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WELCOME V OLUME 5 7 N UMBER 3 A PRIL 2 0 1 7 CERN Courier – digital edition Welcome to the digital edition of the April 2017 issue of CERN Courier. Theory in motion Few scientific disciplines enjoy such a close connection with mathematics as particle physics, and at the heart of this relationship lies quantum field theory. Quantum electrodynamics famously predicts quantities, such as the anomalous magnetic moment of the electron, which agree with observations at the level of 10 decimal places, while the Higgs boson existed on paper half a century before the Large Hadron Collider (LHC) flushed it out for real. Driven by the strong performance of the LHC experiments, there has been a burst of activity in recent months concerning next-to-next-to-leading order (NNLO) calculations in quantum chromodynamics to ensure that theory keeps up with the precision of LHC measurements. As the cover feature in this issue explains, cracking the complex NNLO problem demands novel algorithms, mathematical ingenuity and computational muscle. Theorists are also trying to make sense of a number of “exotic” hadrons that have turned up in recent years in experiments such as LHCb and which do not naturally fit the simple quark model. Sticking with the strong-force theme, we also report on 30 years of heavy-ion physics and how recent measurements at the LHC and RHIC are closing in on the evolution of the quark–gluon plasma. Finally, we describe new forward detectors that from this year will allow the LHC to analyse photon–photon collisions in the ongoing search for new physics.

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To subscribe to the magazine, the e-mail new-issue alert, please visit: http://cerncourier.com/cws/how-to-subscribe. HEAVY IONS EQUALITY TWO-PHOTON Thirty years of Refl ections on ultrarelativistic gender at CERN PHYSICS EDITOR: MATTHEW CHALMERS, CERN collisions over the decades Turning the LHC into a DIGITAL EDITION CREATED BY DESIGN STUDIO/IOP PUBLISHING, UK p26 p5 photon collider p23

CCApr17_Cover.indd 2 08/03/2017 15:23 CERNCOURIER www. V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 CERN Courier April 2017 Contents Power Supply Beamline Electronic Systems Instrumentation • Digital Current Regulation Loop: easiness to adapt • TURN-KEY Solution for Photon Beam Position Covering current developments in high-energy to any load condition Monitors and for Power Supply System for Optics physics and related fi elds worldwide • High Modularity and Extreme Configurability • BEST - Beamline Enhanced Stabilization System CERN Courier is distributed to member-state governments, institutes and laboratories affi liated with CERN, and to their personnel. It is published monthly, except for CERNCOURIER January and August. The views expressed are not necessarily those of the CERN • Ethernet Connectivity • Low Noise and High Resolution management. • Firmware Remote Update • Ethernet Connectivity Editor Matthew Chalmers V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 Books editor Virginia Greco CERN, 1211 Geneva 23, Switzerland E-mail cern[email protected] Fax +41 (0) 22 76 69070 5 V i E W p O i n t Web cerncourier.com Advisory board Peter Jenni, Christine Sutton, Claude Amsler, 7 n E W s Philippe Bloch, Roger Forty Sri Lanka signs International Co-operation Agreement with Laboratory correspondents: • Argonne National Laboratory (US) Tom LeCompte CERN European computing cloud takes off Milestone for US Brookhaven National Laboratory (US) Achim Franz • • Cornell University (US) D G Cassel dark-matter detector • European organisations uphold scientifi c DESY Laboratory (Germany) Till Mundzeck values Chamonix event prepares for LHC’s future CMS EMFCSC (Italy) Anna Cavallini • • Enrico Fermi Centre (Italy) Guido Piragino undergoes tracker transplant ATLAS reveals more strangeness Fermi National Accelerator Laboratory (US) Katie Yurkewicz • Forschungszentrum Jülich (Germany) Markus Buescher in the proton ALICE measures shape of the QGP fi reball at GSI Darmstadt (Germany) I Peter • IHEP, Beijing (China) Tongzhou Xu freee-out Rare decay puts Standard Model on the spot BaBar IHEP, Serpukhov (Russia) Yu Ryabov • • INFN (Italy) Antonella Varaschin casts further doubt on dark photons Jefferson Laboratory (US) Kandice Carter JINR Dubna (Russia) B Starchenko KEK National Laboratory (Japan) Saeko Okada 15 s CiEnCEWatCh Lawrence Berkeley Laboratory (US) Spencer Klein Los Alamos National Laboratory (US) Rajan Gupta NCSL (US) Ken Kingery 16 a s t r O W a t C h Nikhef (Netherlands) Robert Fleischer Novosibirsk Institute (Russia) S Eidelman Orsay Laboratory (France) Anne-Marie Lutz F E a t u r E s PSI Laboratory (Switzerland) P-R Kettle Saclay Laboratory (France) Elisabeth Locci 18 The two-loop explosion Science and Technology Facilities Council (UK) Jane Binks SLAC National Accelerator Laboratory (US) Farnaz Khadem NNLO calculations keep pace with precision of LHC experiments. TRIUMF Laboratory (Canada) Marcello Pavan

Produced for CERN by IOP Publishing Ltd 23 Looking forward to photon–photon physics IOP Publishing Ltd, Temple Circus, Temple Way, Bristol BS1 6HG, UK Detectors will probe the quartic couplings of electroweak bosons. Tel +44 (0)117 929 7481

Publisher Susan Curtis 26 A 30-year adventure with heavy ions Production editor Lisa Gibson Technical illustrator Alison Tovey Heavy-ion physics could be about to enter a new paradigm. Group advertising manager Chris Thomas Advertisement production Katie Graham Exotic hadrons bend the rules Marketing & Circulation Angela Gage 31 Half a century after the quark model Head of B2B & Marketing Jo Allen Art director Andrew Giaquinto was devised, a number of hadrons

Advertising appear to challenge its axioms. Tel +44 (0)117 930 1026 (for UK/Europe display advertising) But are they truly exotic? or +44 (0)117 930 1164 (for recruitment advertising); E-mail: [email protected]; fax +44 (0)117 930 1178

General distribution Courrier Adressage, CERN, 1211 Geneva 23, Switzerland E-mail: [email protected] 37 F a C E s & p L a C E s In certain countries, to request copies or to make address changes, contact: China Ya'ou Jiang, Institute of High Energy Physics, PO Box 918, Beijing 100049, People’s Republic of China 44 r E C r u i t M E n t E-mail: [email protected] Germany Antje Brandes, DESY, Notkestr. 85, 22607 Hamburg, Germany E-mail: [email protected] 47 B O O k s h E L F UK Mark Wells, Science and Technology Facilities Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1SZ E-mail: [email protected] 49 i n s i d E s t O r y MTCA.4 Precision Current US/Canada Published by Cern Courier, 6N246 Willow Drive, St Charles, IL 60175, US. Periodical postage paid in St Charles, IL, US MicroTCA for Physics Measurements Fax 630 377 1569. E-mail: [email protected] POSTMASTER: send address changes to: Creative Mailing Services, PO Box 1147, 50 a r C h i V E St Charles, IL 60174, US • New standard for industry and science • Precision current measuring transducers with closed-loop current transformer technology (Zero Published by European Organization for Nuclear Research, CERN, I NTERNATIONAL J OURNAL OF H IGH -E NERGY P HYSICS • Infrastructure for management of Rear Transition 1211 Geneva 23, Switzerland CERNCOURIER

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HEAVY IONS EQUALITY TWO-PHOTON Graphic treatment of NNLO diagrams relevant to LHC physics. Thirty years of Refl ections on On the cover: ultrarelativistic gender at CERN PHYSICS collisions over the decades Turning the LHC into a p26 p5 photon collider p23 (Image credit: Daniel Dominguez.)

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ESFR_Ottobre_2016.indd 1 06/03/17 16:56 CCApr17_Contents.indd 3 08/03/2017 15:25 CERNCOURIER www. V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 CERN Courier April 2017 Viewpoint Accelerating gender equality The growing numbers of female colleagues at CERN marks significant changes in attitude.

behaviour varied greatly. We were often accused of exaggerating the need for gender-neutral language or reproached for no longer having a sense of humour. Although some women colleagues found themselves in the uncomfortable situation of wishing to support EO initiatives while not wishing to risk the perception of tokenism or positive discrimination, many became vital allies in moving the EO agenda forward. Whether it was a question of work–life balance or simply accepting women in all job categories, a great deal of effort was invested to overcome resistance born of years of habit. It has only been over time that the proportion of female scientists at CERN has risen We all need to join forces to By Sudeshna Datta-Cockerill to match the numbers in society, as reflected by our assure CERN’s ongoing world-wide user community. commitment to diversity. When I started working at CERN in 1976, women were CERN’s EO programme itself has also evolved into a relatively rare sight. The few women who did work today’s diversity programme, which was launched in here generally held administrative roles, many having 2010 together with a newly created ombudsperson started with the incongruous job title of “scanning function and a formal harassment investigation panel. girls”, regardless of the age at which they had been The CERN code of conduct was also produced at this recruited. Back then it was quite normal to walk into time. The growing numbers of female colleagues in a workshop and find pictures of naked females on the all fields at CERN is living proof that we have come a walls, and everyday sexism was common. I recall once long way in the last two decades. But gender equality being told that women couldn’t possibly do night shifts means more than just gender parity. While continuing in the control room. The reason, a male colleague our efforts to encourage female students to pursue explained, was to avoid mysterious calls in the middle science and to employ our colleagues through of the night: “What if there was a problem and she has equitable recruitment practices, we should ask if we to call a physicist? What would his wife think?” are doing everything possible to promote a mindset Such attitudes were not just true of CERN, of that enables all our colleagues to contribute as equals. course, and things have changed significantly since The last six years have seen approximately then. Even as recently as 1995, less than three per equal numbers of male and female visitors to the cent of CERN research and applied physicists ombud office. However, when mapped against the were female, whereas today that number is around corresponding staff-member populations, there are 18 per cent. Similar increases have been seen across proportionally three-to-four times more women engineering and technician roles, and CERN now than men consulting the ombudsperson. A similar has its first female Director-General. pattern is seen in other international organisations It was in 1996 that CERN launched its equal where women are a minority, and is mirrored opportunities (EO) programme. I was appointed as the by the proportionally higher number of females first EO officer, and the following year an EO advisory who participate in CERN’s “diversity in action” panel was created. Many a meeting was taken up by workshops. Although the issues raised by women educating male colleagues about the lasting effects are essentially the same as those faced by their male Sudeshna of sexist behaviour through the personal experiences colleagues, a closer examination reveals examples of Datta-Cockerill of their female counterparts. The EO programme stereotyping and unconscious bias that suggests ours is the CERN adopted a four-pronged strategy focusing on is not yet a completely level playing field. ombudsperson. recruitment, career development, work environment Not only is it difficult for the majority to recognise She has worked at and harassment. On recruitment we took a firm stand the insidious barriers of organisational culture faced CERN for 41 years as HR adviser, against quotas, recommending instead thorough by minority groups, it is sometimes equally difficult head of learning and development, monitoring that would ensure reasonable proportions for those within the minority to bring these aspects to diversity programme leader, and of qualified women were shortlisted for interview. light. If we are to ensure that our work environment member of the HR management Equitable recruitment practices that we take is equally supportive to all, the experience of women board. She was CERN’s first for granted today were then the subject of much needs to be shared with a wider audience including equal opportunities officer debate. The multicultural nature of CERN brought their male colleagues. We all need to join forces to (1996–2003). added complexity, as people’s notions of acceptable assure CERN’s ongoing commitment to diversity.

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CERN Courier April 2017 News

I nternatIonal Sri Lanka signs International Co-operation Agreement with CERN M Brice/CERN On 8 February, Sri Lanka and CERN entered into an International Co-operation Agreement (ICA) concerning scientific and technical co-operation in high-energy physics. The agreement was signed by Susil Premajayantha, Sri Lankaʼs hon. minister of science, technology and research, and Charlotte Warakaulle, CERNʼs director for international relations. The new agreement follows an Expression of Interest signed in June 2015 by Sri Lanka ambassador Ravinatha Aryasinha and the then Director-General Rolf-Dieter Heuer, which already incorporated Sri Lanka into CERN’s high-school teacher and summer-student programmes. Previously, scientists from Sri Lankan universities have participated in LHC experiments within the frameworks of sabbatical leave or similar programmes, whereas others have participated as visiting Susil Premajayantha and Charlotte scientists employed by universities in a Warakaulle with the signed documents. Sommaire en français third country. With the partnership now formalised via says Warakaulle. “It is significant to see Le Sri Lanka signe un accord de coopération 7 the new ICA, students, scientists, engineers that a smaller, developing country is international avec le CERN and research institutes in Sri Lanka will emphasising fundamental research and Le nuage informatique européen prend 7 be able to benefit from broader and more making the connection with CERN a son envol sustained participation in CERN, and thus priority. It testifies to an understanding of be exposed to cutting-edge technology and the value of fundamental research, which Une étape importante pour un détecteur de 8 research in high-energy physics. is commendable in a country that is facing matière noire aux États-Unis “ICAs help to strengthen the global other challenges. It also further enhances Les organisations européennes défendent 9 network for particle physics, which is the CERN connection with South Asia, les valeurs scientifiques essential for the future of the discipline and following the associate memberships of Early registration deadline 15th May for fundamental research more generally,” Pakistan and India.” L’avenir du LHC se prépare à Chamonix 9 CMS se fait greffer un nouveau 10 o m p u t I n g C trajectographe European computing cloud takes off ATLAS dévoile davantage d’étrangeté dans 11 le proton A European scheme to make publicly the aim of the EOSC is to establish a ALICE mesure la forme de l’état final des 11 funded scientific data openly available Europe-wide data environment to allow « boules de feu » de plasma quarks-gluons has entered its first phase of development, scientists across the continent to exchange with CERN one of several organisations and analyse data. As well as providing Des désintégrations rares mettent à 12 poised to test the new technology. Launched the basis for better scientific research and l’épreuve le Modèle standard in January and led by the UK’s Science making more efficient use of data resources, BaBar sème davantage le doute sur les 12 and Technology Facilities Council, a the open-data ethos promises to address photons noirs €10 million two-year pilot project funded societal challenges such as public-health by the European Commission marks the or environmental emergencies, where Observation d’hydrogène métallique 15 first step towards the ambitious European easy access to reliable research data may Des lentilles gravitationnelles remettent en 16

Open Science Cloud (EOSC) project. improve response times. s question le rythme de l’expansion cosmique http://www.eps-hep2017.eu/ With more than 30 organisations involved, The pilot phase of the EOSC aims to Exhibition space still available 7

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CERN Courier April 2017 CERN Courier April 2017 News News

establish a governance framework and build P o l i c y the trust and skills required. Specifically, the pilot will encourage selected communities to develop demonstrators to European organisations uphold scientific values showcase EOSC’s potential across various research areas including life sciences, More than 50 science organisations in Europe Any measure that restricts the freedom of energy, climate science, material science have written an open letter expressing concern movement and communication of our US and the humanities. Given the intense about the impact of recent US policies colleagues will have a profound impact on computing requirements of high-energy on science, research and innovation. The science and innovation in Europe and other physics, CERN is playing an important role 10 February letter, which was organised by continents.” in the pilot project. EuroScience (founder of the EuroScience Three chief concerns are outlined in The CERN demonstrator aims to show that Open Forum, ESOF), asks that the principles the letter: the recent Executive Order the basic requirements for the capture and and values that underpin scientific progress discriminating against persons on the basis long-term preservation of particle-physics are upheld. It is addressed to the presidents of their nationality; indications that US data, documentation, software and the of the European Council and European government scientists might be affected by environment in which it runs can be satisfied Commission, and prime ministers and science new policies that limit their communication by the EOSC pilot. “The purpose of CERN’s ministers in individual European countries. In response to recent US policies, European with the press; and the unwarranted involvement in the pilot is not to demonstrate The European Physical Society (EPS) is science organisations seek to maintain a credibility given to views that are not based that the EOSC can handle the complex among the many signatories of the letter, as global science system based on core on facts and sound evidence in areas such as and demanding requirements of LHC are the Marie Curie Alumni Association, principles. climate science. It states that all of these are at data-taking, reconstruction, distribution, Scope of the pilot phase for the European Open Science Cloud. the Royal Society and the Royal Swedish odds with the principles of transparency, open re-processing and analysis,” explains Jamie Academy of Sciences. Explaining the and political barriers. In our globalised communication and the mobility of scholars Shiers of CERN’s IT department. “The rapid expanse in the quantities of open data and service quality, complements the work decision to sign, outgoing EPS president world, where international scientific and scientists, “which are vital to scientific motivation for long-term data preservation is being produced by science is stretching the of the Research Data Alliance and builds on Christophe Rossel says: “Science was and collaboration has become the rule, there is progress and to the benefit of our societies, for reuse and sharing.” underlying IT services,” says Jones. “The the European Strategy Forum on Research will never be restrained by physical, cultural no place for discrimination and censorship. economies and cultures deriving from it”. Propelled by the growing IT needs of the Helix Nebula Science Cloud, led by CERN, Infrastructure (ESFRI) road map. “Our LHC and experience gained by deploying is already working with leading commercial goal is to make science more efficient and l H c n e w s scientific workloads on commercial cloud cloud service providers to support this productive and let millions of researchers to prepare the LHC to run at 14 TeV during services, explains Bob Jones of CERN’s growing need for a wide range of scientific share and analyse research data in a Chamonix event CERN Run 3 with the experiments expressing IT department, CERN proposed a model use cases.” trusted environment across technologies, a clear preference to make the change in for a European science cloud some years The challenging EOSC project, which disciplines and borders,” says Carlos prepares for energy in a single step. ago. In 2015 this model was expanded and raises issues such as service integration, Moedas, EC commissioner for research, Regarding the longer-term future of endorsed by members of EIROforum. “The intellectual property, legal responsibility science and innovation. LHC’s future the LHC, the High-Luminosity LHC (HL-LHC) demands challenging proton F a c i l i t i e s and ion beam parameters from the injector 2016 was a remarkably successful year for complex. The LHC injector upgrade Milestone for US dark-matter detector CERN’s Large Hadron Collider (LHC), (LIU) project is charged with planning marked by excellent peak performance, and executing wide-ranging upgrades to good availability and operational flexibility the complex to meet these requirements. The US Department of Energy (DOE) Photomultiplier tubes surrounded by (CERN Courier December 2016 p5). Both the LIU and HL-LHC projects have has formally approved a key construction LBNL polytetrafluoroethylene for the LZ Targeting further improvement, a thorough come through a recent cost-and-schedule milestone for the LUX-ZEPLIN (LZ) experiment, which is managed by Lawrence review of LHC operation and system review, and at present are fully funded and experiment, propelling the project towards Berkeley National Laboratory. performance was the focus of discussions on schedule. The injector upgrades will be its April 2020 goal for completion. On in the first phase of the annual LHC Beam is due back in the LHC in May. deployed during Long Shutdown 2 (LS2) in 9 February the project passed a DOE review Portugal, Russia and Korea. The detector is performance workshop, which took place 2019/2020, while the HL-LHC will see the and approval stage known as “Critical expected to be at least 50 times more sensitive from 23 to 26 January in Chamonix, France. luminosity target for ATLAS and CMS major part of its upgrades implemented in Decision 3”, which accepts the final design to finding signals from dark-matter particles Experts from the accelerator sector, CERN is 45 fb–1. LS3, which is due to start in 2024. and formally launches construction. The LZ than its predecessor LUX, and will compete management and members of the CERN One open question about future LHC With only two more years of operation detector, which will be built roughly 1.5 km with other liquid-xenon experiments under Machine Advisory Committee explored operations concerns the increase of the before the next long shutdown, planning for underground at the Sanford Underground development worldwide in the race to detect the operational scenarios for the remainder beam energy from 6.5 to 7 TeV per beam, LS2 is already well advanced. For the LHC Research Facility in South Dakota and dark matter. A planned upgrade to the current of Run 2 and made preliminary decisions which would see the machine reach its itself, LS2 will not require the same level of be filled with 10 tonnes of liquid xenon XENON1T experiment (called XENONnT) regarding optics and machine parameters. design specification. To gain input on intervention as seen in LS1. Nonetheless, to detect dark-matter interactions, is at Gran Sasso National Laboratory in Italy Beam is due back in the LHC this year at the high-field magnet behaviour, a dipole here is still a major amount of work planned considered one of the best bets to determine and China’s plans to advance the PandaX-II beginning of May, and the rest of the year will training campaign was conducted at the across the complex including major whether dark-matter candidates known as detector, for instance, are both expected to essentially be dedicated to proton–proton start of the year-end technical stop (CERN upgrades to the injectors in the framework WIMPs exist. have a similar schedule and scale to LZ. physics, with the usual mix of machine Courier March 2017 p9). Experience from of LIU, and significant upgrades to the LHC The project stems from the merger of The LZ collaboration plans to release a development and special physics runs. By this and previous training campaigns was experiments. two previous experiments: LUX (Large Technical Design Report later this year. quantifying the limitations to peak luminosity reviewed and the duration, timing and The exploitation of the LHC and the Underground Xenon) and ZEPLIN (ZonEd “We will try to go as fast as we can to have from electron-cloud effects, the cryogenics associated risks of pushing up to 7 TeV – injector complex has been impressive Proportional scintillation in LIquid Noble everything completed by April 2020,” says system and other factors, luminosity estimates including implications for other accelerator recently, but work across the Organization gases). It was first approved in 2014 and LZ project director Murdock Gilchriese. for the coming years were also drawn up: systems, such as the LHC beam dump – continues unabated in the push to get the currently has about 250 participating “We got a very strong endorsement to go fast in 2017, the peak luminosity should be at were explored. There will be no change of best out of the LHC in both the medium and scientists in 37 institutions in the US, UK, and to be first.” least 1.7 × 1034 cm–2 s–1 and the integrated beam energy in 2017 and 2018. The goal is long term.

