t SL AC f r o m 1966 his true role of an “elder statesman” went far wider applications in the LEP experiments. eral safety in the experiment (which had no Pierre would be: “Ask me to approve or reject to 1967, where he took par t in t he early ex peri- beyond organisational responsibilities; equally Pierre was instrumental in the formation major incidents during its 11 years of opera- your ideas, do not ask me what work I have for ments on hadron electro-production and electron important were his human qualities, which and success of ALEPH. From the conception tion), Pierre ensured that the construction of you.” We will remember him as a very dear friend scat tering at t he new t wo-mile accelerator. were remarkable indeed and for which he was of the experiment in 1982 right through to the ALEPH was completed within budget. He also and colleague. Adolf returned to CERN at a time of deci- Adolf Minten addressing the crowd at one of the respected by bot h young and old. LEP2 phase in 1996, he was ALEPH techni- played an essential role at a crucial moment for sive developments in accelerator and detector famous EF division parties. A d ol f m a i nt a i n e d a c o n s t a nt i nt e r e s t i n DE S Y, cal coordinator – a role that was quite new to the experiment in the early 1990s: the problem His friends and colleagues at CERN. technologies. In parallel to his continued par- where he was highly appreciated. In 1981 Bjorn ticipation in bubble-chamber experiments, he electronics channels. Major detector, electronics Wiik’s study group had finished the HERA design a Ldo MicheLini 1930–2020 b e c a m e i nt e r e s t e d i n t h e p h y s i c s pr o g r a m m e o f a n d s o f t w a r e d e v e l o p m e nt s w e r e n e e d e d t o br i n g report, and DESY set up an international evalua- the Intersecting Storage Rings, the world’s first t his project into operat ion in 1974. t io n c o m m it t e e t o a n a l y s e it i n d e t a i l. A d ol f w a s proton–proton collider, which started operation In 1975, to prepare for t he nex t generation of i n v it e d t o c h a i r t h i s c o m m it t e e. It s p o s it i v e r e c- A respected leader in 1971. To cope wit h t he high interaction rates experiments at the new SPS machine, the CERN ommendation was a significant step towards the expected at this new machine, the development management proposed the creation of a new a p pr o v a l o f t h e H E R A pr oj e c t. He c h a i r e d t h e DE S Y Aldo Michelini, who led OPAL and other impor- ber magnet with spark chambers, which he then superconducting magnet that could be arranged of track detectors focused on the multi-wire Experimental Facilities (EF) division. Adolf was scientific council from 1987 until 1990, during tant experiments at CERN, passed away at Easter used as part of a CERN/ETH/Imperial College/ and configured according to the physics to be proportional chamber (MWPC) developed by e l e c t e d t o l e a d t h e n e w E F d i v i s i o n, a p o s it i o n t h a t the main construction phase of the storage rings at the age of 89. He was known as much for his Saclay collaboration to measure properties of studied. Omega was initially equipped with G e or g e s C h a r p a k . O n e o f t h e d e s i g n s w a s a l a r g e re qu i re d a c om bi n at ion of s t ron g s c ie nt i fic a nd and the H1 and ZEUS multi-purpose detectors. 0 – - kindness and care for his colleagues, particu- the K2 meson and p p and K p charge-exchange spark chambers and installed on a PS beamline, multi-purpose spectrometer called the split-field t e c h n i c a l a ut h or it y, a n d i n w h i c h h e c o m m a n d e d A d ol f r e t i r e d f r o m C E R N i n 1996. We r e m e m b e r larly those embarking on their careers, as for interactions using a polarised target. receiving its first beam in 1972, and moved to m a g n e t (SF M). A t t h a t t i m e, a l a r g e-s c a l e a p pl i- t h e u n r e s e r v e d r e s p e c t o f h i s c ol l a b or a t or s. Fol- him as a supremely well-organised scientist of the physics at which he excelled. As the 1960s advanced, Aldo formed a partner- the SPS in 1976 where it became the backbone of cation of the revolutionary MWPC technology, l o w i n g s u p p or t pr o v i d e d t o t h e m aj or f a c i l it i e s for d e e p a n d i nc i s i v e i nt e l l i g e nc e, u n a f r a id t o c h a l- Aldo first came to CERN in 1960, bringing ship and life-long friendship with his compa- t h e fi x e d-t a r g e t pr o g r a m m e t h e r e for 20 y ears. hitherto available only in single-wire devices or t h e SP S fi x e d-t a r g e t pr o g r a m m e, s u c h a s BE B C, lenge and question preconceived ideas, and always experience from several tracking-chamber triot, Mario Morpurgo, who was an early pioneer In 1973, Aldo headed a similar project to build small-surface detectors, presented a formidable the Omega spectrometer and the neutrino, muon i n s pi r i n g o t h e r s t o d o t h e s a m e. A t t h e s a m e t i m e, experiments, including a stint with Jack Stein- of superconducting magnet technology. The a general-purpose spectrometer for the North c h a l l e n g e. I n 1969, A d ol f b e c a m e r e s p o n s i bl e for and other experiments, his new division soon he was a modest person who cared profoundly berger at Columbia University, and he lost no two were part of the small team spearheading Area. This became NA3, which was the first the construction of the SFM facility, which cov- became involved in the successful experiments for a l l t h e p e o pl e a r o u n d h i m, a n d t h e i r f a m i l i e s. time in making an impact. One of his earliest the development of the Omega spectrometer, experiment to receive beam in the new SPS had- ered the full solid angle with an unprecedented at t he SPS proton–ant iproton collider. s contributions was to equip CERN’s Wilson cham- a general-purpose device built around a large ron hall, EHN1, in May 1978. NA3 embarked on 300 m2 detector surface, and 70,000 wires and In 1984 Adolf stepped down from his posi- His friends and colleagues.