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L H C experiments CMS undergoes tracker transplant ATLAS reveals more strangeness in the proton

The excellent Standard Model at the sub-per-cent level. theoretical Q2 = 1.9 GeV 2, x = 0.023 ATLAS The combined electron and muon data, understanding of ABM12 including the correlations of systematic NNPDF3.0 the production MMHT14 uncertainties, were compared to predictions M Brice/CERN of electroweak W and Z gauge bosons in CT14 performed at next-to-next-to leading order proton–proton collisions at the LHC makes ATLAS-epWZ12 (NNLO) in QCD and next-to-leading ATLAS-epWZ16 these “standard-candle” processes ideal exp uncertainty order in electroweak theory. Using for studying the detailed performance of exp+mod+par uncertainty various parton distribution functions, exp+mod+par+thy uncertainty the ATLAS detector, and thus improves the the comparisons revealed significant precision on measurements. Specifically, 0 0.2 0.4 0.6 0.81.0 1.21.4 tensions between measurement and theory. + – differences in the couplings of the W , W , Rs Interpreting HERA-inclusive deep- Z and γ* bosons to quarks and antiquarks inelastic-scattering data including the appear as differences in rapidity distributions Comparison of the ATLAS strangeness ATLAS data in an NNLO QCD fit pointed that reveal additional information about the suppression factor Rs with various to a new sensitivity to the strangeness – – _ structure of the proton. predictions at the point of maximum suppression factor Rs = (s + s)/(d + u), as Protons are often considered to be sensitivity (corresponding to a scale of shown in the figure. The data confirm composed of two up quarks and one down Q2 = 1.9 GeV2 and a proton momentum with significantly improved precision the quark, but when probed at small distances fraction of quarks of x = 0.023). previous ATLAS determination of an they reveal additional content. This includes unsuppressed strange-quark content (shown a “sea” of up and down quarks, strange of charm quarks were detected. Contrary to as ATLAS-epWZ12) based on 2010 data. quarks from the heavier second generation of theoretical expectations, these data revealed The result may have important particles, and the gluons that bind the quarks a suppression of strange quarks relative to the implications for further precision together into the proton. up and down quarks. measurements of Standard Model The ATLAS collaboration has now shed Gaining further insight into the proton parameters, in particular the mass of the light on the least-known component of structure using inclusive W and Z boson W boson and the weak-mixing angle, since the proton – its content of strange quarks production required significant experimental these are affected by the second generation – based on sub-per-cent measurements of improvements, with painstaking calibration of quarks. The ATLAS measurement the kinematic dependencies of the W and efforts revealing detection efficiencies in challenges the current paradigm of a Z boson cross-sections using LHC data real and simulated data at the per-mille level suppression of the strange- compared to recorded in 2011 at an energy of 7 TeV. using both the electron and muon channels. other light-quark distributions, but the quest Previous determinations of the strange-quark Indeed, thanks to these studies, the ATLAS continues. content of the proton were based on neutrino data provided a new test of electron–muon scattering, in which charged-current universality in the weak-interaction sector ● Further reading interaction muons from the fragmentation that is in excellent agreement with the ATLAS Collaboration 2016 arXiv:1612.03016. (Above and below) The new silicon pixel tracker being installed in the central region of the CMS detector.

Hydro ALICE Pb–Pb 2.76 TeV M Brice/CERN Brice/CERN M PHENIX Au–Au 200 GeV collaboration has recently measured the 0.2 < k T < 0.3 GeV/c k0.2 < k0.2 < 2.0 GeV/c 0.3 < k < 0.4 GeV/c At the beginning of March, ALICE measures T T shape of the fireball at freeze-out. 0.4 < k < 0.5 GeV/c 0.2 STAR Au–Au 200 GeV T 0.5 < k T < 0.7 GeV/c the CMS collaboration < k0.15 T < 0.6 GeV/c In a non-central collision, the nuclear ε ε successfully replaced the shape of the QGP init = final overlap region is almond shaped with heart of its detector: the pixel the longer axis oriented perpendicular to final 0.1 tracker. This innermost layer fireball at freeze-out ε the reaction plane (defined by the impact of the CMS detector, a cylindrical device parameter and the beam direction). The containing 124 million sensitive silicon 0 spatial anisotropies in the initial state sensors that record the trajectories of charged Heavy-ion collisions at LHC are converted, via pressure gradients, particles, is the first to be encountered by energies create a hot and dense 0 0.1 0.2 0.3 0.4 to momentum anisotropies, leading to ε debris from the LHC’s collisions. medium of deconfined quarks init anisotropic particle flow. The magnitudes of The original three-layer 64 Mpix tracker, and gluons, known as the Freeze-out eccentricity measured for the momentum anisotropies are quantified by which has been in place since the LHC quark–gluon plasma (QGP). The different ranges of pair transverse the so-called vn coefficients, where the second started operations in 2008, was designed QGP fireball first expands, cools and then momentum as a function of initial-state harmonic coefficient (v2) is generated from the for a lower collision rate than the LHC will freezes out into a collection of final-state eccentricity obtained from Monte Carlo system’s approximately elliptic shape. This is deliver in the coming years. Its replacement hadrons. Correlations between the free models for six centrality ranges, 0–5%, usually called elliptic flow, and the direction contains an additional layer and has its particles carry information about the 5–10%, 10–20%, 20–30 %, 30–40 % and of the strongest component of elliptic flow is first layer placed closer to the interaction space–time extent of the emitting source, 40–50%. defined as the elliptic-flow plane. point. This will enable CMS to cope with The new pixel detector will also be better After a week of intense activity, and a and are imprinted on the final-state spectra The HBT radius, measured as a function the harsher collision environment of future at pinpointing where individual collisions few frayed nerves, the new subdetector was due to a quantum-mechanical interference and Twiss (HBT) interferometry, a technique of the pair-emission azimuth relative to the LHC runs, for which the detector has to occurred and will therefore enhance the safely in place by 8 March. After testing is effect. To measure these correlations and to first used in astronomy for determining the elliptic-flow plane, exhibits oscillations and

simultaneously handle the products from precision with which predictions of the complete, CMS will be closed ready for the determine the space–time parameters of the angular sizes of stars. Using azimuthally thus provides information on the eccentricitys a large number of simultaneous collisions. Standard Model can be tested. LHC to return to action in May. source, physicists utilise Hanbury Brown differential HBT interferometry, the ALICE of the source at freeze-out, when the

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particles cease to interact. The source direction. The freeze-out eccentricities that even after a stronger expansion in particular, the BaBar limits exclude values of 10–2 Regions of the dark-photon eccentricity at freeze-out can be estimated measured by ALICE are smaller than the in-plane direction, the pion source the Aʹ coupling suggested by the dark-photon K → πνν parameter space (mixing from oscillations of the HBT radius at low those measured at RHIC energies, likely at freeze-out is still elongated in the interpretation of the muon g-2 anomaly, strength versus mass) pion-pair transverse momentum. ALICE has reflecting the longer lifetime of the system out-of-plane direction. In the future, the as well as a broad range of parameters for excluded by BaBar (green)

measured the pion HBT-radius oscillations at the LHC. Hydrodynamic calculations ALICE collaboration intends to measure dark-sector models (see figure). (g-2)μ ± 5␴ compared with the previous for different transverse-momentum ranges as performed for similar centralities and pair the azimuthal dependence of the HBT “This paper is the final word from BaBar favoured BaBar 2017 constraints. The new 10–3 a function of centrality in lead–lead collisions transverse-momentum ranges as in the radii relative to the higher-harmonic (n ≥ 3) on a search where the dark photon decays ε analysis rules out (g-2) NA64 at an energy of 2.76 TeV per nucleon pair and ALICE experiment show a similar trend, flow planes, which is directly sensitive invisibly,” says BaBar spokesperson Michael e dark-photon coupling as plotted the results as a function of the initial but predict smaller final-source eccentricity to anisotropies in the system’s collective Roney. “But we are continuing to search for the explanation for the eccentricity (see figure on previous page). corresponding to a more spherical source. velocity fields. dark photons and other dark-sector particles muon (g-2) anomaly and

The final eccentricities are significantly The final-state source eccentricity that have visible decay modes.” –4 places stringent constraints ● Further reading 10 below the initial eccentricities due remains positive for all the pair The BaBar result follows another direct –3 –2 –1 on dark-sector models. ALICE Collaboration 2017 arXiv:1702.01612. 10 10 10 1 10 to a larger expansion in the in-plane transverse-momentum ranges, indicating search for sub-GeV dark photons carried out m (GeV) recently by CERN’s NA64 experiment, in A′ which electrons incident on an active target of Caltech, who has worked on dark-photon then can decay. They are more like ‘dark Rare decay puts Standard Model on the spot probe the process e− Z → e− Z Aʹ. Again, no models. “In contrast to massless dark Z bosons’ than dark photons.” evidence for such decays was found, and photons, which are analogous to ordinary NA64 was able to exclude dark photons with photons, this experiment constrains a ● Further reading 0 The decay rate of the Bs Mass fit of dimuon candidates in the a mass less than around 0.1 G eV. slightly different idea of dark force-carrying BaBar Collaboration 2017 arXiv:1702.03327.

) total meson to two muons is 2 LHCb 0 → + – high-purity region of the machine-learning “The thing is, there are dark photons and particles that are associated with a broken NA64 Collaboration 2017 Phys. Rev. Lett. 118 30 Bs μ μ a flagship measurement BDT > 0.5 B0 → μ+μ– algorithm output (top), and decay-time dark photons,” says theorist Sean Carroll symmetry, which therefore get a mass and 011802. combinatorial in flavour physics. It is B → h+h'– distribution of background-subtracted 0 – – + 50 MeV/c 20 B → π (K ) μ ν 0 + – extremely rare and well predicted in the (s) μ Bs → μ μ signal with lifetime fit B0(+) → π0(+) μ+ μ– Standard Model (SM), with a branching 0 → – superimposed (below). Λb p μ νμ Les physiciens des particules du monde entier sont invités à apporter leurs CERN Courier welcomes contributions from the international –9 10 + → + fraction of (3.65±0.23) × 10 . It proceeds Bc J/ψ μ νμ contributions au CERN Courier, en français ou en anglais. Les articles retenus particle-physics community. These can be written in English or French, via a loop diagram that involves the heaviest decay. The Bs meson system has much in candidates/( seront publiés dans la langue d’origine. Si vous souhaitez proposer un article, and will be published in the same language. If you have a suggestion for known particles: the Z and W bosons and the 0 common with that of the K0 meson, in that 5000 5500 6000 faites part de vos suggestions à la rédaction à l’adresse [email protected]. an article, please send proposals to the editor at [email protected]. top quark. Any unknown heavier particles 2 it exhibits a heavier long-lived state and a m + – (MeV/c ) that exist are likely to also contribute to this μ μ lighter shorter-lived state. Only the former decay, which makes it a very sensitive probe is allowed to decay into μ+μ– in the SM, but

– 8 LHCb of physics beyond the SM. After three decades μ that may not be the case in other scenarios. + ) data μ of unsuccessful searches, the observation of 6 effective lifetime fit The contributions of the two states can be → s the decay was first announced in a joint paper 0 disentangled by fitting a single exponential in Nature in 2015 by the CMS and LHCb 4 to the lifetime distribution (figure, below). Company proole collaborations using LHC data from Run 1. 2 The fitted effective lifetime is consistent σ Founded in Italy in 1960, Walter Tosto SpA is a

Recently the LHCb collaboration reported weighted B candidates/(1 ps within 1 with the hypothesis of only the an improved analysis of this decay with 0 heavier state contributing, and within 1.4σ worldwide leading manufacturer of critical, long lead equipment for the Oil & Gas, Petrochemical, Power & data from 2015 and 2016 added to the Run-1 0510 of the opposite. While this result does not yet Respect our clients Decay time (ps) Energy, Food & Pharma markets. sample. Work during the long shutdown tell us anything about new physics, it allows Respect our people 0 → +π– Responsibly grow our business allowed significant improvements to be made Using the well-known decays B K the sensitivity to be extrapolated to larger With more than 600 employees, 8 facilities and its + + –1 in background rejection, which increased and B → J/ψK to calibrate and normalise the data samples. With the 300 fb integrated- Manufacturing of the ITER Vacuum Vessel sectors advanced manufacturing technologies, the 0 + – 0 + – the experiment᾿s sensitivity. The Bs → μ μ efficiencies, the Bs → μ μ branching fraction luminosity target of the LHCb phase-II Company's growth has reached 110 mln € turnover –9 peak is clearly visible in the resulting mass is measured to be (3.0±0.6) × 10 , which is the upgrade, the two states could be disentangled and a production capacity of over 15.000 Tons per plot, with a small bump possibly due to most precise measurement to date. Although at the 5σ level and thus provide a new and year. the B0 meson to its left (see figure, top). consistent with the SM, the experimental important test of the SM. The significance of the former is 7.8σ, precision still has to improve before it matches Walter Tosto designs and manufactures critical items: corresponding to the first observation of this the present theoretical accuracy. ● Further reading Hydrocracking and Hydrotreater reactors, HP Pressure decay by a single experiment. At just 1.6σ, For the first time, LHCb also measured LHCb Collaboration 2017 LHCb-PAPER-2017-001. Vessels, Separators, Columns, HP Heat Exchangers 0 0 + – the B peak is not significant. the effective lifetime of the Bs → μ μ De Bruyn et al. 2012 Phys. Rev. Lett. 109 041801. Coke drums, Waste Heat Boilers. Thanks to its advanced technologies, to its unique equipment and D a r k m a t t e r its consolidated know-how, the company is capable Cases for the JT60-SA international project to manufacture items of high thickness, without any BaBar casts further doubt on dark photons weight or size limitations.

Dark photons, are hypothetical low-mass in cosmic rays reported by the PAMELA e+e– → γ Aʹ. The search was based on the Today, 97% of the Company’s total production value is spin-1 particles that couple to dark matter satellite. Dark photons have also been assumption that the dark photon decays for export. Its activities are carried out in seven but have vanishing couplings with normal invoked as possible explanations to the muon almost entirely to dark-matter particles and workshops in Chieti, a seafront workshop in the Port of Ortona, which is directly connected to the main matter. Such a boson, which may be g-2 anomaly. therefore that no energy would be deposited − international ports and routes, and in the subsidiary associated with a U(1) gauge symmetry Based on single-photon events in 53 fb 1 in the BaBar detector from its decay products. plant Walter Tosto WTB, based in Romania. in the dark sector and mix kinetically of e+e– collision data collected at the PEP-II Finding no evidence for such processes, with the Standard Model photon, offers B factory in SLAC, California, the BaBar the analysis places 90% confidence-level Waldrich Coburg Milling Machine an explanation for puzzling astrophysical collaboration has now completed a thorough upper limits on the coupling strength of Aʹ to observations such as the positron abundance search for these particles (Aʹ) via the process e+e– for dark photons lighter than 8 G eV. I n http://www.waltertosto.it [email protected] follow us

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C o m p i l e d b y J o h n S w a i n , n ortheaStern U n i v e r S i t y Metallic hydrogen claimed

It has long been expected that hydrogen Photos of a microscopic becomes metallic under sufficient pressure, sample of hydrogen and researchers have been edging closer to within a circular gasket its production. Now, Ranga Dias and Isaac at increasing pressures, Silvera of Harvard University in the US report showing the transition that they have finally observed the bizarre from a transparent (left) quantum state. Squeezed in a diamond-anvil to opaque (centre) and cell to a pressure of 495 GPa, hydrogen 205 GPa 415 GPa 495 GPa reflective (right) state. becomes a shiny metal with a plasma frequency of 32.5±2.1 eV at a temperature how diamond is formed at high pressures superconducting at room temperature. of 5.5 K – a transition predicted more than and retains its form under normal conditions. 80 years ago by Wigner and Huntington. The If metastable, it could have applications as ● Further reading metal may be metastable, remaining metallic a rocket fuel far more powerful than liquid R Dias and I Silvera 2017 Science DOI: 10.1126/ when the pressure is removed, similarly to hydrogen and oxygen, and may even be science.aal1579. Light Transport Systems Self-mixing Sensor Time crystals Handsteiner of the Institute for Quantum Human–pig genetics Optics and Quantum information in Vienna A major challenge in radiation-intense We offer a compact laser Time crystals are a new form of and colleagues uses light from distant environments is the signal transfer from diode based sensor for detecting non-equilibrium matter that has periodic The first successful human–animal hybrid astronomical sources to produce the settings. the source to the (often expensive and not a small displacement and measuring the motion even in its ground state. Norman Yao has been created: a mixture of human and The work pushes back the most recent time radiation-hard) detection system. Lens-based vibration with an accuracy of better than of the University of California, Berkeley, pig. Jun Wu of the Salk Institute in the US and that any local-realistic influences could light transport systems suffer from aberrations, 300 nm. This easy-to-use sensor can be easily colleagues built on previous work making misalignment and radiation damage. D-Beam used for many purposes including cryogenic and colleagues have published detailed have produced the observed Bell inequality offers optical fibre based light transport chamber vibration detection or referencing the instructions for how to make them and chimeras from mice and rats, and managed to violation by about 16 orders of magnitude, or systems that can replace conventional displacement of wired or translational stages measure their properties, leading two groups put human cells into developing pig embryos. approximately 600 years. lens-based systems. for diagnostics. Moreover, it can also be used to report experimental realisations: J Zhang The embryos were then inserted into adult for velocity measurements of gas-jets and fluid of the University of Maryland and colleagues pigs, which carried them for three to four ● Further reading Amongst others, we are experienced in the targets. Our sensor provides a reliable, low via a chain of trapped ions, and Soonwon weeks, after which they were removed and J Handsteiner et al. 2017 Phys. Rev. Lett. 118 060401. D-Beam, a new spin-off company from the development, optimisation and experimental cost and robust solution that can be used in studied. Although considered controversial, exploitation of synchrotron radiation-based Choi of Harvard University and colleagues, University of Liverpool and the Cockcroft even the harshest environments. via an ensemble of dipolar-spin impurities in the work demonstrates that human cells Institute in the UK provides a range of profile monitors, novel micro mirror array-based Giant quantum computer beam halo monitors for the measurements with diamond. These are the first materials to break can be made to survive and grow inside of reliable and cost-efficient beam diagnostics high dynamic range, and advanced sensor a host animal, bolstering hopes for better for use at accelerator and clinical facilities, D-Beam offers easy-to-use and user time-translation symmetry in a way that is An ambitious proposal suggests that a giant technologies, such as silicon photomultipliers. ways to make organs without the need for friendly diagnostics for charged particle analogous to the breaking of space-translation quantum computer able to solve currently light sources, and reactors for applications human donors. in research, healthcare, security, beams. This includes custom-build diagnostics symmetry in crystals, opening a new chapter computationally unsolvable problems such environment and manufacturing. Beam Loss Monitors (BLM) for your specific needs. We have a wide range in experimental condensed-matter physics. as factoring large numbers could be built of numerical and analytical tools for modelling based on existing technology. Winfried Beam diagnostics is a highly specialised area Based on Fibres and optimising our products for even the most ● Further reading Hensiger of the University of Sussex in where it takes many years to develop a new challenging projects. We have established S Choi et al. 2016 arXiv:1610.08057v1. D-Beam offers BLMs based on fibres with the UK and colleagues propose a football- sensor technology. The first advantage of a collaborative network with universities, unique features compared to the commonly N Yao et al. 2017 Phys. Rev. Lett. 118 030401. field-sized microwave-coupled trapped-ion D-Beam is the availability of a broad range of research centres and industry partners from used BLMs. The fibre-based BLM gathers the J Zhang et al. 2016 arXiv:1609.08684v1. quantum computer using thousands of cutting edge beam diagnostics solutions that all over the world. are not currently offered by any other company. information from the entire beam line you are hand-sized modules, each containing 2500 interested in, and not only one point. Further information can be found at trapped-ion qubits, which could be joined to Secondly, we have the required skilled experts Cosmic Bell test www.d-beam.co.uk make an arbitrarily large computer. To factor to optimise a given diagnostics technology Due to the large number of monitors necessary to cover all beam modules in latest generation Bell’s inequality, which provides a test of a 2048 bit (617 digit)-long number (a task platform towards your specific applications. Alexandra Alexandrova large scale accelerators, it is desirable to whether a system is quantum or classical, impossible on classical computers today) Email: [email protected] find a solution which minimises also the overall is usually derived on the assumption that would need, including error correction, some Telephone: +44(0)1925 864 430 or costs of the system. The use of optical fibres Custom-designed Radiators +44(0)7449 618 935 there are no correlations between the two billion qubit ions, and the calculation in different configurations allows covering experimenter’s choice of measurement would take around 110 days. Quantum We offer radiators for high current/high larger segments of the machines. This allows Prof. Carsten P. Welsch energy beam applications, as well as highly settings or anything else that could causally The observations raise the possibility of computing might start to develop along lines to find new sources or losses and to protect Email: [email protected] sensitive radiators for low intensity beams affect the outcomes. This leaves open the generating transplantable human tissue. similar to experimental high-energy physics the equipment. Telephone: +44(0)1925-864 352 where a small number of particles need to be possibility that an unknown cause affects with large facilities funded by international Or +44(0)7973 247 982 detected. Our radiators can be used for single Our systems provide a resolution of around both the choice of settings and measurements ● Further reading collaborations. Fax: +44(0)1925 864 037 particle detection as well as for beam loss 10 cm, which gives an accurate determination before each trial – typically as little as Jun Wu et al. 2017 Cell 168 473. monitoring applications. They are based on of the loss position. Due to their intrinsic D-Beam microseconds before in experimental tests. ● Further reading the generation of scintillation and Cherenkov design advantages our systems are Keckwick lane, Daresbury laboratory A new “cosmic Bell test” by Johannes B Leksitch et al. 2017 Sci. Adv. 3 e1601540. radiation in different types of optical fibres completely insensitive to magnetic fields Daresbury, Warrington, WA4 4AD and cutting edge photo detectors. and neutron radiation. United Kingdom 15

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Gravitational lens challenges cosmic expansion mance measurements Low phase noise oscillators are essential in the development, verification . Using galaxies as vast gravitational lenses, agreement with other recent determinations and optimization of every particle accelerator. In a single instrument the Visit us at an international group of astronomers has in the local universe using classical ¸FSWP provides best-in-class noise and jitter sensitivity, ultra-fast made an independent measurement of how cosmic-distance ladder methods. One of measurement speed and the benefit of an internal low phase noise oscillator. IPAC in Copenhagen, fast the universe is expanding. The newly these, by Adam Riess and collaborators, finds measured expansion rate is consistent with an even higher value of the Hubble constant ❙ Superior jitter measurement down to 0.3 Hz offset Booth 46 and 47 –1 –1 earlier findings in the local universe based on (H0 = 73.2±1.7 km s Mpc ) and has therefore ❙ Measurement of additive phase noise at the push of a button more traditional methods, but intriguingly triggered a lot of interest in recent months. ❙ Internal low phase noise oscillator coupled with enhanced cross- ESA/Hubble; NASA, Suyu et al remains higher than the value derived by the The reason is that such values are in correlation functionality Planck satellite – a tension that could hint at tension with the precise determination new physics. of the Hubble constant by the Planck Rohde & Schwarz provides a dedicated portfolio of excellent T&M The rate at which the universe is satellite. Assuming standard “Lambda instruments and power amplifier solutions for development, com- expanding, defined by the Hubble constant, Cold Dark Matter” cosmology, the Planck is one of the fundamental quantities in collaboration derived from the cosmic- missioning, optimization and operation of particle accelerators. cosmology and is usually determined by The Hubble constant was derived by microwave-background radiation a value of –1 –1 techniques that use Cepheid variables studying a gravitational lens called H0 = 67.9±1.5 km s Mpc (CERN Courier and supernovae as points of reference. A HE 0435-1223. The foreground galaxy May 2013 p12). The discrepancy between www.rohde-schwarz.com/ad/particle-accelerators group of astronomers from the H0LiCOW creates four almost evenly distributed Planck’s probe of the early universe and collaboration led by Sherry Suyu of the images of the distant quasar around it. local values of the Hubble constant could Max Planck Institute for Astrophysics be an indication that we are missing a vital in Germany, ASIAA in Taiwan and astronomers can see the different images of ingredient in our current understanding of the Technical University of Munich, the quasar flicker at different times, and the the universe. used gravitational lensing to provide an delays between them depend on the lengths A possible explanation of this discrepancy, independent measurement of this constant. of the paths the light has taken. Deriving according to Riess and colleagues, could The gravitational lens is made of a galaxy the Hubble constant therefore depends on involve an additional source of dark radiation that deforms space–time and hence bends the very precise modelling of the distribution of in the early universe, corresponding to a light travelling from a background quasar, the mass in the lensing galaxy, as well as on significant increase in the effective number which is an extremely luminous and variable several hundred accurate measurements of of neutrino species. It will be interesting galaxy core. This bending results in multiple the multiple images of the quasar to derive its to follow this debate in the coming years, images, as seen from Earth, of the same variability pattern over many years. when new observing facilities and also new quasar that are almost perfectly aligned with This complexity explains why the parallax measurements of Cepheid stars by the lensing galaxy (see image). measurement of the Hubble constant the Gaia satellite will reduce the uncertainty While being simple in theory, in practice – reported in a separate publication by of the Hubble constant determination to a the new technique is rather complex. A H0LiCOW collaborator Vivien Bonvin from per cent or less. straightforward equation relates the Hubble the EPFL in Switzerland and co-workers constant to the length of the deflected light – relies on a total of four papers by the ● Further reading rays between the quasar and Earth. Since H0LiCOW collaboration. The obtained value V Bonvin et al. 2017 MNRAS 465 4914. –1 –1 the brightness of a quasar changes over time, of H 0 = 71.9±2.7 km s Mpc is in excellent A Riess et al. 2016 ApJ 826 56.

Picture of the month

The night sky holds many stunning views, and this is certainly one of them. This pair of galaxies called Arp 142 is better known as the Porpoise Galaxy, although it rather looks like a penguin guarding its egg. Reprocessed recently, this image by the Hubble Space Telescope reveals in magnificent detail the strange shape of a former normal spiral galaxy (NGC 2936, on top) now stretched and twisted by the gravitational force of its elliptical companion (NGC 2937, below). The blue skin of the “penguin” comes from massive, young and hot stars recently formed by gas compression due to the gravitation interaction. On the contrary, the white colour of the “egg” means that there is currently very little gas and star-forming activity in this galaxy, which is mainly composed of old stars. The brownish dust lines artistically cross near the penguin’s eye, which is the core of the spiral galaxy and likely NASA, ESA, Hubble, HLA; Reprocessing & Copyright: Raul Villaverde R&S®FSWP Phase noise analyzer and VCO tester the last part to be disrupted in the merging process foreseen in about a billion years from now, far away in the Hydra constellation.

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CCApr17_Astrowatch.indd 16 08/03/2017 15:29 21524.001_ParticleAcceleratorFSWP_CERNCourier-April17_213x282_e.indd 1 22.02.17 11:37 Uhr CERNCOURIER www. V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 CERN Courier April 2017 Theory The two-loop explosion

During the past two years there has been a burst of activity in next-to-next-to-leading order calculations to ensure that theory keeps up with the increasing precision of LHC measurements.

Studying matter at the highest energies possible has transformed our understanding of the microscopic world. CERN’s Large Hadron Collider (LHC), which generates proton collisions at the highest energy ever produced in a laboratory (13 TeV), provides a controlled environment in which to search for new phenomena and to address fundamental questions about the nature of the interac- tions between elementary particles. Specifically, the LHC’s main detectors – ATLAS, CMS, LHCb and ALICE – allow us to meas- ure the cross-sections of elementary processes with remarkable precision. A great challenge for theorists is to match the experi- mental precision with accurate theoretical predictions. This is necessary to establish the Higgs sector of the Standard Model of particle physics and to look for deviations that could signal the existence of new particles or forces. Pushing our current capabili- ties further is key to the success of the LHC physics programme. Underpinning the prediction of LHC observables at the highest levels of precision are perturbative computations of cross-sections. Perturbative calculations have been carried out since the early days of quantum electrodynamics (QED) in the 1940s. Here, the small- ness of the QED coupling constant is exploited to allow the expres- sions for physical quantities to be expanded in terms of the coupling constant – giving rise to a series of terms with decreasing magnitude. The first example of such a calculation was the one-loop QED cor- rection to the magnetic moment of the electron, which was carried out by Schwinger in 1948. It demonstrated for the first time that QED was in agreement with the experimental discovery of the anomalous

magnetic moment of the electron, ge-2 (the latter quantity was dubbed “anomalous” precisely because, prior to Schwinger’s calculation, it did not agree with predictions from Dirac’s theory). In 1957, Som- merfeld and Petermann computed the two-loop correction, and it s

Next-to-next-to-leading order (NNLO) Feynman diagrams relevant to the LHC physics programme. (Image credit: Daniel Dominguez, CERN.)

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took another 40 years until, in 1996, Laporta and Remiddi computed 3 3 W/Z total, H total, Harlander, Kilgore analytically the three-loop corrections to ge-2 and, 10 years later, CDF (1995, 2005) H total, Anastasiou, Melnikov VBF total, Bolzoni, Maltoni, Moch, Zaro D0 (1995) 0( ), NLO even the four- and five-loop corrections were computed numerically αs H total, Ravindran, Smith, van Neerven WH diff., Ferrera, Grazzini, Tramontano UA2 (1990) 0(1), LO by Kinoshita et al. The calculation of QED corrections is supple- UA1 (1989) WH total, Brein, Djouadi, Harlander γ-γ, Catani et al. mented with predictions for electroweak and hadronic effects, and H diff., Anastasiou, Melnikov, Petriello 2 2 Hj (partial), Boughezal et al. makes ge-2 one of the best known quantities today. Since ge-2 is also H diff., Anastasiou, Melnikov, Petriello tt– total, Czakon, Fiedler, Mitov measured with remarkable precision, it provides the best determi- W diff., Melnikov, Petriello Z-γ, Grazzini, Kallweit, Rathlev, Torre W/Z diff., Melnikov, Petriello nation of the fine-structure constant with an error of about 0.25 ppb. jj (partial), Currie, Gehrmann-De Ridder, Glover, Pires

B(W → e ν ) (nb) H diff., Catani, Grazzini

This determination agrees with other determinations, which reach B(Z → ee) (nb) • • ZZ, Cascioli et al.

Z W 1 1 W/Z diff., Catani et al. ␴ an accuracy of 0.66 ppb, showcasing the remarkable success of quan- ␴ ZH diff., Ferrera, Grazzini, Tramontano 1 tum field theory in describing material reality. WW, Gehrmann et al. In the case of proton–proton collisions at the LHC, the dominant tt– diff., Czakon, Fiedler, Mitov processes involve quantum chromodynamics (QCD). Although in Z-γ, W-γ, Grazzini, Kallweit, Rathlev general the calculations are more complex than in QED due to 0 0 Hj, Boughezal et al. 12 12 Wj, Boughezal, Focke, Liu, Petriello the non-abelian nature of this interaction, i.e. the self-coupling of √s (TeV) √s (TeV) Hj, Boughezal et al. gluons, the fact that the QCD coupling constant is small at the high VBF diff., Cacciari et al. energies relevant to the LHC means that perturbative methods are Fig. 1. Comparison of inclusive W-production (left) and Zj, Gehrmann-De Ridder et al. ZZ, Grazzini, Kallweit, Rathlev possible. In practice, all of the Feynman diagrams that correspond Z-production (right) data with leading-order (blue) and NLO 2002 2004 2006 2008 2010 2012 2014 2016 Hj, Caola, Melnikov, Schulze to the lowest-order process are drawn by considering all possible (red, with uncertainty in pink) predictions. Zj, Boughezal et al. ways in which a given final state can be produced. For instance, in WH diff, ZH diff., Campbell, Ellis, Williams the case of Drell–Yan production at the LHC, the only lowest-order are required to describe Drell–Yan data, and marked the first great γ-γ, Campbell, Ellis, Li, Williams WZ, Grazzini, Kallweit, Rathlev, Wiesemann diagram involves an incoming quark and an incoming antiquark success of perturbative QCD (figure 1). WW, Grazzzini et al. * from the proton beams, which annihilate to produce a Z, γ or a Things have changed a lot since then. Today, NLO corrections MCFM at NNLO, Boughezal et al.

W boson, which then decays into leptons. Using the Feynman r ules, have been calculated for a large class of processes relevant to the PtZ, Gehrmann-De Ridder et al. such pictorial descriptions can be turned into quantum-mechanical LHC programme, and several tools have been developed to even amplitudes. The cross-section can then be computed as the square compute them in a fully automated way. As a result, the problem of Fig. 2. The completion date and main authors of various NNLO calculations, with vertical separations for display purposes. of the amplitude, integrated over the phase space and appropriately NLO QCD calculations is considered solved and comparing these summing and averaging over quantum numbers. to data has become standard in current LHC data analysis. Thanks all calculations were essentially limited to “2 → 1” scattering pro- ferential equations can be organised in a simple form that makes This lowest-order description is very crude, however, since it to the impressive precision now being attained by the LHC experi- cesses, in essence Higgs andexplosion Drell–Yan of calculations production, in theas well past as 18 Higgs months finding solutions, i.e. finding expressions for the wanted two-loop does not account for the fact that quarks tend to radiate gluons. To ments, however, we are now being taken into the complex realm of production in association with a Drell–Yan pair. From a QCD point integrals, a manageable problem. Practically, the set of multi- incorporate such higher-order quantum corrections, next-to-leading higher-order calculations. of view, the latter process is simply off-shell Drell–Yan production loop integrals to be computed can be regarded as a set of vectors. order (NLO) calculations that describe the radiation of one addi- in which the vector boson radiates a Higgs. A few 2 → 2 calculations Decomposing these vectors in a convenient set of basis vectors can tional gluon are required. This gluon can either be real, giving rise The NNLO explosion started to appear in 2012, most notably top-pair production and the lead to significant simplifications of the differential equations, and to a particle that is recorded by a detector, or virtual, corresponding The new frontier in perturbative QCD is the calculation of next- production of a pair of vector bosons. It is only in the past two years, concrete criteria were proposed for finding an optimal basis. The to a quantum-mechanical fluctuation that is emitted and reabsorbed. to-next-to-leading order (NNLO) corrections. At the level of dia- however, that we have witnessed an explosion of NNLO calcula- very important NNLO calculations of diboson production have Both contributions are divergent because they become infinite in the grams, the picture is once again pretty simple: at NNLO level, it tions (figure 2). Today, all 2 → 2 Standard Model LHC scattering benefitted from this technology. limit when the energy of the gluon is infinitesimally small, or when is not just one extra particle emission but two extra emissions that processes are known to NNLO, thanks to remarkable progress in Currently, when only virtual massless particles are involved and the gluon is exactly collinear to one of the emitting quarks. When are accounted for. These emissions can be two real par tons (quarks the calculation of two-loop integrals and in the development of pro- up to a total of four external particles are considered, the two-loop real and virtual corrections are combined, however, these diver- or gluons), a real parton and a virtual one, or two virtual partons. cedures to handle intermediate divergences. integral problem is considered solved, or at least solvable. How- gences cancel out. This is a consequence of the so-called Kinoshita– The first NNLO computation for a collider process concerned Compared to NLO calculations, NNLO calculations are substan- ever, when massive particles circulate in the loop, as is the case for Lee–Nauenberg theorem, which states that low-energy (infrared) “inclusive” Drell–Yan production, by Hamberg, Van Neerven and tially more complex. Two main difficulties must be faced: loop inte- a number of LHC processes, the integrals give rise to a new class divergences must cancel in physical (measurable) quantities. Matsuura in 1991. Motivated by the SPS and Tevatron data, and also grals and divergences. Two-loop integrals have been calculated in of functions, elliptic functions, and it is not yet understood how to Even if divergences cancel in the final result, a procedure to han- by the planned LHC and SSC experiments, this was a pioneering the past by explicitly performing the multi-dimensional integration, solve the associated differential equations. Hence, for processes dle divergences in intermediate steps of the calculations is still calculation that was performed analytically. The second NNLO cal- in which each loop gives rise to a “D-dimensional” integration. For with internal masses we still face a conceptual bottleneck. Over- needed. How to do this at the level of NLO corrections has been culation, in 2002, was for inclusive Higgs production in gluon–gluon simple cases, analytical expressions can be found, but in many cases coming this will be very important for Higgs studies at large trans- well understood for a number of years. The first successes of NLO fusion by Harlander and Kilgore. Inclusive calculations refer only to only numerical results can be obtained for these integrals. The com- verse momentum, where the top loop to which the Higgs couples QCD calculations came in the 1990s with the comparison of Drell– the total cross-section for producing a Higgs boson or a Drell–Yan plexity increases with the number of dimensions (i.e. the number of is resolved. The calculation of these integrals is today an area with Yan particle-production data pair without any restriction on where these particles end up, which is loops) and with the number of Lorentz-invariant scales involved in tight connections to more formal and mathematical areas, leading recorded by CERN’s SPS and not measurable because detectors do not cover the entire phase space the process (i.e. the number of particles involved, and in particular to close collaborations between the high-energy physics and the Fermilab’s Tevatron experi- such as the region close to the beam. the number of massive particles). mathematical/formal-oriented communities. Compared to NLO ments to leading-order and NLO The first “exclusive” NNLO calculations, which allow kinematic Recently, new approaches to these loop integrals have been sug- The second main difficulty in NNLO calculations is that, as calculations, NNLO QCD predictions, which had cuts to be applied to the final state, started to appear in 2004 for gested. In particular, it has been known since the late 1990s that at NLO, individual contributions are divergent in the infrared are substantially first been computed in 1979 by Drell–Yan and Higgs production. These calculations were motivated integrals can be treated as variables entering a set of differential region, i.e. when particles have a very small momentum or become Altarelli, Ellis and Martinelli. by the need to predict quantities that can be directly measured, rather equations, but solutions to those equations remained complicated collinear with respect to one another, and the structure of these more complex. The comparison revealed une- then relying on extrapolations to describe the effects of experimental and could be found only on a case-by-case basis. A revolution singularities is now considerably more complex because of the s quivocally that NLO corrections cuts. The years 2004–2011 saw more activity, but limited progress: came about just three years ago when it was realised that the dif- extra particle radiated at NNLO. All singularities cancel when