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PEOPLE OBITUARIES PEOPLE OBITUARIES

A ntonino PulliA 1935–2020 policy committees, including the European CERN Physical Society HEPP board (2006–2013) and the CERN scientific policy committee (2012– From neutral currents to dark matter 2017). Outside academia, she was a member of several Spanish ministerial scientific panels Antonino Pullia, who passed away in April aged Pullia family out that the predicted background was far and of the technical and research panel of the 84, was a student of Giuseppe Occhialini at the too small to explain the observed number of Princesa de Asturias awards. She also held an University of Milan and obtained his laurea in neutral-current candidates and thus, at the honorary doctorate from the Menéndez Pelayo 1959. For the next 60 years he devoted himself end of July 1973, the collaboration was able to International University, received the silver to teaching, administration and the rich physics announce the great discovery of neutral cur- medal of the University of Cantabria and the research programmes at the INFN and the uni- rents. The Italian Physical Society awarded the first Jul io Peláez aw ard for fema le pioneers in versities of Milan and Milano-Bicocca, playing 2011 Fermi prize to Pullia in recognition of his science, among other recognitions. a major role in establishing the new physics important contribution. Teresa’s influence on the Santander HEP department at the latter. He had a great passion At the beginning of the 1980s Tonino, as he group and the IFCA institute that she directed for teaching undergraduates, continuing well was known, joined the DELPHI collaboration until a few months before her death remains into retirement. at LEP where he worked with his group on the very visible. During her tenure, the group grew Pullia’s research ranged over many topics construction of the electromagnetic calorime- considerably and greatly expanded its activ- including neutrino physics, proton decay, ter, along with the reconstruction and analysis ities. The institute was awarded the greatest double-beta decay, DELPHI at LEP, CMS at LHC software. The Milan group, under his constant distinction of excellence of the Spanish science and dark-matter searches. He also played a support, was extremely active in DELPHI, pro- system, the Maria de Maeztu grant, and the Teresa Anoro in the CMS control room. prominent role in the discovery of neu- posing many original analyses, as well as many gender-equality prize awarded by the Spanish tral currents at CERN using the Gargamelle PhD and master theses, contributing to the National Research Council. approachable, righteous and sympathetic vision and her ability to mentor rising col- bubble chamber. exceptionally rich LEP physics results. Those of us who were fortunate enough she was, though with a strong character that leagues. She will be sorely missed. In March 1972 he presented the vertex In 2012 Tonino became interested in the to know Teresa and to share some of her came from her deep honesty. Teresa’s legacy distribution of possible neutral-current events detection of dark matter, deciding to resurrect scientific passions, are aware of how kind, stands as a testament to her leadership, her Her colleagues and friends. that had no lepton candidate but one or more a special type of bubble chamber developed pions. The distribution was seen to be uni- Tonino Pullia played a prominent role in the 50 years ago – called “the Geyser” – which is Danila Tlisov 1983–2020 form, just like the events with muon candidates, discovery of neutral currents at CERN. remarkable in its simplicity. With no moving leading immediately to the formation of work- parts, and the ability to reset itself a few seconds ing groups concentrating on neutral-current after a bubble is formed, the device was ideal A unique mix of strengths searches in both hadronic and purely leptonic He was always for underground experiments. He also formed modes. After a remarkable scanning and meas- the MOSCAB collaboration, which successfully Danila Tlisov, a member of the CMS collabora- Smith/CMS C urement effort many candidates for neutral extremely kind produced a small detector with the required tion at CERN, passed away on 14 April in Russia currents had been found, but the burning issue superheat needed for dark-matter searches. due to complications associated with COVID-19. was the size of the background due to neutron and open to Each of us who had the privilege to work with, He was just 36 years old. interactions. Pullia recognised the importance alternative views or simply to talk to, Tonino has been enlight- Danila joined the INR Moscow group in 2010 as of a special class