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179 we should also ask if it is worth the effort. A comparison with data

61 MATRIX ␴(pp → WZ)

7 for the diboson (WZ) production process at different LHC beam B energies to NLO and NNLO calculations (figure 3) provides an Looin orard to ATLAS 7 TeV 66 GeV < m(Z) < 116 GeV indication of the answer. It is clear that LHC data already indicate Phys. Lett. a clear preference for NNLO QCD predictions and that, once more CMS 7 TeV 71 GeV < m(Z) < 111 GeV data are accumulated, NLO will likely be insufficient. While it is early days for NNLO phenomenology, the same conclusion applies ATLAS 8 TeV 66 GeV < m(Z) < 116 GeV to other measurements examined so far. photonphoton physics CMS 8 TeV 71 GeV < m(Z) < 111 GeV In the past, accurate precision measurements have provided a strong motivation to push the precision of theoretical predictions. On CMS 13 TeV 60 GeV < m(Z) < 120 GeV the other side, very precise theory predictions have stimulated even as quoted by ATLAS more precise measurements. Today, the accuracy reached by LHC ATLAS 13 TeV in arXiv: 1606.04017 measurements is by far better than what anybody could have pre- reo eroeer e o eher e DATA/NNLOref NNLO/NNLOref dicted when the LHC was designed. For instance, the Z transverse DATA/NLO ref NLO/NLOref momentum spectrum reaches an accuracy of better than a per cent o he eere roe he over a large range of transverse momentum values, which will be 1.21.00.80.60.40.20 1.4 1.6 1.8 2.0 important to further constrain parton-distribution functions, and the r o o eeroe oo data/theory mass of the W boson, which enters precision tests of the Standard oher o e hy Fig. 3. Comparison of LHC data for the WZ production Model, is measured with better than 20 MeV accuracy. In the future, cross-section versus NLO (magenta) and NNLO QCD (blue) one should expect that high-precision theoretical predictions will predictions. push the experimental precision beyond today’s foreseeable bounda- ries. This will usher in the next phase in perturbative QCD calcula- s its name suggests, the Large Hadron Collider LHC at CER all contributions are combined, but to have exclusive predictions it tions: next-to-next-to-next-to-leading order, or N3LO. smashes hadrons into one another – protons, to be precise The is necessary to cancel the singularities before performing integra- Today we have two pioneering calculations beyond NNLO: the energy from these collisions gets converted into matter, produc- tions over the phase space. Compared to NLO, where systematic N3LO calculation of inclusive Higgs production (in the large top- ing ne particles that allo us to explore matter at the smallest ways to treat these intermediate divergences have been known for mass approximation), and the N3LO calculation of inclusive vector- scales. The LHC does not fi re protons into one another individu- many years, the problem is more difficult at NNLO because there boson-fusion Higgs production. Both calculations are inclusive over ally instead, they are circulated in approximately 2000 bunches are more divergent configurations and different divergences over- radiation, exactly in the same way that the first NNLO calculations each containing around 100 billion protons hen to bunches are lap. The past few years have seen remarkable developments in the were. These calculations are now suggestive of a good convergence focused magnetically to cross each other in the centre of detectors understanding and treatment of infrared singularities in NNLO of the perturbative expansion, meaning that the N3LO correction is such as C and TL, only 0 or so protons actually collide computations of cross-sections, and a range of methods based on very small and that the N3LO result lies well within the theoretical The rest continue to fl y through the LHC unimpeded until the next different physical ideas have been successfully applied. uncertainty band of the NNLO result. Turning these calculations time that to bunches cross into fully exclusive predictions is the next theoretical challenge. ccasionally, something very different happens If to protons rtistic view of the Beyond NNLO travelling in opposite directions pass very close to one another, C- detectors m from the C Is the field of precision calculations close to coming to an end? ● Further reading photons radiated from each proton can collide and produce ne detector, showing the silicon piels inside the oman pots. The answer is, of course, no. First, while the problem of cancel- T Aoyama et al. 2012 Phys. Rev. Lett. 109 111807. particles The to parent protons remain completely intact, con- (mage credit ergio Cittolin.) ling singularities is in principle solved in a generic way, in prac- T Becher 2016 arXiv:1607.01165. tinuing their path in the LHC, but the photon–photon interaction tice all methods have been applied to 2 → 2 processes only, and no C Duhr 2014 arXiv:1411.7538. removes a fraction of their initial energy and causes them to be being developed by TL, and both experiments aim to be in oper- 2 → 3 cross-section calculation is foreseen in the near future. For J M Henn 2013 Phys. Rev. Lett. 110 251601. slightly defl ected from their original trajectories. By identifying ation throughout this years LHC proton–proton run instance, the very important processes of three-jet production or M Passera 2005 J. Phys. G 31 R75. the defl ected protons, one can determine whether such photon Higgs production in association with a top-quark pair are known interactions took place and effectively turn the LHC into a photon Liht collisions to NLO accuracy only. Similarly, two-loop pentagon integrals Résumé collider It is also possible for the to protons to exchange pairs of Despite photons being electrically neutral, the tandard odel required for the calculation of 2 → 3 scatterings are at the fron- L’explosion des doubles boucles gluons, hich is another interesting process allos to photons to interact via the exchange of virtual charged tier of what can be done today. Furthermore, most of the existing The idea of tagging defl ected protons has been pursued at previ- par ticles. Several fi nal states are possible (fi gure 1, overleaf ), includ- NNLO computer codes require extremely long runs on large com- Ces deux dernières années, l’univers des calculs de l’ordre ous colliders, and also at the LHC back in 2012 and 201 using only ing a pair of photons The latter process γγ → γγ, or light-by-light puter farms, with typical run times of several CPU years. It could sous-sous-dominant (NNLO) a connu une activité frénétique, qui lo-intensity beams The proposal to pursue this type of physics scattering has been knon since the development of uantum elec- be argued that this is not an issue in an age of large computer farms visait à permettre à la théorie de tenir le rythme des expériences. with the LHC’s CMS and/or ATLAS experiments was fi rst pre- trodynamics QED and tested indirectly in several experiments, but and parallel processing and when CPU time is expected to become Les prédictions sur les observations du LHC s’appuient sur des sented many years ago, but the project (under the name FP420) did the fi rst direct evidence came last year from ATLAS in low-luminos- cheaper over the years, however, the number of phenomenological calculs perturbatifs des sections efficaces, et les corrections not materialise ity measurements of lead–lead collisions CN Courier Decem- studies that can be done with a theory prediction is much larger NLO ont déjà été calculées pour une grande partie des processus A new project called the CMS-TOTEM Precision Proton Spec- ber 2016 p9 ince the probability of emitting photons scales ith when calculations can be performed quickly on a single machine. pertinents pour le programme du LHC. Or, étant donné la précision trometer (CT-PPS) has now taken up the challenge of making pho- the suare of the electrical charge, the cross-section for lead–lead Hence, in the coming years NNLO calculations will be scrutinised impressionnante qu’atteignent à présent les expériences LHC, nous ton–photon physics possible at the LHC hen operating at nominal collisions is signifi cantly higher than for proton–proton collisions. and compared in terms of their performances. Ultimately, only one nous retrouvons maintenant dans le royaume complexe des calculs luminosity hile C is a general-purpose detector for LHC phys- By searching for two photons and nothing else in the central detec- or a few of the many existing methods to perform integrals and to d’ordre plus élevé, où l’activité a explosé ces derniers mois. ics, CT-PPS uses two sets of detectors placed 200 m either side of tor and using kinematics cut to suppress backgrounds, the invariant treat intermediate divergences is likely to take over. the C interaction point to measure protons in the forard direc- mass of the to photons as in the region of 10 e The measured ▲ Given how hard and time-consuming NNLO calculations are, Giulia Zanderighi, CERN and University of Oxford. tion. A parallel project called ATLAS Forward Physics (AFP) is also cross-section as compatible ith the QED prediction and, since

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CT-PPS CT-PPS CT-PPS p p p p timing tracking 2 tracking 1

* γ – * – l γ W

+ γ * + γ * l W

pp pp

Fig. 1. The interaction between two photons can produce a lepton pair of opposite charge (left), while light-by-light scattering (middle) involves a loop of virtual charged particles and therefore the corresponding cross-section is very low. Two photons may also interact with two W bosons in a quartic vertex (right), which is a four-point interaction. The white circle suggests the interesting possibility that this interaction involves new particles of high mass or new couplings. (Left) CT-PPS detectors installed in the LHC tunnel (CMS lies 200 m to the right). (Middle) Roman Pot upgraded with special RF shields for operation at high-luminosity. (Right) The new CT-PPS no deviations are expected in this low-mass range, the ATLAS result Forward thinking tracking detector package using 3D pixels to be used in 2017. The box at the bottom, containing six was interesting but somewhat expected. Given their potential for revealing new physics, photon–photon planes of silicon pixels, is inserted in the RP and the RP is mounted in a mechanical structure in In forward experiments such as CT-PPS and AFP, however, the collisions have been a topic of some interest for many decades. For the beamline that can be moved towards the beam. high-luminosity proton collisions allow a much higher mass region example, photon–photon collisions were studied at CERN’s Large to be probed – between 300 GeV and 2 TeV in the case of CT-PPS. Electron Positron (LEP), while studies at DESY’s HERA and Fer- few millimetres from the LHC’s high-intensity beams. The final difference of the time-of-arrival to the two protons, so that it can Proton tagging is possible because centrally produced high-mass milab’s Tevatron colliders concentrated on interactions of protons demonstration happened between April and May 2016, and the reject the background from spurious collisions piling up in the systems cause the protons to lose enough energy to be deflected through the exchange of gluons to probe quantum chromodynamics green light for CT-PPS operation in regular high-luminosity LHC same bunch crossing. A time precision of 20 ps makes it possible to into the CT-PPS detectors. The study of photon interactions in this in the non-perturbative regime. The LHC achieves a much higher running was given the following month. estimate the z-vertex with the 3 mm accuracy needed to reduce the region could therefore provide new insights about the electroweak energy and luminosity than LEP, but at the price of colliding parti- background sufficiently. The timing detectors had used diamond interaction, in particular the quartic gauge couplings predicted by cles that are not elementary. Therefore, the elementary interactions Success so far sensors in 2016 and will add silicon low-gain avalanche diodes the SM. These are interactions where two photons annihilate upon between gluons and quarks do not have well-defined energies and The CT-PPS project redesigned the RPs to suit these harsh oper- this year. Again, the experience acquired in a high-rate and high- collision to produce two W bosons, implying four particles at the the interaction products include the remnants of the two protons, ating conditions. In collaboration with LHC teams, they also radiation environment will be most valuable for CMS upgrades same vertex in a Feynman diagram (figure 1). Deviations from the making physics analyses more difficult in general. conducted a thorough programme of RP insertions at increas- for HL-LHC. SM prediction would point to new physics in the same way as the Proton-tagged photon collisions at the LHC, on the other hand, ingly closer distances to the beam, measuring its impact on beam Meanwhile, the ATLAS collaboration installed one arm of the observations of deviations from the quartic coupling in Fermi’s are very clean. Since photons are elementary particles and there monitors. Great care must be taken not to disrupt the beam, since AFP experiment in early 2016 and has taken data in special low- beta-decay theory in the 1930s were the forerunner to the discov- are no proton remnants, the photon–photon collision energy at the if the protons start to scrape the RPs there would be an increase luminosity runs to study diffraction. The second AFP arm, with ery of the W boson 50 years later. LHC is precisely defined by the kinematics of the two tagged pro- in secondary particles that would trigger a beam dump. In 2016, horizontal RP stations similar to those of CT-PPS, has also since If there are new particles with masses above 300 GeV, CT- tons. In conjunction with CT-PPS, CMS can therefore probe anom- CT-PPS used non-final detectors to collect 15.2 fb–1 of data inte- been installed and its four-layer 3D silicon pixel detectors and new PPS could also improve CMS’s general discovery potential. For alous quartic couplings with much better sensitivity than before. grated in the CMS data set. CT-PPS has proven for the first time Cherenkov-based time-of-flight detectors are being assembled. example, diphoton resonances at high mass have a very clean The physics we are interested in corresponds to the process the feasibility of operating a near-beam proton spectrometer at They will be installed and commissioned before the LHC restarts signature almost free of any background. Thus, in addition to pp → ppX, where the “pp” part is measured by the CT-PPS high luminosity on a regular basis and has paved the way for other in May this year. Like CT-PPS, AFP aims to participate in high- precision electroweak tests, forward experiments such as CT- detectors and the system “X” is measured in the other CMS sub- such spectrometers. luminosity running throughout the year, with both operating in PPS provide an important cross-check of “bumps” in invari- detectors. In the case of the quartic coupling γγWW, for instance, CT-PPS is also facing big challenges in the development of the tandem to enhance the LHC’s search for new physics. ant mass distributions by offering complementary information the process is pp → ppWW. The two photons that merge into two final detectors. The tracking detectors have a surface area of just about the production mechanism, coupling and quantum num- W are not measured directly, but energy-momentum conserva- 2 cm2 and reside in two RPs located 10 m apart on either side of the Résumé bers of a possible new resonance. An example of this comple- tion allows all of the kinematic properties of the WW pair to be collision point (for a total of four stations). Six planes of silicon La physique des collisions de photons bientôt d’actualité mentarity concerns the now-infamous 750 GeV bump in the deduced much more precisely from the CT-PPS proton measure- pixels on each station will detect the track of the flying protons to diphoton invariant-mass distributions from the LHC’s 2015 data ments than could be achieved from the measurements of W decay provide direction information, and the magnetic field of the LHC’s Le LHC fait normalement entrer en collision des protons avec set. Although the bump turned products with the CMS detector alone. magnets will serve as the proton-deflecting field. The devices d’autres protons. Or, si deux protons circulant dans des sens out to be a statistical effect, it The CT-PPS detectors are located on either side of CMS, 200 m themselves have to sustain exceedingly high radiation fluxes given opposés passent très près l’un de l’autre, les photons alors émis provided strong motivation to from the interaction point. They rely on objects called Roman their proximity to the beam: a proton fluence in excess of 5 × 1015 par chacun des protons peuvent entrer en collision et produire Photon–photon advance the CT-PPS physics Pots (RP), which are cylinders that allow small detectors to be particles/cm2 is expected after an integrated luminosity of 100 fb–1. de nouvelles particules. Des spectromètres de précision situés en collisions have been programme at the time. Were moved into the LHC beam pipe so that they sit a mere few mm CMS’s own tracker will not face these radiation conditions until the amont et en aval de l’expérience CMS et un projet semblable en a topic of some similar bumps to be observed from the beam. The RPs of TOTEM are designed to operate HL-LHC enters operation in the mid 2020s. cours de réalisation auprès d’ATLAS enregistreront ces événements by CMS and ATLAS in future, under special LHC runs with a small number of collisions per From 2017 onwards, CT-PPS will be using new 3D pixel tech- afin de partir en quête des couplages quartiques des bosons interest for many CT-PPS and AFP will play an second. However, the physics goals of CT-PPS require the RPs nology that has been developed in view of upgrades to the CMS électrofaibles et d’autres signes d’une nouvelle physique. Les deux decades. important role in determin- to operate during normal CMS data-taking, when the LHC pro- tracker and therefore provide valuable experience with the new dispositifs seront installés et mis en service avant le redémarrage du ing whether a real resonance vides a much higher number of collisions per second. The first sensors. The project also relies on high-precision timing detec- LHC au mois de mai prochain. is responsible for the excesses and most important goal of the CT-PPS project was therefore to tors. CT-PPS matches the primary vertex of the collision measured seen in the data. demonstrate that the detectors could operate successfully only a in the central detector with the vertex position obtained from the Achintya Rao, UWE Bristol, and Joao Varela, L I P.

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103 Thirty years in detection: the collision PbPb √s = 2.76 TeV of a 200 GeV/nucleon sulphur ion on a 102 NN

CERN EX-38-7-91 CERN gold target from the CERN SPS seen by 10 the NA35 streamer chamber in 1986 (image left), and a collision between 1 two lead ions at a nucleon–nucleon 10–1 centre- of-mass energy of 5.02 TeV –2 10 recorded by the LHC’s ALICE yield dN/dy –3 experiment (main image). 10 10–4 data, ALICE, 0–10% 10–5 2 statistical model fit (χ /Ndf = 29.1/18) T = 156.5 MeV, μ = 0.7 MeV, V = 5280 fm3 10–6 B

+ – + – 0 – – – –+ – – + – 3 3––––3 3 4 – π π K K KS φ p p Λ Λ Ξ Ξ Ω Ω d d He He ΛH Λ–H He

During hadronisation of the QGP, final states range from non-strange and strange mesons and baryons to light nuclei. The Three decades since the first ultrarelativistic data were recorded by ALICE in central lead–lead collisions at an energy of 2.76 TeV and fitted with a grand canonical thermal collisions were produced at CERN, the field model with a temperature of 156 MeV.

of heavy-ion physics could be about to enter experiments dedicated to the heavy-ion programme has emerged a new paradigm. the clear picture that a new state of colour-deconfined matter has been created in the early stage of the collision that develops into a collective expansion of the fireball in the later stages. Heavy-ion and proton–proton collisions at ultrarelativistic ener- This finding confirmed a fundamental prediction of QCD: gies provide a unique system with which to investigate the dynam- above a critical temperature, quarks are no longer confined in ics of matter in the early universe. By generating an incredibly hot hadrons. The CERN announcement was, however, only the and dense “fireball” of fundamental par ticles, such collisions allow beginning of our exploration into strongly interacting matter. The us to recreate the extreme conditions of the universe during its first same year, the baton was passed to the Relativistic Heavy Ion tens of microseconds of existence. Collider (RHIC) at Brookhaven National Laboratory in the US. Given that the universe did not become transparent until Just five years after the CERN announcement, the remarkable roughly 370,000 years after the Big Bang, this epoch in our his- data collected at RHIC demonstrated that a change of paradigm tory lies completely out of reach to observational astronomy. for strongly interacting matter was needed. The QGP that had According to the Standard Model of particle physics, the emer- been created in RHIC’s STAR and PHENIX experiments did gence of elementary particles and forces took place via a suc- not have the properties of a perfect gas. Rather, it showed all the cession of symmetry-breaking mechanisms at different energy properties of a perfect liquid: a strongly interacting fluid with scales as the universe expanded and cooled. In the early universe, minimal mean free path. matter was made of freely roaming quarks – which formed the With RHIC continuing to produce data, in 2010 CERN rejoined quark–gluon plasma (QGP) – in addition to leptons and gauge the heavy-ion programme with the newly operational Large bosons. The QGP cooled down until hadrons including bary- universe, they probe fundamental predictions about the strong quarks becomes asymptotically weaker as the distance between Hadron Collider (LHC) and the dedicated heavy-ion experiment ons such as neutrons and protons were formed. Photons contin- nuclear force governed by quantum chromodynamics (QCD). them decreases. But it took three major colliders on both sides ALICE, ATLAS, CMS and, more recently, LHCb. This machine ued interacting with charged particles until most of the matter of the Atlantic to find out what was really going on during these marked a factor 25 jump in collision energy compared with RHIC, became bound in neutral atoms, after which they were set free to Surprises galore extreme initial moments. and its experiments confirmed with unprecedented precision the form today’s cosmic microwave background. We have come a long way from the early belief in the 1970s that The first big result came from CERN in 2000, when it was STAR and PHENIX findings. The LHC also offered new opportu- During the past 30 years, a succession of collider experiments this early phase in the universe, recreated by colliding heavy ions announced that heavy-ion collisions generated by the Super Pro- nities to explore deconfined matter in great detail, with the goal of and impressive theoretical achievements have driven immense at continuously increasing energies, comprised a gas of quarks and ton Synchrotron (SPS) had created a new state of matter. CERN’s understanding how the dynamics of matter emerge from the fun- progress in the field of high-energy heavy-ion physics. Not only do gluons. This is what was expected following asymptotic freedom, then Director-General, Luciano Maiani, worded the discovery as damental properties of the strong interaction and from the quark s these results shed new light on the dynamics of matter in the early a feature of QCD that explains how the interaction between two follows: From the combined data presented by the seven CERN infrastructure of particles. More recently, and surprisingly, LHC

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27.4 pb–1 (5.02 TeV pp) + 404 μb–1 (5.02 TeV PbPb) Herwig Schopper recalled at the November workshop, the 1980s their binding energy. The possibility that nuclei were formed at the 2.0 were not the best time to initiate new projects. The CERN budget phase transition to hadrons, and not later via coalescence, would CMS SPS 17.3 GeV (PbPb) LHC 5.02 TeV (PbPb) 0 was severely cut and the laboratory was very much focused on be an interesting complement to baryogenesis. 1.8 π WA98 (0–7%) CMS (0–5%) arXiv:1611.01664 π± NA49 (0–5%) models 5.02 TeV (PbPb) the construction of the Large Electron–Positron Collider (LEP). Strong future RHIC 200 GeV (AuAu) SCETG (0–10%) Despite this, Schopper bravely decided to give heavy-ion physics 1.6 0 π PHENIX (0–5%) CUJET 3.0 (h± + π0, 0–10%) a chance. He was motivated by arguments put forth by Reinhardt As far as the next decades are concerned, in view of the achieve- h± STAR (0–5%) Andrés et al. (0–5%) 1.4 Stock, Hans Specht, Rudolf Bock, William Willis and several ments realised in the past years and the remaining open questions, LHC 2.76 TeV (PbPb) v-USPhydro+BBMG (0–5%) other leading physicists, but the main arguments that convinced it is a safe bet that heavy-ion physics will continue to be a vigorous ALICE (0–5%) 1.2 ATLAS (0–5%) him came from Tsung Dao Lee during a VIP lunch at CERN. field of research on both sides of the Atlantic. What are the relevant CMS (0–5%) Schopper recalled: “I knew [Lee] from the parity-violation exper- degrees of freedom of the QGP: perturbative partons, pseudo-

AA 1.0 R iment. He had no direct personal interest and his physics motiva- particles, collective excitation of colour fields? Which dynamics tion sounded convincing. The main argument he put forward was drive the collision towards the formation of the QGP on timescales 0.8 SPS to find the theoretically predicted quark–gluon plasma, which On 9 November 2016, more than 400 physicists came to CERN to of a trillionth of a trillionth of a second, and in systems as small as a played an important role in the development of the universe.” celebrate three decades of heavy-ion physics. proton–proton collision? At which energy and which size does col- 0.6 RHIC When, in October 1986, oxygen-16 ions were successfully acceler- lectivity and statistical behaviour step in, and is chiral symmetry 0.4 ated by the SPS and fired into a fixed target of gold, the heavy-ion non-perturbative formulation of string theory, which along with restored in the QGP? programme began with a disparate ensemble of detectors recuper- the “AdS/CFT” correspondence provides tools to perform calcu- These are some of the unanswered questions in the heavy-ion 0.2 LHC ated from earlier high-energy experiments. Six different experi- lations for the QGP in the strongly coupled regime. field. Existing and planned facilities that offer varying collision ments were hatched, each with a different profile adapted to hunt Macroscopic properties of the QGP such as its density and systems combined with ever more sophisticated detectors and 0 the variety of observables predicted to accompany the QGP phase viscosity can now be determined with increasing precision by strong collaborations between the theory and experiment com- 1 10 100 p (GeV) transition: WA80 “Plastic Ball”; the NA34/2 HELIOS; the NA35 studying how the QGP, modelled by hydrodynamics, transports a munities are key to answering them. Based on what we are seeing T streamer chamber; NA36; WA85/94; and the NA38 muon-pair perturbation. Measurements include the value of high-order flow currently, heavy-ion veteran Reinhard Stock commented that we Measurements of the nuclear modification factors as a function of spectrometer. coefficients and nonlinear mode mixing, while the value ofη /S could be about to enter a new paradigm with impact across high- transverse momentum in central heavy-ion collisions at four In 1987, together with the increase of energy and the accel- (shear viscosity over entropy density) and its temperature depend- energy physics. That would perhaps reveal QCD to be some sort of different centre-of-mass energies, for neutral pions (SPS, RHIC), eration of sulphur beams, second-generation experiments con- ence have been pinned down within a factor two or less to 1/4π – low-energy limit to a more fundamental theory. charged hadrons (h±) (SPS, RHIC), and charged particles (LHC). taining innovative detector technologies were launched. Among which is the conjectured minimal value for a perfect quantum fluid. ● Values of RAA < 1 indicate that high-energy partons lose energy these were: NA49 with an ambitious time projection chamber; The microscopic structure of the QGP remains to be estab- Further reading while traversing the QGP and thus carry information about its CERES and its double ring imaging Cherenkov detectors; NA57 lished, with the help of hard probes to provide the required resolv- 30 Years of Heavy ions: ...what next? indico.cern.ch/event/457044/ colour-charge density. and its silicon tracking; and NA44, which contained a focusing ing power. Here, jet quenching has already become a mundane timetable. spectrometer that made use of cesium-iodide photocathodes for phenomenon with which to study the content and dynamics of data are pointing to unexpected similarities between observables the first time. The number of aficionados of this new and intrigu- the QGP. In turn, the same studies also hint at the ability of the Résumé measured in heavy-ion collisions and those measured in proton– ing field of investigation grew rapidly from a few hundred initial QGP to resolve the partonic shower. Quarkonia states, another Ions lourds : l’aventure dure depuis 30 ans lead or in high-multiplicity proton–proton collisions, perhaps hint- physicists to the several thousand from all over the world who hard probe, have also revealed rich dynamics. Their collision ing at yet another change of paradigm. work on today’s LHC, SPS and RHIC heavy-ion facilities. energy and transverse-momentum-dependent production can be Trente ans après la production des premières collisions The past 30 years have been an arduous path where every step understood in terms of two competing mechanisms: suppression ultra-relativistes au CERN, l’étude de la physique des ions lourds both reveals more knowledge to us while simultaneously generat- State of the art due to resonance melting by colour screening and regeneration est toujours d’actualité. Les collisions de haute énergie entre des ing new riddles. To mark the important achievements so far and Today, heavy-ion science is a thriving field of research, and it is due to coalescence of free heavy-flavour quarks, both provid- ions lourds et entre des protons constituent un système unique to discuss the long and thrilling future of heavy-ion physics, more notable that it is the common denominator in the physics pro- ing evidence for deconfinement. In addition, a flow signal has où étudier la dynamique de la matière dans l’univers primordial than 400 physicists met at CERN on 9 November last year to review grammes of all four major LHC experiments. On one hand, we been measured for open and hidden charmed mesons, raising the et tester les prédictions fondamentales de la chromodynamique what can be considered as one of the most vigorous fields at the have entered a phase of precision measurements of the QGP question of whether charm quarks participate in the collective quantique. Une série d’expériences faisant appel à des forefront of the high-energy physics programme. properties, while on the other hand the surprising similarities dynamics of the medium. collisionneurs et de prédictions théoriques remarquables ont between proton–proton and proton–nucleon collisions observed In general, the composition of the final hadronic state of the permis de jeter un nouvel éclairage sur le plasma quarks-gluons et A fitting celebration at the LHC lead us to question if the same dynamics are at work collision is quite well explained, assuming hadrons are formed in ont révélé qu’il a les propriétés d’un liquide parfait ; des mesures Although accelerators had been working with electrons and pro- in light and heavy systems. As demonstrated at the Quark Mat- a thermalised state with a temperature that closely matches the récentes laissent penser que ce domaine de recherche pourrait être tons for many decades, it was in 1974 when the Bevalac at Law- ter 2017 conference (see p39), many new results are generating temperature predicted for the QGP phase transition to the hadronic au seuil d’un nouveau changement de paradigme. rence Berkeley Laboratory accelerated the first ions to relativistic discussion. On the experimental side, these are based on a wealth phase. Surprisingly, fragile objects such as light nuclei appear to be energies (approximately 2 GeV per nucleon) and led to further of high-quality data collected produced and to survive at temperatures several times larger than Guy Paic, UNAM, Mexico, and Yves Schutz, IPHC, Strasbourg. programmes at BNL and CERN. The Bevalac beams were not both at LHC and RHIC for a energetic enough to create the necessary energy densities for the variety of collision systems QGP to form, and it required the ingenuity of accelerator physicists Quarkonia states, and energies, coupled with and the remarkable development of electron cyclotron resonance another hard probe, inventive analysis tools. On the (ECR) sources during the 1980s to take the decisive step toward have also revealed theory side, particular progress “ultrarelativistic” energies. has been made in relativistic The idea to launch an experimental heavy-ion programme at rich dynamics. hydrodynamics calculations. CERN came shortly after the SPS had enabled the discovery of Among many new and crea- the W and Z bosons in 1983. As the then CERN Director-General tive theoretical concepts is the

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The LHCb detector at CERN is one of several experiments where unusual hadrons have appeared in the past few years. Exotic hadrons bend Cerium Bromide (CeBr3) scintillation detectors the rules ● High resolution Your perfect partner C ● No 138La background for quality M ● 76 x 76 mm available vacuum components Y 4% @ 662 keV CM Half a century after the quark model was His primary focus was on the spectroscopy of baryons, which were MY interpreted as bound states of three quarks. Dalitz realised that the restrictions enforced by the Pauli exclusion principle led to a dis- CY devised, a number of hadrons have been tinct pattern of supermultiplets. Today, this simple model remains CMY discovered that appear to challenge its axioms. in excellent agreement with experiments, in particular for mesons K that comprise a quark–antiquark pair. Despite its success in matching empirical data, the theoretical Now available Fifty years have passed since Dick Dalitz presented his explicit underpinning of this non-relativistic model for light hadrons has on our new website constituent-quark model at the 1966 International Conference always been unclear. One of the remarkable features of hadron spec- on High Energy Physics in Berkeley, US. Murray Gell Mann and troscopy is that, half a century after the invention of the constituent- SCIONIX Holland B.V. T. +39.011.0968307 – F. +39.011.0968393 George Zweig independently introduced the quark concept in quark model, the particle data tables are filled with states that fit [email protected] - www.vaqtec.com Tel. +31 30 6570312 1964, and the idea had also been anticipated by André Petermann with a non-relativistic spectrum almost to the exclusion of anything Fax. +31 30 6567563 in a little-known paper received by Nuclear Physics in 1963. But it else. Quarks are but a few MeV in mass, and are therefore surely Email. [email protected] was Dalitz who developed the model and considered excitations of relativistic when confined within the 1 fm radius of a proton, yet the s www.scionix.nl quarks by analogy with the behaviour of nucleons in atomic nuclei. constituent-quark model treats them as if relativity plays no role.

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10 d d u u u d u d + d u d u mesons), four quarks and an antiquark (“pentaquark” baryons), in Z(4430) 10 e– ψ 3 101401 c 4.4 (4 S1) 3 + 6 addition to states comprised solely of gluons (“glueballs”). Fur- η 1 3 + 3 = c(4 S0) Y(4360) u 3 Front. Phys. Front. us χ d s d s u s thermore, combinations called “hybrids” in which the gluonic – 1 c2(3 P2) s s u hc(3 P1) χ 3 Y(4360) + c1(3 P1) fields entrapping the quark and antiquark are themselves excited Z2(4250) χ 3 γ 4.2 3 c0(3 P0) are also theoretically possible within QCD (figure 1). Glueballs, c X(4160) ψ(2 D ) s s u 1 tetraquarks and hybrid mesons, predicted in the late 1970s, can – Y(4140) e+ c + form correlations among a meson’s J, P and C quantum numbers Zc(4050) (b) J/ψ 1 3 + 2M d u d u d u 4.0 η (3 S ) ψ(3 31) Zc(4020) D* that are forbidden by the non-relativistic model. Indeed, it is the –c c 0 D ) 3 1 2 χ (2 P ) X(3940) + 3 c2 2 – – – lack of any empirical evidence for such exotic states in the meson Z (3900) Y(3915) χc1(2 P1) 3 3 3 c 3 + – χc0(2 P0) X(3872) MD+MD* spectrum that helped to establish the constituent-quark model in Fig. 2. At 4.6 GeV, e e annihilation produces DD1 at threshold. d s u s d s u s d s d u – – – – 3.8 the first place. It is therefore ironic that searches for such states at The (cu )(cu) content rearranges into (cc)(uu ) → J/ψππ. 3 ψʹʹ(1 D1)

mass (GeV/c 2MD modern experiments are now being used to establish the dynamic 3 (c) pentaquark H-dibaryon tetraquark η ʹ(21S ) ψʹ(2 S ) role of gluonic excitations in hadron spectroscopy. structures with a mass of around 4.4 GeV (CERN Courier Sep- c 0 1 3.6 u χ 3 d d u d u Although QCD is well tested to high precision in the per turbative tember 2015 p5). These have normal strong-interaction life- 1 c2(1 P2) hc(1 P1) –s d u u sd s – – χ 3 d s regime, where it is now an essential tool in the planning and inter- times and have been interpreted as clusters of three quarks plus c1(1 P1) pretation of experiments, its implications for the strong-interaction a charm–anticharm pair. Whether these are genuinely compact 3 3.4 χc0(1 P0) diquark–diquark– diquark–diquark– diquark–diantiquark limit are far less understood. Forty years after its discovery, and pentaquarks, or instead bound states of a charmed baryon and a antiquark diquark _ notwithstanding the advent of lattice QCD, hadron physics is still meson or some other dynamic artefact, they do appear to qualify established cc states (d) molecule hybrid glueball led by empirical data, from which clues to novel properties in the as “exotic” in that they do not fit easily into a traditional three- 3.2 predicted, undiscovered g – strong interactions may emerge. The search for exotic hadrons is constituent picture. d 3 neutral XYZ mesons π,... d – J/ψ(1 S1) s u an essential part of this strategy, and in recent years several new There have also been interesting meson sightings at lepton d charged XYZ mesons –u g hadrons have been discovered that do not fit well within the tradi- colliders in recent decades. Electron–positron annihilation above 1 3.0 ηc(1 S0) tional quark model. energies of 4 GeV in numerous experiments reveals a series of 0–+ 1– 1+– 0++ 1++ 2++ Fig. 1. Some of the ways in which QCD allows quarks to arrange peaks in the total cross-section that are consistent with radial JPC into hadrons: (a) a red and blue quark triplet produces a Strange sightings excitations of the fundamental cc– J/ψ meson: the ψ(2S), ψ(4040), magenta (anti-green) antitriplet and sextet; (b) three With hindsight, one of the first clues to the existence of quarks ψ(4160) and ψ(4415), which are non-exotic and fit within the Fig. 3. The spectrum of charmonium and charmonium-like anticoloured diquark antitriplets; (c) exotic, colour-singlet came in the 1950s from measurements of cosmic-ray interactions non-relativistic spectrum. Evidence for exotic mesons has come candidates. states formed from quarks, antiquarks, diquarks and in the atmosphere, which revealed hadrons with unusual pro- from data on specific final states, notably those containing a J/ψ diantiquarks; and (d) other possible multiquark/gluon systems. duction and decay properties. These “strange” hadrons, we now with one or more pions, which have revealed several novel states. channel containing a pion and a charmonium meson. Since it can – know, contain one or more strange quarks or strange antiquarks, Historically, the first clue for an exotic charmonium meson of carry electric charge, this state must contain ud (or du–) in addition In the case of mesons, which fit the quark model arguably even yet history has left us with a perverse convention whereby this type above a mass of 4 GeV came around a decade ago from to its cc– content, and therefore cannot be explained as a bound state better than baryons, this incongruity is especially significant. When strange quarks are deemed to carry negative strangeness, and the BaBar experiment at SLAC in the US. Analysing the pro- of a single quark and antiquark. In principle, these states should be Dalitz spoke in 1966, it made sense to emphasise baryons because strange antiquarks are positive. Thus mesons can have one unit of cess e+e– → J/ψππ, researchers there found a clear resonant-like accessible in decays of B mesons, but there is no sign of them so far. they outnumbered the known mesons at that time. Following the strangeness, in either positive or negative amounts, while baryons structure dubbed Y(4260), which has no place in the qq– spectrum Nonetheless, B decays are a source of further exotic structures. discovery of charm and heavy flavours in the late 1970s, however, can have strangeness –1, –2 or –3 (antibaryons, in turn, can have because its mass lies between the ψ(4160) and ψ(4415) cc– states. For example, the invariant-mass spectrum of B → K π±ψ(2S) con- the spectroscopy of mesons flourished and the correlations among positive strangeness). More remarkably, this state decays into charmonium and pions tains a structure called the Z(4430) observed by Belle and LHCb in a meson’s spin (J), parity (P) and charge conjugation (C) were also A bar yon with positive strangeness (or an antibar yon with nega- with a standard strong-interaction width of the order of 100 MeV the ψ(2S)π invariant-mass spectrum, which contains both hidden found to be in accord with those of a non-relativistic system. tive strangeness) is therefore classed as exotic. The minimal con- rather than 100 keV, which is more typical for such a channel. charm and isospin and hence must contain (at least) two quarks Following Dalitz’s description of the baryon spectrum, Green- figuration for such a baryon would involve four quarks together The clue to the nature of this meson appears to be that the mass of and two antiquarks. These features first need to be established as berg, Nambu, Lipkin and others noted that the model’s ad-hoc cor- with the strange antiquark, giving a total of five and the techni- the Y meson (4260 MeV) is near the threshold for the production of genuine and not artefacts associated with some specific produc-

relation of baryon spins with the constraints of the Pauli principle cally incorrect name of “pentaquark”. A claim to have found such DD1 – the combination of pseudoscalar (D) and axial (D1) charmed tion process. Their appearance and decay in other channels would required some novel degree of freedom, which we call “colour”. a state – the θ(1540) – made mesons (figure 2). This is the first channel in e +e– annihilation where help in this regard, while the observation of analogous signals for The advent of quantum chromodynamics (QCD) in the 1970s pro- headlines nearly two decades charmed meson pairs can be produced with no orbital angular other combinations of flavour may also signpost the underlying – vided the rationale for this concept, explaining the existence of The empirical guide ago but is now widely disre- momentum (i.e. via S-wave processes). Thus at threshold there is no dynamics. If real, these states are the product of charmonium cc quark–antiquark or three-quark combinations in terms of colour- garded. The scepticism was not angular-momentum barrier against a DD1 pair being created effec- and light-quark basis states (a summary of charmonium candidates singlet clusters. But QCD did not explain the non-relativistic pat- of the quark model is that a pentaquark exists, since tively at rest, and rearranging their constituents into the form of J/ψ can be seen in figure 3). tern of states. Feynman, who in his final years devoted his attention so well established QCD can accommodate such and light flavours (the latter then seeding pions). Thus the structure to this issue, asserted: “The [non-relativistic] quark model is cor- that hadrons outside a state, but that it appeared to could simply be a threshold effect rather than a true resonance, or an Proceed with caution rect as it explains so much data. It is for theorists to explain why.” be anomalously stable. More exotic “molecule” made of D and D1 charmed mesons. It is clear that peaks are being found that cannot be interpreted as Today, physicists still await this explanation. Yet the empirical of this straitjacket recently, the LHCb experiment The decay of the Y(4260) into J/ψππ reveals a manifestly exotic qqq or qq– clusters. But one should not leap to the conclusion that guide of the quark model is so well established that hadrons outside are deemed “exotic”. at CERN’s Large Hadron Col- structure. The J/ψπ± channel is electrically charged with a pro- we have discovered some fundamentally novel state built from, say, of this straitjacket are deemed “exotic”. lider (LHC) reported decays nounced peak called Z(3900), as reported by both the BESIII diquarks and antidiquarks or, for baryons, a pentaquark. A qq –qq–

Although the restriction to colour singlets within QCD explains of the Λb pentaquark-like experiment in China and Belle in Japan in 2013. Another sharp peak “tetraquark”, for example, looks less exotic when trivially rewritten s the existence of qq– and qqq hadrons, it raised the question of why baryon that revealed similar observed by BESIII – the Z(4020) – appears in the flavour-exotic as qq– qq–, which is suggestive of two bound conventional mesons.