of events, namely genuine e n e d i n s o m e w a y i n o u r e ffor t s t o h a v e a d e epr a young researcher after graduating with honours neutrino events with a detected final-state understanding of fundamental physics. He was from Moscow State University and defending his muon and a neutron emitted at the interac- always extremely kind and open to alternative dissertation. Following his contributions to early tion vertex and detected downstream in the a neutron. It was clear that the major source views. We will sadly miss him for his human heavy-neutrino searches, he started to work on visible part of the bubble chamber. Such events of background neutrons was coming from qualities, and as a physicist. the CMS hadron calorimeter (HCAL) subsystem were rare, but very valuable, since in this case neutrino events in the material surrounding in 2012. Danila served as the hub of the multi- the downstream event was surely induced by Gargamelle. With this knowledge, it turned His friends and colleagues. national CMS HCAL upgrade effort, leading the CERN-based team that received individual teresA rodrigo A noro 1956–2020 components from India, Russia, Turkey and the US, and assembling them into a working detec- tor. Danila recently brought his unique mix of Shaping Spanish particle physics strengths to the CMS HCAL management team as deputy project manager and a member of the Teresa Rodrigo Anoro, professor of atomic and the Uranium–TMP calorimeter for the upgrade More recently, moving away from hadron CMS management. nuclear physics at the University of Cantabria, of the UA1 experiment, where she started b e a m s for t h e fi r s t t i m e, Te r e s a pr o m o t e d n ew In the physics analysis realm, Danila worked passed away at her home on 20 April after a her personal journey towards finding the approaches to the search for light dark-matter with the University of Rochester group on a long illness. She was a leading figure within top quark. This eventually brought her to the at the DAMIC experiment. She was well aware measurement of the electroweak mixing the particle-physics community and played a CDF experiment at Fermilab, where she car- of the importance of technology development angle using the forward–backward asym - key role in shaping Spanish particle-physics ried out the detailed modelling of the W+jet and detector building in high-energy physics metry in Drell–Yan events, where he focused policy, with an emphasis on promoting the background, a crucial input to the top’s dis- and orchestrated her group’s contribution to the on critical improvements to the calibration participation of women in science. covery. In 1994 she took up a faculty position construction of the CMS muon spectrometer, in of the electron-energy measurements in Danila Tlisov was instrumental in the CMS HCAL upgrade. After her bachelor’s degree in physics from at the Instituto de Física de Cantabria (IFCA) particular its muon alignment system, and to challenging regions of Drell–Yan kinematic the University of Zaragoza, Teresa joined in Santander, incorporating the IFCA group t he bu i ld i ng of CDF’s t i me-of-fl ig ht de te c tor. phase space. Danila was an accomplished backcountry tion, even during times of intense pressure. He the high-energy physics group of La Junta into both the CDF experiment and the newly Teresa’s scientific insight and strong com- CMS friends and colleagues remember touring skier. Because of his great physical challenged us with his brilliant ideas, guided de Energía Nuclear in Madrid (currently formed CMS collaboration at CERN. Under her mitment to whatever endeavour she was fo n d l y t h e w a r m s m i l e a n d i n c r e d i bl y e ffe c t i v e strength and focus on climbing, it was often students with patience and grace, and inspired CIEMAT), earning a PhD in 1985 with a thesis direction, the group continued her study of engaged in were recognised by the interna- leadership of Danila. His practical know-how said that he may have been faster going uphill us all. He will be sorely missed. on the production of strange particles at the the properties of the top quark and opened up tional community: she was elected chair of and excellent judgement were critical as we than downhill, and that is saying a lot. NA23 experiment at CERN. She then moved a new line of research towards the discovery the CMS collaboration board (2011–2012) and worked together through the tough challenges Among his many colleagues, Danila will be His colleagues and friends from the s to CERN to participate in the development of of the Higgs boson. served as a member of several scientific of a major detector upgrade. remembered for his pleasant, cheerful disposi- CMS collaboration.