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● Further reading D* D Fig. 4. “Deusons” arise from anticipate meson molecules (or, by analogy with the deuteron, appearance of a state near the corresponding S-wave threshold. _ _ pion exchange. Pion exchange “deusons”), which would take us beyond the simple quark-model In some of these cases, but not all, the familiar forces of conven- F Close 2017 The New Cosmic Onion: Quarks and the Nature of the Universe c u u c is the source of an attractive spectroscopy. The Y(4260) could be an example of such a state, tional nuclear physics play a role, and the multi-particle events at (Taylor and Francis). – – S L Olsen 2015 Front. Phys. 101401. force between D and D* or D since both DD1 and D*D0 S-wave thresholds lie in this region and the LHC have the kinematic reach to include all combinations of 10 and D* charmed mesons. This pion exchange may play a role in linking the two channels (figure non-strange, strange, charm and bottom mesons. How many of A Petermann 1965 Nucl. Phys. 63 349. also occurs between D and D* 4). If these states are indeed deusons then there should also be these can in practice be identified is the challenge, but identifying analogous to the case of the partners with isospin. Establishing whether these structures are the dynamics of states “beyond qq– ” may depend on it. Résumé deuteron. singletons or have siblings is therefore another important step in In conclusion, these exotic states need to be studied in differ- Les hadrons exotiques font plier les règles identifying their dynamical origins. ent production mechanisms and in a variety of decay channels. A

_ _ The first sign of deusons may be expected in the axial-vector genuine resonant state should appear in different modes, whereas 50 ans après la création du modèle des quarks, certains hadrons c u u c channel formed from a pseudoscalar and vector charmed (or bot- a structure that appears in a single production mechanism and a semblent défier ses axiomes. Si la correspondance avec les données _ D D* tom) meson. This is because pion exchange can occur between unique decay channel is suggestive of some dynamical feature that empiriques est une réussite, la fondation théorique de ce modèle non _ a pair of vector mesons or as an exchange force between a is not truly resonant. While interesting in its own right, such a state relativiste pour les hadrons légers n’a toutefois jamais été claire. Les * D D pseudoscalar-vector combination, but not within a state of two is not “exotic” in the sense of hadron spectroscopy. résultats d’expériences telles que BESIII, Belle et LHCb indiquent des pseudoscalars as this would violate parity conservation. The As for truly exotic states, there are different levels of exotic- pics qui ne peuvent pas être interprétés comme des états traditionnels enigmatic state X(3872), which was first observed in B decays ity. For flavoured hadrons: the least exotic are meson analogues à deux ou à trois quarks. Il ne faudrait toutefois pas en conclure – 0 π by Belle in 2003 and occurs at the D0 D* + cc threshold, has of nuclei – “deusons” driven by pion exchange between pairs of hâtivement la découvert d’un état fondamentalement nouveau formé long been a prime candidate for a deuson. If so, there should mesons. Next are “hybrids”: states anticipated in QCD where the de diquarks et d’antidiquarks ou, pour les baryons, un pentaquark. – be analogous states in the BB* as well as charm-bottom flavour gluonic degrees of freedom are excited in the presence of quarks Ces états exotiques doivent d’abord être étudiés dans différents mixtures and perhaps siblings with two units of charm or bot- and/or antiquarks. Finally, the most exotic of all would be colour- mécanismes de production et divers canaux de désintégration. _ D’ici-là, ils garderont le même statut que la vie extraterrestre : même DD* tom. Whether these states have charged partners is one of many singlet combinations of compact diquarks, which are allowed in model-dependent details. That some of these states should occur principle by QCD and would lead to a rich spectroscopy. At pre- si nous imaginons que ces êtres doivent exister dans la richesse de la Indeed, these could be the two mesons in the invariant mass of seems unavoidable, however, and if doubly charmed states exist sent their status is like the search for extraterrestrial life: while nature, ils semblent vouloir rester cachés. which the peak was seen. Unless the peak is seen in different chan- they should be produced at the LHC. one feels that in the richness of nature such entities must exist, nels, and ideally in different production mechanisms, one should Whereas for baryons the attractive forces arise in the exchange they seem reluctant to reveal themselves. Frank Close, University of Oxford, UK. be cautious. or “t channel”, for pairs of mesons there can also be contributions For example, when three or more hadrons are produced in a sin- due to qq– annihilation in the direct s-channel. In QCD this can also gle decay it is common to discover peaks in invariant-mass spec- mask the search for glueballs: for example, the scalar glueball of tra just above the two-body thresholds. These are not resonances, lattice QCD predicted at a mass of around 1.5 GeV mixes with the although papers on the arXiv preprint server are full of models nonet of scalar qq– states in this very region. The pattern of these built on the assumption that they are. Instead, the peaks likely scalars empirically is consistent with such dynamics. arise due to competition between two effects. First, phase space Scalar mesons are interesting not least because the theoretical opens up for the production of the two-body channel, but as the interest in multiquark or molecular states originated in such par- invariant mass increases, the chance of this exclusive two-body ticles 40 years ago, after Robert Jaffe noticed that the chromo- mode dies off because the probability for the wavefunctions of magnetic QCD forces are powerfully attractive in the nonet of the two hadrons to overlap decreases. Any peak seen within a few light-flavoured scalar mesons. Intriguingly, this idea has remained Journal of Physics series hundred MeV of such a threshold is most likely to be the acciden- consistent with the observed nonet of scalars below 1 GeV ever tal result of this phenomenon. Such “cusps” have been proposed since. The main question that remains unresolved is to what extent Celebrating 50 years of leading physics as explanations of several recent exotic candidates, such as the these states are dominantly formed from coloured diquarks and • Join more than 40 Nobel Prize laureates and publish your Z(3900) and Z(10610) spotted at BESIII and Belle, among others. their antidiquarks, or are better described as molecular states latest research in the Journal of Physics series. Whether the tetraquark candidates X(4274), X(4500) and X(4700) formed from colour-singlet π and K mesons. • Articles in the series were downloaded more than 3.4 million recently observed at LHCb, in addition to the X(4140) found by LHCb in particular has shown that it is possible to identify light times in 2015. the CDF experiment at Fermilab in 2009, herald the birth of a new scalars among the decay debris of heavy-flavoured mesons, offer- • Journal of Physics articles were cited more than 114,000 QCD spectroscopy or are examples of more mundane dynamics ing a new opportunity to investigate their nature and dynamics. times in 2015. such as cusps, is also the subject of considerable debate. In short, Indeed, the kinematic reach of the LHC potentially enables a mul- if a peak occurs above a two-body threshold in a single channel: titude of information to be obtained about heavy-flavoured mesons Find out more about the prestigious Journal of Physics series beware. in both conventional and exotic combinations. We might therefore at iopscience.org. hope that information about exotic mesons will be extended into Enter the deuson different flavour sectors to help identify the source of the binding. More interesting for exotic-hadron studies are peaks that lie just below threshold. Such states are well known in the baryon sector, Remarkably robust the deuteron being a good example. The nuclear force driven by In general, the simple qq– picture of mesons appears to remain pion exchange that binds neutrons and protons inside the atomic remarkably robust so long as there are no nearby prominent chan- nucleus should also occur between pairs of mesons, at least for nels for pair production of hadrons in the S-wave channel. “Exotic” those that are stable on the timescale of the strong interaction. Thus mesons and baryons seem to correlate with some S-wave channel on purely phenomenological and conservative grounds, we should sharing quantum numbers with a nominal qq– state and causing the

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CCApr17_HADSPEC.indd 34 08/03/2017 15:40 CCApr17_HADSPEC.indd 35 Journal of Physics08/03/2017 16:36 series CERNCOURIER www. Celebrating 50 years of leading physics V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 Be in great company Join more than 40 Nobel Prize laureates and publish your latest research in the Journal of Physics series.

Extend the impact of your research Articles in the series were downloaded more than 3.4 million times in 2015.

Raise your visibility amongst your peers Journal of Physics articles were cited more than 114,000 times in 2015.

Find out more about the prestigious Journal of Physics series at iopscience.org. CERN Courier April 2017

Company Proole Founded in Mantua, Italy in 1947, Belleli Energy Faces & Places CPE deenes solutions for the Gas Monetization, Oil & Gas Downstream and Nuclear markets. The in-house design, engineering and Italian Mechanical Engineering manufacturing allow the company to ensure Piping and Components, Eurodif uranium enrichment meets global challenges integrity of materials, processes and products A ppointments from raw materials through fabrication, to completed products. Its headquarters in Mantua (Italy), are the largest New director for Jefferson Lab facilities in Europe for producing heavy wall reactors, shell and tube heat exchangers. The plant has direct access to an international harbor, Accelerator physicist Stuart Henderson, Stuart Henderson has extensive experience allowing to manufacture some of the world’s largest equipment and to transport it from its 53, has been named the fourth director of with US national laboratories. own docks to facilities around the world. the Thomas Jefferson National Accelerator With a total area of over 280.000 sqm and 60.000 Facility in Virginia, US. Currently director includes the $338 million 12 GeV Upgrade sqm of covered buildings (including offices of the Advanced Photon Source upgrade Project and construction of a $70 million Vessel for the Sodium Pumps containment headquarters and workshops), Belleli Energy CPE project at Argonne National Laboratory, he addition to the lab’s engineering and design owns one of the best equipped and referenced will start his new role on 3 April. Prior to Laboratory National Argonne facilities. “I’m thrilled to be taking the helm manufacturing facility to satisfy its clients requests. The combination of large spaces, joining Argonne, Henderson was associate of Jefferson Lab, particularly at this time big-size manufacturing and very favorable global laboratory director for accelerators at of tremendous opportunity and potential,” shipping conditions enables Belleli to satisfy all Fermilab and before that he spent almost a says Henderson. “Jefferson Lab plays a very kind of requests for sophisticated process decade at Oak Ridge National Laboratory’s who came to Jefferson Lab as director in special role in furthering the Department of equipment of any size and weight. Belleli Energy Spallation Neutron Source (SNS), where 2008 from Fermilab and will continue his Energy mission, both through its operation CPE’s Quality Management System complies with he led the transition to successful user association with the facility as director of a world-class nuclear-physics research the ISO – 9001 Standard, ASME Code Section VIII Div.1 & VIII Div.2 and also satisees the European operations at megawatt-beam power levels. emeritus. Jefferson Lab has enjoyed facility, and through its world-renowned Pressure Equipment Directive 97/23/EC, Chinese Henderson replaces Hugh Montgomery, significant growth in recent years, which technology capabilities.” and Russian Regulations. The company is periodically and successfully assessed by ASME, Voss, the latest voice of the EPS. Det Norske Veritas, TUV, Chinese and Russian Rüdiger Voss next CERN Delegations. Tube Bundle of the Sodium Air Heat Exchanger Voss wants to strengthen global co-operation and networks and raise the voice of science Belleli Energy CPE - Via Taliercio 1, 46100 Mantova, Italy - Phone : +39-0376-490.1 - Web site: www.belleli.it president of EPS in the face of Europe’s changing political landscape, which he says poses severe threats Former CERN staff member Rüdiger Voss to cross-border collaboration, the mobility of has been appointed president of the European students and researchers, and equal access to Physical Society (EPS), beginning 1 April European funding and infrastructures. “The and effective for two years. Established in inelastic muon–nucleon scattering at EPS, representing a scientific discipline with 1968, the EPS represents 42 national physical CERNʼs SPS in 1982, joined CERN as a a highly developed culture of international societies, which in turn represent more than research physicist in 1987. Following various collaboration, has a special responsibility to 120,000 members. It has a similar number of group-leader positions in the experimental- voice a strong opinion in this discussion,” he associate members – mostly major research physics division, in 2009 he became a senior says. “This concern is not unique to physics, institutions such at CERN – and about 3500 adviser for international relations and then and needs to be addressed by the scientific individual members. head of the unit from 2013 to 2015. community at large.” (See “European Hermetic Sealing Voss, who completed a PhD in deep Among his many goals as EPS president, organisations uphold scientific values” on p9.) ® ARMCO Pure Iron A w A r d s High Purity Iron for Neutrino trio wins 2016 Pontecorvo Prize

Magnetic Applications The Joint Institute for Nuclear Research THE (JINR) in Dubna, Russia, has selected the winners of the Bruno Pontecorvo Prize, which is awarded each year for significant HERMETIC advances in elementary particle physics. The 2016 recipients, who are recognised for their SEALING outstanding contributions to the study of neutrino oscillations and to the measurement (Left to right) Yifang Wang, Soo-Bong Kim and Koichiro Nishikawa. of the θ13 mixing angle using the Daya Bay, RANGE RENO and T2K experiments, are: Yifang spokesperson for the Reactor Experiment for his memory two years afterwards. It was Wang of the Institute of High Energy Physics Neutrino Oscillation (RENO) in South Korea Pontecorvo who in 1957 suggested that in Beijing, China; Soo-Bong Kim of Seoul and Nishikawa is the founding spokesperson neutrinos might change from one type to Exclusive manufacturing National University, South Korea; and of the T2K and K2K experiments in Japan. another. The experimental discovery of of vacuum feedthroughs Koichiro Nishikawa of the KEK Laboratory The 2016 prizewinners will receive the award neutrino oscillation half a century later in Tsukuba, Japan. at a ceremony in September. by Super-Kamiokande and the Sudbury Visit us at Wang pioneered the Daya Bay neutrino Bruno Pontecorvo died in 1993 at Neutrino Observatory was recognised with www.aksteel.eu oscillation experiment in China, while Kim is Dubna, and the prize was instituted in the 2015 Nobel Prize for Physics. www.hermetic-sealing.com IPACBooth 2017 #9 37

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CCApr17_Faces&Places.indd 37 08/03/2017 16:40 CERNCOURIER www. V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 CERN Courier April 2017 CERN Courier April 2017 Faces & Places Faces & Places

AAAS honours C o n f e r e n C e s Kurt Gottfried Highlights from Quark

Kurt Gottfried, professor emeritus of physics Matter 2017 at Cornell University and a renowned authority on nuclear-arms control, has been C Behnke/GSI Image credits: (left to right) CERN; ESRF, Fermilab awarded the 2016 Scientific Freedom and Responsibility Award from the American Association for the Advancement of Science (AAAS). Gottfried, an expert in quantum EPS announces theory who was a visiting scientist at CERN PT2026 NMR Precision Teslameter in the 1960s, was honoured “for his long and accelerator distinguished career as a ‘civic scientist’, through his advocacy for arms control, Reach new heights human rights and integrity in the use of prizes science in public policymaking”.

in magnetic eld Gottfried The European Physical Society (EPS) helped to measurement accelerator group has announced the found the winners of the 2017 accelerator prizes, to be Union of Cornell UniversityCornell presented on 18 May during the International Concerned The Metrolab PT2026 sets a new Particle Accelerator Conference (IPAC17) in Scientists. standard for precision magnetometers. Copenhagen. Leveraging 30 years of expertise building Lyn Evans of CERN receives the Rolf Quark Matter 2017 participants at the Hyatt Regency Chicago in February. Wideröe Prize for outstanding work in the the world’s gold standard magnetometers, accelerator field. He is rewarded for his The 26th Quark Matter conference, in lead–lead collisions. Both ALICE and it takes magnetic  eld measurement to many major accomplishments in the field devoted to ultra-relativistic nucleus– CMS also presented novel analyses of new heights: measuring higher elds with of accelerator design, construction and Julius Wess Award nucleus collisions, was held in Chicago on the correlations between different flow operation, in particular his contributions to 5–11 February. Following a pre-conference coefficients, while CMS quantified the better resolution. the SPS and his leadership of the design and for detector work student day that attracted nearly 400 young differences between D-meson flow and construction of the LHC. Research at the SPS scientists, the main event had more than light-hadron flow for v2 and v3, which inform The PT2026 offers unprecedented  exibility led to the discovery of the W and Z bosons, Robert Klanner of the University of 700 registered participants. Overviews of us about differences in the interactions of while the LHC uncovered the Higgs boson Hamburg and DESY has been nominated for the most recent results from experiments, light partons and heavy quarks with the hot in the choice of parameters, interfacing in 2012. the 2016 Julius Wess Award for outstanding spanning the entire energy range from medium. ATLAS showed new results on and probe placement, as well as greatly The Gersch Budker Prize for a recent achievements in elementary particle and the SIS 100 accelerator at GSI Darmstadt heavy-flavour flow in proton–lead collisions. improved tolerance of inhomogeneous significant, original contribution to the astroparticle physics. The award, established to the highest energies at CERN’s LHC, These results were complemented by accelerator field goes to Pantaleo Raimondi in 2008 by the KIT Elementary Particle and were followed by almost 200 parallel more detailed analyses from RHIC in the elds. And with Ethernet & USB interfaces of the ESRF in Grenoble in recognition of his Astroparticle Physics Center, recognises presentations, 30 plenary talks and a session US, revealing the mass ordering of flow and LabVIEW software, it  ts perfectly into invention of a new storage-ring lattice called Klanner’s fundamental contributions to the with more than 300 posters. coefficients and heavy-flavour flow measured modern laboratory environments. the “hybrid multi-bend achromat”. The novel development of silicon-microstrip detectors, Nucleus–nucleus collisions have long by the STAR experiment, and small-system design will reduce the emittance of the ESRF in particular for achieving the resolution been known to display characteristic collectivity including proton–gold, deuteron–

www.agence-arca.com - Photo: Scott Maxwell, Master le - Photo: Scott Maxwell, Master www.agence-arca.com light source by a factor of 30 and has also required to reconstruct secondary vertices signatures of collectivity, and this was one gold and helium–gold collisions measured been adopted as the basis for the design of from the decay of heavy-flavoured hadrons. of the main themes at the Chicago event. by PHENIX. several other next-generation light sources. In the early 1980s, together with Gerhard Collectivity is typically quantified in terms Theory-overview talks focused on Finally, the Frank Sacherer Prize Lutz and the late Josef Kemmer, Klanner of flow coefficients, vn, where n corresponds the validity of relativistic fluid dynamic recognising an individual in the early part of used planar processes to build a silicon-strip to a particular harmonic in the azimuthal simulations supplemented with realistic initial his or her career goes to Anna Grassellino of detector, and in doing so initiated the culture distributions of produced particles. Since the conditions and properties of the hot-partonic Fermilab, for her major impact on the field of flavour-tagging in particle physics. first LHC proton–lead run in 2013, it has been and the hadronic phases. The extent to which of superconducting RF technology. The known that sizeable vn are also observed in the simulations can account for collectivity in techniques of nitrogen doping and “nitrogen proton–lead collisions and even in detailed soft-particle production, and in particular how infusion” developed by Grassellino have Klanner’s analyses of high-multiplicity proton–proton global Bayesian analyses that are novel for this already been applied to accelerator projects DESY work led to collisions. field can be used to zoom in on fundamental and have the potential to significantly reduce the rapid At this year’s conference, the LHC’s properties of the quark–gluon plasma, was

Pantone 286 Pantone 032 the cryogenic load and improve the energy development ALICE experiment presented novel results the subject of many parallel talks. In addition efficiency of superconducting linacs. of micro- on identified particle flow. The data show to details of these analyses, the Chicago structured that φ mesons flow like pions and kaons, that conference discussed the new challenges (Top, left to right) EPS prizewinners Lyn silicon heavy-flavoured D mesons display sizable for theory and experimental analyses that Magnetic precision has a name www.metrolab.com

Evans, Pantaleo Raimondi and Anna detectors. collectivity above 10 GeV and that even arise from characterising and understanding s Grassellino. J/ψ mesons partake in collective motion collectivity in smaller systems.