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Notes and observations from the high-energy physics community Particle of doubt From the archive: July/August 1980 CERN unlocked Contemporary classical music CERN 81-6-80 CERN 68-6-80CERN 99-6-80 CERN is the latest addition to Fermilab’s rich cultural life in physics. Inaugural guest- composer David Ibbett’s latest oeuvre, Particle of Doubt, is a sonification of the evolving flavour f r ac t ion s i n t he neut r i no Left: Research DG Léon Van Hove fires the starting pistol; middle: the runners beam of the lab’s flagship In DUNE David Ibbett (left), alongside get under way; right: Executive DG John Adams presents the Challenge Trophy. long-baseline neutrino facility, fellow artists in residence Patrick First collisions in the Berkeley/Stanford PEP electron–positron which is preparing to send a Gallagher and Chris Klapper, in front of storage ring on 4 May were celebrated on the cover of CERN Courier beam 810 km from Chicago to part of DUNE’s short-baseline detector. July/August 1980. Also reported was a world record in the DUNE detector in South centre-of-mass energies on 21 May, when CERN’s Intersecting Dakota (see p32). Violin, viola and cello parts map the fractions of the electron, muon and tau eigenstates to the pitch of the melody, while Storage Rings collided two beams of 62 GeV alpha particles. flutes play rhythms taken from an estimate of the three neutrino Then, June saw an event we can only dream of during these masses – assuming normal ordering. “You should be massless like locked-down days. Not a first but a 10th – CERN’s annual relay race. rays of light,” sings soprano Beth Sterling, as the wavefunction Were you there? Did you run? Did you drop the baton? To paraphrase evolves. “You should be changeless, but the change gives us hope Baron Pierre de Coubertin: “The most important thing in the CERN that we’ll know where we came from,” she continues, referring to the race is not winning but taking part …” potential of the DUNE experiment to quantify leptonic CP violation. Pictured above are some reminders of that sunny “I don’t often write lyrics,” explains Ibbett, “but was so moved by day when the Laboratory, with double Directors- what I’ve learned about neutrinos, the infinitesimally small particles General and staff physically distanced across two that raise such huge questions, that the song found its way into sites, indulged in some social gathering. The race existence.” The piece will premiere in full in a live concert 2021. would have had its Golden Jubilee in 2020 but … here’s to taking part in the renormalised 50th in 2021. The predicted muon  Based on CERN Courier July/August 1980, pp187–188, p194 and p206. anomalous magnetic moment based on a 116 591 810 new consensus from Media corner have been caused by reflections the theory community of Askaryan-effect radio waves at –11 density interfaces between layers (arXiv:2006.04822), which “Maiman’s letter consists of two (43) × 10 of compressed snow, or firn. is lower than the current simple figures and fewer than experimental value by 300 words, and – unlike many “I think we’re seeing a real change 3.7 standard deviations modern submissions – there is no here in what particle physics is concluding paragraph announcing about. It’s not about adding more the many scientific and technological particles to a long list of particles; Les Horribles advances the finding may lead to.” it’s about how does the universe Cernettes From an editorial in Nature Reviews really operate in a fundamental Physics (vol 2, p221) celebrating way to produce what we see today?” reunite online 60 years of the laser, proposed Fermilab’s Joe Lykken quoted in an by Theodore Maiman in a paper article about neutrino physics in Dedicated in solidarity titled “Stimulated optical Gizmodo (20 May). to everyone in lockdown radiation in ruby”. around the world due “It wasn’t a hard decision for arXiv to COVID-19, CERN’s “We think sub-surface firn is to join the strike.” infamous musical spinout the culprit.” Astroparticle physicist Eleonora Les Horribles Cernettes Ian Shoemaker of Virginia Tech, Presani, executive director of – famous for such earworms as “Collider”, “Strong Interactions” quoted in New Atlas (11 June), the arXiv e-print repository, and “Microwave Love” – have released “The Lockdown Song” on proposing that two bizarre, but quoted in Nature (9 June) on the YouTube. “I’m running out of protons now the synchrotron’s shut,” apparently neutrino-like, high- decision by many academics and sing the self-styled world’s only high-energy rock band energy events recorded at the organisations to cease research (clockwise from top left: Colette Marx-Neilsen, Angela Higney, South Pole by the ANITA balloon activities on 10 June to reflect on Michele de Gennaro and Lynn Veronneau). experiment in 2016 and 2018, may systemic inequalities in science.

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