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Another highlight of the event was progress number of well-known measurements collisions, which may yield novel constraints was the determination of the very first containing all publicly available TMDs and impact on the precision of LHC predictions. on the topic of hard probes. Since the first have been repeated using the much larger on the nuclear dependence of parton complete transverse-momentum-dependent visualisation tools. Although still a small community, the range experiments at RHIC, it has been known data samples of LHC Run 2 to improve the distribution functions, to new precision parton distributions, which are valid over The REF workshop series, which started in of applications of TMD approaches cover the that the yield of high-pT final-state hadrons measured kinematic ranges and statistical measurements of the sequential suppression the full range of momentum accessible at 2014, is unique because it addresses questions most interesting and important regions where is suppressed or “quenched” by a factor of accuracy. In particular, ATLAS showed of bottomonium states at CMS. New the LHC. Progress has been reported in the from high-energy particle collisions together resummation to all orders in perturbation around five in central heavy-ion collisions. nuclear modification factors for jets that results from RHIC also included a first region of very small longitudinal momenta, with issues coming from the non-perturbative theory is relevant, and which is the major Measurements at the LHC have extended reveal a factor of two suppression for jets with measurement of the charmed Λc baryon by where saturation effects typically appear. structure of hadrons. These are very new and focus of new and challenging Standard Model the dynamic range of these measurements a transverse energy up to 1 TeV, while both the STAR experiment, which provides a new New tools for transverse-momentum- exciting attempts to describe in a uniform measurements at the LHC. The next edition and have gradually made a whole new set ATLAS and CMS presented much improved way to test hadronisation models. We also dependent parton distributions (TMDs) manner the low- and high-energy behaviour of the REF workshop will be held in Madrid, of jet-based probes available. The last two measurements of the energy imbalance for saw the first measurements of net particle were reported, including a complete library of particle collisions, which has much Spain, from 13 to 17 November 2017. years have also seen a strong push towards photon jets and CMS presented Z-boson-jet moments by ALICE, which provide a critical analysing jet substructures with modern pairs, which provide precise information reference for fluctuation measurements in the analysis techniques, and Quark Matter 2017 about the probability distribution for energy RHIC beam-energy scan. Celebrating a decade of high-end computer algebra featured the first detailed public discussion of loss. An exciting future perspective is that Space was also given to discussions of

such developments. For instance, researchers a detailed analysis of the softening of jet the physics plans for the LHC heavy-ion C Koutschan are exploring novel opportunities for fragmentation may provide experimental programme in Run 3 and beyond, as well Precision calculations of scattering characterising jet-medium interactions and access to the microscopic mechanisms as the planning for the new “sPHENIX” processes at high-energy colliders such medium-induced parton splittings based on underlying equilibration processes in the hot detector at RHIC that has recently passed as the LHC rely on advances in computer so-called “groomed” jet variables, such as and dense medium. an important review and is expected to take algebra to process the enormous number the groomed zg distributions measured by There were many further highlights first beam in 2022. Participants now have of higher-loop Feynman integrals. For the CMS and STAR or jet-mass measurements at Quark Matter 2017. Results ranged 15 months to consider the presented results past 10 years, the DESY theory group at presented by ALICE. from the ATLAS measurement of dijet and make progress before the next Quark Zeuthen has collaborated in this field with Apart from these new observables, a photoproduction in ultra-peripheral Matter meeting in Venice in May 2018. mathematicians from the Research Institute of Symbolic Computation (RISC) at (From left to right) Joachim Mnich (DESY), Peter Paule (RISC), Johannes Blümlein Johannes Kepler University (JKU) in Linz. (DESY), Carsten Schneider (RISC) and Alexander Egyed (JKU). Slush brings scientists and entrepreneurs closer During the collaboration, various symbolic summation and integration packages, as Castle in Austria on 7 February, during precision calculations for the LHC and new well as those for related special functions, which representatives of DESY and JKU developments in q-series. With an astonishing 17,500 attendees, one Marthe Dehli of CERN’s Knowledge have been created. These are publically extended their collaboration agreement C o r r e C t i o n

million livestream viewers and thousands KauttuP Transfer Group was a keynote speaker at available and offer broad automation of for a further five years. The directors of participating start-up companies and Slush Science Track in December. analytic Feynman integral calculations for of research at Wolfram Research and venture capitalists, Slush is Europe’s leading two- and three-loop integrals. MapleSoft also contributed reports on the A photograph on p41 of the March issue shows entrepreneurship event. Among accredited is through starting new ventures, and To mark the 10th anniversary of latest versions of Mathematica and Maple, Claude Trudelle, Québec delegate general for business founders and investors, CERN was CERN is committed to building a culture of this successful partnership, a one-day while special lectures were delivered Germany, Austria and Switzerland, and not invited to give a keynote speech at the 2016 entrepreneurship among its scientists and workshop took place at Hagenberg about summation theory, elliptic solutions, Rémi Quirion as stated in the caption. edition of the annual event, held in Helsinki, engineers to help maximise the impact of Finland, at the start of December. With CERN on society. Vice versa, new initiatives V i s i t s

Slush aiming to aid the next generation of such as Slush Science Track have brought CERN S Bennett, world-conquering companies and CERN academic research into the spotlight by Director-general of Marie-Christine Marghem, Belgian minister aiming to find answers to fundamental gathering top-quality research and offering the United Nations for energy, environment and sustainable questions about the universe, you might a €100,000 prize for the best basic research Office,Michael development, came to CERN on 20 February. wonder what these two organisations have both communities have started to realise presented. Slush underpins its initiative by Bennett/CERNS Møller, visited CERN Following a tour of CMS, she signed the in common. that the benefits of co-operating are remarking that “all inventions come from on 6 February with guestbook with (left to right): CERN director for Although there has traditionally existed a reciprocal. One of the ways innovations and science, and that today’s findings will lead to other heads of United accelerators and technology Frédérick Bordry, gap between science and entrepreneurship, know-how can be applied more generally products years later”. Nations agencies, Belgian ambassador to the UN Geert Muylle, during which they CERN Director-General Fabiola Gianotti, and P Van Mechelen toured the ATLAS CERN director for research and computing Antwerp workshop cavern and visited the Eckhard Elsen. sets reference LHC tunnel. M Brice/CERN - At the beginning of November, at the Ofir Akunis, minister Edgars Rinkevicˇs, minister of Resummation, Evolution, Factorization of science, technology foreign affairs for the Republic (REF) meeting, about 40, mostly young, and space in Israel, of Latvia, came to CERN on

scientists met in Antwerp in Belgium to Bennett/CERNS visited CERN on 27 February and visited the discuss limitations in present calculations and 22 February, during CMS experiment. He signed the simulations concerned with Standard Model which he toured ATLAS guestbook with CERN director processes. These limitations, which concern Participants at the 2016 REF workshop. with former experiment for international relations the physics programme both at the LHC spokesperson Peter Charlotte Warakaulle and and at future lepton–hadron colliders, come transverse momenta shed light on the intrinsic collinear evolution and parton-distribution Jenni (left). non-Member State adviser from neglecting the transverse momenta that hadronic structure, while large transverse functions, these transverse momenta are not Christoph Schaefer. arise in the QCD evolution of initial-state momenta can change the kinematics considered explicitly. partons during collisions. Very small of processes significantly. In the usual One of the highlights of the workshop

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CCApr17_Faces&Places.indd 40 08/03/2017 15:56 CCApr17_Faces&Places.indd 41 08/03/2017 15:56 CERNCOURIER www. V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 CERN Courier April 2017 CERN Courier April 2017 Faces & Places Faces & Places Silicon Drift Detectors • Solid State Design • Easy to Use O b i t u a r i e s much appreciated. Hans Jürgen was always honesty, directness of speech and dedication • Low Cost ready to hear different opinions and did to CERN and its experiments. not hesitate to take difficult decisions. His In his private life, Hans Jürgen’s wide Ned Goldwasser 1919–2016 extensive knowledge and experience with interests, his love of classical music and FAST SDD® various detector technologies paired with his great care in all personal relations were a co-ordination skills earned him credibility continuous inspiration to his family and Count Rate = >1,000,000 CPS Edwin Goldwasser, deputy director of join the central design group of the proposed and authority. Colleagues who had the friends. Our deepest sympathy goes to his Fermilab when the laboratory was founded Superconducting Super Collider facility, pleasure to work closely with Hans Jürgen wife, children, brother and their families. Resolution Peaking Time Fermilab in 1967, died on 14 December at the age of where he served as associate director until will never forget him and his intellectual ● His friends and colleagues. 125 eV FWHM 4 µs 97. Goldwasser oversaw the construction 1988. In 1990, following his retirement 130 eV FWHM 1 µs of Fermilab (or the National Accelerator from the university, he was appointed a 140 eV FWHM 0.2 µs Laboratory, as it was then known), completing distinguished scholar at the California 160 eV FWHM 0.05 µs it on time and under budget. He also scheduled Institute of Technology (Caltech) to work on Jean Yoccoz 1925–2016 its experimental programme, managed the LIGO project. its programme Advisory Committee Goldwasser did his undergraduate work SDD Spectrum 5.9 and implemented its groundbreaking at Harvard University. Following service as Jean Yoccoz, one of the pioneering directors keV 55 equal-employment programme. Goldwasser a physicist with the US Navy, he received of the French National Institute for Nuclear Fe remained as the laboratory’s deputy director his PhD in physics from the University of Physics and Particle Physics (IN2P3), passed eV FWHM

Counts 125 until 1978, taking an extended leave of California, Berkeley, then served a year away on 30 December at the age of 91. 25 mm2 x 500 µm N G and S Yoccoz absence from the University of Illinois to on the faculty there before moving to the Born into a modest peasant family in 11.2 µs peaking time 6.4 keV serve at the new facility. Ned Goldwasser in 1967 at the National University of Illinois in 1951. Savoie, Yoccoz succeeded brilliantly in his P/B Ratio: 20000/1 “When Ned took leave from the University Accelerator Laboratory. “Ned was a natural leader, who was studies and was admitted to Ecole Normale Energy (keV) of Illinois to help create Fermilab from green instrumental in making Fermilab a place Supérieure in Paris. Attracted by theoretical Resolution vs Peaking Time fields, the project took on new dimensions: contagious yet critical enthusiasm for the where both physics and physicists thrived,” nuclear physics, he entered Frédéric Joliot’s 180 25 mm2 a truly effective concern for the variety of discoveries made possible.” says Barry Barish, professor emeritus of laboratory in Collège de France and then 170 people to build it, and a dedication to make it After setting Fermilab firmly on its feet, physics at Caltech and the first director of joined Rudolf Peierls at the University of both fruitful for its users and attractive for the Goldwasser returned to the University LIGO. “I will personally miss his wisdom and Birmingham in the UK, where he undertook 160 Standard SDD professional development of its staff,” says of Illinois in 1978 as vice chancellor for guidance. In every way, Ned was a class act.” a PhD that established the link between the ® emeritus professor of the University of Illinois research and dean of the graduate college. ● Based on an article written for the shell and Bohr–Mottelson models of the 150 FAST SDD Ralph Simmons. “All this was combined with In 1986, he took another extended leave to Fermilab website, news.fnal.gov. nucleus. The 1957 Peierls–Yoccoz paper Jean Yoccoz, an exemplary director for 140 continues to be regularly cited today. Having IN2P3. been appointed professor at the University 130 of Strasbourg, he continued his research first large-scale experiment to be installed Resolution (eV FWHM @ 5.9 keV) 120 0 1 2 3 4 5 Hans Jürgen Hilke 1938–2016 and in 1966 moved to Grenoble University. abroad (CELLO at DESY, Hamburg). In Peaking Time (μs) However, it was high-level scientific 1982, Yoccoz signed an agreement with then management to which Yoccoz would CERN Director-General Herwig Schopper Throughput Hans Jürgen Hilke, a true experimental constituted the world’s largest solenoid at orientate his career and invest his intellectual for the construction of the LEP linac injector 1,00,0000 that time. After many unsuccessful attempts talents to the service of our community. at the Laboratoire de l’Accélérateur Linéaire physicist and an inspirational colleague, 0.2 μs passed away on 15 October. He completed by the constructor, Hans Jürgen discovered At the end of the 1960s there was (LAL, Orsay). Yoccoz was also instrumental his diploma thesis in 1965 at Hamburg and understood the origin of these cut-offs, great debate in France concerning the in shaping a new landscape for nuclear 100,000 1 μs University, then went to CERN to develop and in a couple of days DELPHI was able to organisation of particle physics and physics with the creation of the IN2P3-CEA a bubble chamber activated by the wave take data. whether a national accelerator programme national laboratories Saturne at Saclay 4 μs pattern produced from an ultrasonic quartz From 1991 to 1994 he was deputy leader of could still be afforded. After eight years and GANIL in Caen with competitive 10,000 oscillator. Having earned his doctorate CERN’s experimental-physics division, with of unsuccessful attempts, the IN2P3 accelerators. Output Count Rate (OCR) Output Count in 1969, he soon became engaged in the particular responsibility for the mechanical institute was created in 1971 (without a We remember Jean Yoccoz as an construction of the external muon identifier and electronics engineering groups. high-energy machine) to co-ordinate and exemplary director for IN2P3. He steered 1,000 1,000 10,000 100,000 1,000,0000 for the Big European Bubble Chamber In January 1997 he joined the LHCb support research done in the many French the institute through occasionally difficult Input Count Rate (ICR) (BEBC). After completing the project and experiment, where he took over the function laboratories involved in nuclear and particle times when he had to defend its specificity having operated the detector for its first of technical co-ordinator and immediately physics. Its first director, Jean Teillac, and the need for large resources, including exposures, Hans Jürgen took a sabbatical became heavily involved in preparing immediately called on Jean Yoccoz as a highly qualified technical personnel. His at the University of California, Berkeley, Experimental physicist Hans Jürgen Hilke. various Technical Design Reports. Working deputy, and in 1975 Yoccoz became the next human qualities were recognised by all. He where he worked on time-projection in his usual energetic and passionate director – a position he held until 1983. could interact with people whatever their chambers (TPCs). While at Berkeley, he TPCs motivated Hans Jürgen to introduce manner, Hans Jürgen quickly became The early years of IN2P3 were very level in the same benevolent spirit. He knew became engaged in the most challenging this technology to the experiments at familiar with the experiment and played a important to establish an efficient structure how to listen, but his decisions were always aspect of large-TPC design, leaving his CERN’s Large Electron–Positron Collider, crucial role in strengthening its capabilities allowing laboratories to retain their firm and clear. characteristic imprint of good judgment in particular DELPHI (for which in 1980 in several areas such as the magnet, photon identities while also being integrated within In the last months of his life, Jean Yoccoz and technical prowess on the complex he became technical co-ordinator). The detectors in the ring imaging Cherenkov prioritised large projects. One of the aims was deeply affected by the loss of his Please see our web site for complete TPC read-out planes, in particular. Despite successes of the complex DELPHI detector detectors, and the muon system. He also was to achieve high visibility for French son Jean-Christophe, a mathematician specifications and vacuum applications the chaotic environment of a pioneering are in large part due to Hans Jürgen’s drive, took responsibility in financial matters and particle physicists on the international and winner of the Fields Medal who enterprise, Hans Jürgen’s unflappable and care and attention to detail. In 1989, at the safety, and undoubtedly played a significant scene, and Yoccoz’s vision turned out to died prematurely last September. Our start up of data-taking, the collaboration part in the success of the LHCb experiment. be correct. It led during his mandate to the condolences go to his family, particularly his gracious perspective was highly appreciated ® Inc. by all involved. encountered many unexplained cut-offs of Besides his scientific qualities, his integrity launching of large programmes at CERN on two sons Nigel Gilles and Serge. AMPTEK [email protected] The experience he gained in working with the superconducting magnet coils, which and honest character were always very the SPS and later on LEP, but also with the ● Michel Davier. www.amptek.com 42

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F o r advertising e n q u i r i e s , c o n ta c t CERN C o u R i E R recruitment / c l a s s i F i e d, ioP P u b l i s h i n g , te m P l e c i r c u s , te m P l e Way, b r i s t o l bs1 6hg, uK. te l +44 (0)117 930 1264 Fa x +44 (0)117 930 1178 e- m a i l s a l e s @ cerncourier . c o m P l e a s e c o n ta c t u s F o r inFormation a b o u t r at e s , c o l o u r o P t i o n s , Publication d at e s a n d d e a d l i n e s . The Faculty of Science of the University of Geneva invites applications for a position as

KEK, High Energy Accelerator FULL or ASSOCIATE PROFESSOR Research Organization in neutrino physics Call for Nomination for Next ASSIGNMENT: Director-General of KEK This full-time appointment includes teaching physics KEK, High Energy Accelerator Research Organization, invites at bachelor, master and postgraduate level as well as nominations for the next Director-General whose term will supervising master and doctoral theses. begin April 1, 2018. The candidate will develop original research at the In view of his/her role that presides over the business of KEK international level in his/her field of expertise and as a representative of the Inter-University Research Institute secure external funding. He/she will also take on Corporation, nominees shall be: organizational and administrative duties. 1) persons of noble character, with relevant knowledge and experience and having abilities to manage its educational We are seeking a candidate with a proven and research activities properly and effectively. international scientific reputation, with a wide range of skills and knowledge, including a very 2) persons expected to promote with long-term vision good understanding of the physics of neutrinos, the and strong scientific leadership, the highly advanced, Imagine taking part in the largest scientific experiment in the internationalized, and inter-disciplinary research activities ability to coordinate a research group and to initiate world. CERN needs more than physicists, engineers and of KEK by getting support from the public. communication and outreach programs for the technicians; if you are a student or a graduate just starting your University. career, or are an experienced professional - whatever your field 3) persons expected to establish and carry out the medium- of expertise, CERN could be your next opportunity. term goals and plans. REQUIRED QUALIFICATIONS: The term of appointment is three years until March 31, 2021 and shall be eligible for reappointment only twice. Thus, he/ PhD in physics or equivalent. she may not remain in office continuously over a period 9 Strong track record in research and experience in years. the management of research groups and in teaching. We widely accept the nomination of the candidates Publications in high-ranked international journals. regardless of their nationalities. We would like to ask you to recommend the best person who STARTING DATE: 01.08.2018 or upon mutual satisfies requirements for the position written above. agreement Nomination should be accompanied by: Applications including: cover letter, detailed CV 1) letter of recommendation, 2) brief personal history of the together with a list of publications, copy of highest Several PhD Positions at the Technical University of Munich (TUM) on candidate, and 3) list of major achievements (publications, degrees/diploma, research and teaching statements, academic papers, commendations and membership of Experimental and Theoretical Aspects of Neutrinos and Dark Matter list of referees who can later be contacted directly by councils, etc.). The nomination should be submitted to the the search committee. following address no later than May 31, 2017: We are looking for highly qualified and motivated We are offering PhD positions in Physics on various l Documents should be written either in English or in Recommendation letters are not requested for now. students holding an MSc or equivalent degree in experimental as well as theoretical topics on neutrino Japanese. Applications should be submitted exclusively on-line physics or astrophysics to pursue doctoral research at properties, neutrino astronomy at low and high l Forms and details are available at: https://www.kek.jp/en/ to the University website at the address the Munich School on Neutrinos and Dark Matter. energies, the particle nature of dark matter, axion NewsRoom/Release/20170301090000/ https://jobs.unige.ch before July 31st, 2017 searches, and super novae processes including the (0:00 Geneva time). The School is an Integrated Research Training Group Takayuki Sumiyoshi within the recently founded SFB1258 “Neutrinos investigation of stellar matter. The Chair of Director-General Selection Committee APPLICATIONS SENT BY EMAIL SHALL NOT BE and Dark Matter in Astro- and Particle Physics” We offer participation in running and future experiments High Energy Accelerator Research Organization (www.sfb1258.de). SFB1258 is based at the Technical like CRESST, FERMI, GERDA/LEGEND, IceCube, ACCEPTED. University of Munich (TUM) in collaboration with the IceCube-Gen2, JUNO, KATRIN, SOX, and our local Inquiries concerning the nomination should be addressed to: Complementary information may be obtained at the Max-Planck-Institut für Physik (MPP), Max-Planck- infrastructures, including the Maier-Leibnitz tandem General Affairs Division Institut für Extrater restrische Physik (MPE), Max- accelerator laboratory. General Management Department following e-mail address: [email protected]. Planck-Institut für Astrophysik (MPA), European KEK, High Energy Accelerator Research Organization Southern Observatory (ESO), and the Institut für 1-1 Oho, Tsukuba, Japan 305-0801 In a perspective of parity, applications by women are particularly Hochenergiephysik (HEPHY) der Österrei chischen For further information and application details please Tel +81-29-864-5114 Fax +81-29-864-5560 visit: http://www.sfb1258.de/graduate-school/ encouraged and welcome. Akademie der Wissenschaften. Email: kek[email protected] 44

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Senior and Junior Researchers, Postdoctoral research assistants, Bookshelf PhD students, Engineers, Physicists and Technicians at Extreme Light Infrastructure – C o m p i l e d b y V i r g i n i a g r e C o, Cern

Nuclear Physics (ELI-NP) Infinitesimal: How a Dangerous for scientific progress and the advance Mathematical Theory Shaped the Modern of thought that opened the door to the World Enlightenment. Extreme Light Infrastructure – Nuclear Physics (ELI-NP) By Amir Alexander This book is excellently written and will be a new Center for Scientific Research to be built by the IFIN-HH – ELI-NP is organizing competitions for filling One World its mathematical concepts are clearly National Institute of Physics and Nuclear Engineering the following positions: Lying midway between the history and the explained, making it fully accessible to (IFIN-HH) in Bucharest-Magurele, Romania. philosophy of science, this book illuminates a general audience. With his fascinating Senior and Junior Researchers, a fascinating period in European history narrative, the author intrigues the reader, ELI-NP is a complex facility which will host two state-of-the- Postdoctoral research assistants, during which mathematics clashed with depicting the historical background and, art machines of high performances: PhD students,Engineers/Physicists (laser engineers common thought and religion. Set in the late in particular, recounting the plots of the for 10PW lasers; control systems; contamination 16th and early 17th centuries, it describes Holy See, the Jesuits’ fight for power, the l A very high intensity laser with two 10 PW lasers; how the concept of infinitesimals – a quantity Reformation, the absolutist power of the control; particle accelerators; mechanics; optics; that is explicitly nonzero and yet smaller than kings, and the early steps of Europeans l A verycareers high intensity laser with two 10 PW lasers; A very electronic; vacuum R&D) and Technicians any measurable quantity – took a central towards democracy and freedom of thought. intense,Career brilliantopportunities γ beam, for those very with low a bandwidth,background with E γ until (vacuum systems-laser operations; vacuum R&D; role in the debate between ancient medieval The book includes extensive notes at the 19 MeV, whichin physics is obtained and related by incoherentsubjects Compton back detectors,DAQ and control systems) ideas and the new ideas arising from the end, a useful index of concepts, a timeline Renaissance. The former were represented and a “dramatis personae” section, which A bumper-sizedscattering book of with a laser helpful careerslight advice,off an real-life intense case studies, electron as well beam by immutable divine order and the principle is divided between “infinitesimalists” and (Ee>as an 700 extensive MeV) employer produced directory powered by a bywarm brightrecruits.com LINAC. of authority, the latter by social change and “non-infinitesimalists”. Finally, the images experimentation. and portraits included in the book enhance Download the free Physics World app today! The jobs description, the Candidate’s profiles and the Rules of Procedures of Selection can be found at The idea of indivisible quantities and the enjoyment for the reader. http://www.eli-np.ro/jobs.php. their use in geometry and arithmetic, which ● Pablo Fernández Martínez, CERN. had already been developed by ancient The applications shall be accompanied by the documents required in the Rules and Procedures of Selection for these positions Greek mathematicians, underwent its own The Many Faces of Maxwell, Dirac and renaissance 500 years ago, at the same time as opposition of the Jesuit mathematicians Einstein Equations: A Clifford Bundle The applications shall be sent to the Human Resources Department at [email protected]. Martin Luther launched the Reformation. The led Galileo and the “infinitesimalists” to Approach (2nd edition) consequences for mathematics and physics damnation, with irreparable consequences By Waldyr A Rodrigues Jr and Edmundo Capelas were enormous, giving rise to unprecedented for the ancient tradition of Italian de Oliveira scientific progress that continued for the mathematicians. Springer following decades and centuries. But even The second part of the book moves In theoretical physics, hardly anything is more striking is that the new way of thinking the reader to 17th century England, just better known than the Einstein, Maxwell built around the concept of infinitesimals after the English Civil War in the years of and Dirac equations. The Dirac and Fully funded PhD Studentships at the Institute of Sound crossed the borders of science and strongly Cromwell’s republic and the Restoration. In Maxwell equations (as well as the analogous and Vibration Research influenced society, up to the point that that context, the new ideas represented by Yang–Mills equations) form the basis Accelerator Division Director NSLS- II mathematics became the main focus of the infinitesimals were not only condemned by of the modern description of matter via A number of Ph.D. studentships are available at the ISVR in the area of the Anglican Church but also opposed by The NSLS-II is a state-of-the-art 3 GeV electron storage ring and cochlear mechanics and active sound and vibration control. The ISVR is a part struggle between the old and new orders. the electrodynamic, weak and strong This book is divided into two parts, each political powers. Here, the leading figure of is on course to be the world’s brightest source of synchrotron of the Faculty of Engineering and the Environment at the University of interactions, while Einstein’s equations devoted to a particular geographical area Thomas Hobbes took the stage in the fight of special and general relativity are the light. The NSLS-II will support the nation’s scientific mission by careersSouthampton and specialises in both the mechanical and medical aspects of sound and vibration, with about 40 members of academic staff, 30 and period in which this battle took place. against the indivisibles and the inductive foundations of the theory of gravity. Taken providing the most advanced tools for discovery class science in postdoctoral researchers, and 100 Ph.D. students. The first part leads the reader to late 16th method. For him, traditional Euclidean together, these three equations cover scales condensed matter and materials physics, chemistry, and biology – Career opportunities for those with a 1. Modelling the mechanics of the active cochlea century Italy, where the flourishing and geometry – which, contrary to induction, from the subatomic to the large-scale science that ultimately will enhance national and energy security background2. Active control in of physics scattered sound and related subjects creative ideas of the Renaissance had given used deduction to achieve any result from universe, and are the pillars on which the and help drive abundant, safe, and clean energy technologies. 3. Active acoustic metamaterials birth to a prolific number of mathematicians a few basic statements – was the highest standard models of cosmology and particle NSLS-II will fuel major advances in materials that will enable 4. Acoustic black holes for the control of sound and vibration and scientists. Here, the prominent figure of expression of an ordered philosophical physics are built. Although they constitute new energy technologies – such as nanocatalyst-based fuel 5.A bumper-sizedRemote sensing book strategies with for helpful active structural careers acoustic advice, control Galileo Galilei – together with Evangelista system and a model for a perfect state. core information for theoretical physicists, cells; the widespread, economical use of solar energy; the use of Applicants real-life should case have studies, at a least first as well or as upper an extensive second class degree (or an Torricelli, Bonaventura Cavalieri and Hobbes was also concerned about the threat they are rarely, if ever, presented together. high temperature superconductors in a high capacity and high equivalent standard in other qualifications approved by the university) in others – was at the forefront of the new to the principle of authority that emanated This book aims to remedy the situation physics or an engineering subject. The first studentship is available for three mathematical approach involving the from traditional mathematical thought. In by providing a full description of the Dirac, reliability electric grid; advanced electrical storage systems for employer directory powered by brightrecruits.com years at the standard EPSRC stipend rates and is open to all qualified concept of infinitesimals. This established his struggle against infinitesimals, he was Maxwell and Einstein equations. The transportation and harnessing intermittent renewable energy candidates, but will only support EU fees. 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On the opposite side, who considered mathematical knowledge expressions of these famous formulae may We are currently seeking an experienced Division Director Daley [email protected] or Dr Jordan [email protected] Cheer the religious congregation of the Jesuits used as a “down–up” inductive system in which help readers to view a given equation from to provide leadership in managing and directing the efficient To apply please use the : following link these same mathematical developments in calculus played the role of experiments new and possibly more fruitful perspectives operation of the accelerator complex. The Division Director is a www.southampton.ac.uk/engineering/postgraduate/research_degrees/apply its fight against heresy and the Reformation. in physics. Solving many of the toughest (when the Maxwell equations are written key member of the management team at NSLS-II and will report .page and select Faculty of Engineering and the Environment To them, the traditional mathematical mathematical problems of his times by in the form of the Navier–Stokes equations, directly to the NSLS-II Facility Director. Read online at physicsworld.com/careers approach was a solid basis for the absolute infinitesimal procedures, Wallis defeated for instance, they allow a hydrodynamic

truth represented by the Catholic faith traditional geometry – and Thomas Hobbes interpretation of the electrodynamic field). s For a full description of the position and its requirements and and the authority of the Pope. The fierce with it. The triumph of Wallis made way On the other hand, casting different to apply online: https://jobs.bnl.gov/ Equal Opportunity/Affirmation Action Employer and *VEVRAA Federal Contractor 47 46 74 Physics World October 2016

CCApr17_Bookshelf.indd 47 08/03/2017 15:42 Pct1lassified2-5.indd 2//21 12: CERNCOURIER www. V o l u m e 5 7 N u m b e r 3 A p r i l 2 0 1 7 CERN Courier April 2017 CERN Courier April 2017 Bookshelf Inside Story equations in similar forms may shed light He also describes the way that the ERC was on the quest for unification – as happens, for implemented and the creation of its scientific example, when the authors rewrite Maxwell’s council, discusses the “hybrid” nature of equations in Dirac-like form and use this to the ERC – being somewhere between a launch a digression on supersymmetry. programme and an institution – and the Another feature of the book concerns consequent frictions in its early days, as well On the road with the Bonn Show concepts in differential geometry that as the process to establish a procedure for are widely used in mathematics but selecting applications for funding. about which there is little knowledge in While telling the story of the ERC from theoretical physics. An example is the a critical perspective and examining its torsion of space–time: general differential challenges and achievements, the book also time-travelling through the history of manifolds are naturally equipped with offers a view of the relationship between A strong storyline and a bit of particle physics, encountering many physics a torsion in addition to the well-known science and policy in the 21st century. humour, not to mention good greats along the way who explain the physics curvature, and torsion also enters into the with the help of 25 live experiments. This description of Lie algebras, yet the torsional Synchrotron Radiation: Basics, Methods old-fashioned advertising, go a first draft was much improved in extensive completion of Einstein gravity, for instance, and Applications rehearsals. We created the character of a has been investigated very little. In the By S Mobilio, F Boscherini and C Meneghini (eds) long way when engaging new caretaker as the master of time travel, adding book, the authors take care of this issue by Springer a lighter element and bringing a common presenting the most general differential Observed for the first time in audiences with particle physics. thread to the play. We also added many geometry of space–time with curvature and 1947 – and long considered as a verbal and physical jokes to make the shows torsion. They then use this to understand problem for particle physics as it both fun and educational (the script and conservation laws, more specifically to can cause particle beams to lose detailed descriptions of the experiments can better grasp the conditions under which energy – synchrotron radiation Boarding the ferry in Puttgarden, on the small be found at arXiv:1607.07478). these conservation laws may or may not is today a fundamental tool for island of Fehmarn in northern Germany, We premiered the performance in the fail. Trivially, a genuine conservation law characterising nanostructures and advanced last September, I looked across the water to physics department at Oxford University expresses the fact that a certain quantity formalism and mathematical notation. But materials. Thanks to its characteristics in Denmark. We had two vans full of physics in March 2014. The shows in the UK went is constant over time, but in differential this is the price one has to pay for such a vast terms of brilliance, spectral range, time equipment, a minibus, 17 physics students, well, but were not full. One reason was geometry there is no clear and unambiguous and comprehensive discussion about the most structure and coherence, it is extensively one postdoc, two technicians, two professors, that schools there seem to have such a way to define an absolute time. fundamental tools in theoretical physics. applied in many scientific fields, spanning and of course the bus driver – a real entourage! tight curriculum that there is little time for As an additional important point, the book ● Luca Fabbri, INFN Bologna, Italy. material science, chemistry, nanotechnology, We were travelling to Copenhagen under excursions. We also realised that we could contains a thorough discussion about the earth and environmental sciences, biology, invitation from the Niels Bohr Institute, improve the way the shows were advertised. role of active transformations for physical Books received medical applications, and even archaeology and subsequently to Odense, to perform our For the Italy trip in 2014, I went to Padua fields (to be distinguished from passive and cultural heritage. new particle-physics show. We were road two months before and gave a colloquium transformations, which are simply a change The European Research Council The book reports the lecture notes of hardened after trips to Oxford and London in attended by all of the regional high-school in co-ordinates). Active transformations By Thomas König lessons held at the 12th edition of the the UK in 2014, and Padua and Trieste in Italy (Top) Maike Hansen and Lorenzo Ubaldi physics teachers, in addition to members are fundamental, both to define the Polity Press School on Synchrotron Radiation, held the following year. In March 2016, we even collide two boxes full of coloured balls to of the university physics department. Two transformation properties of specific fields Established in 2007 to fund in Trieste, Italy, in 2013 and organised by went to Beijing to teach Bonn-show physics show the need for bunches in the LHC beams. months later, in the department’s beautiful and also to investigate their properties from frontier-research projects, the the Italian Synchrotron Radiation Society to students at Peking University and the (Above) The wooden scattering experiment lecture hall, the shows were all packed – a purely kinematic point of view without European Research Council in collaboration with Elettra-Sincrotrone Chinese Academy of Science. Every country built in Bonn, in which the distribution of apparently only Ed Witten drew a larger involving field equations. A section is also (ERC) has quickly become a Trieste. The book is organised in four is a new physics challenge, a new adventure, scattered steel balls in the pockets at the edge crowd – and were a resounding success. devoted to exotic or new physical fields, such fundamental instrument of parts. The first describes the emission and has led to many interesting interactions. can be used to infer the shape of the Within our team the Padua performance has as the recently introduced “ELKO” field. science policy at European of synchrotron and free-electron laser Denmark, here we come! scattering centre (here triangular). taken on a mythical status for the wonderful Aside from purely mathematical level, as well as a quality standard for sources, as well as the basic aspects of The Bonn Physics Show was established rapport we had with the audience – there was treatments, the book contains useful academic research. This book traces the beamline instrumentation. In the second in 2001 with the goal of doing something a tremendous atmosphere. comments about fundamental principles history of the creation and development part, the fundamental interactions between different from the “lectures with Denmark brought further highlights. The (such as the equivalence principle) and of the ERC, drawing on the first-hand electromagnetic radiation and matter are demonstrations” format of traditional four Copenhagen performances last year physical effects (such as the Sagnac effect). knowledge of the author, who was illustrated. The third part discusses the most particle-physics shows. A big challenge for a modern were all booked out, mainly with high-school The authors also pay attention to clarifying scientific adviser to the president of the important experimental methods, including For the past 15 years we have been children. For the first time, two non-Bonn certain erroneous concepts that are ERC for four years. It covers the period different types of spectroscopy, diffraction successfully performing the Bonn show, physics show is to find students, one from Harvard and one from widespread in physics, such as assigning a between the early 2000s – when a group and scattering, microscopy and imaging mainly devoted to classical physics aimed appropriate demonstrations. Tel Aviv, were part of our team. We also nonzero rest mass to the photon. of strong-minded scientists pushed techniques. An overview of the numerous at a younger audience, and our approach has incorporated a few Bonn undergraduates. In summary, the book is well suited for the idea of allocating (more) money to applications of these techniques to various evolved with our experiences. In 2012, as part In February 2016, the DFG grant was anyone who has an interest in the differential research projects selected for the quality research fields is then given in the fourth of a large research grant from the German wooden scattering experiment (pictured). renewed for another four years. We are now geometry of twisted–curved space–time of the proposals, judged by independent, section. In this, a chapter is also dedicated to physical society (DFG), we received support We also designed our own electrically driven looking forward to more exciting trips, such manifolds, and who is willing to work on competent and impartial reviewers – and the new generation of synchrotron radiation to take a brand new particle-physics Bonn linear and circular accelerators, as well as as to Valencia and Barcelona in Spain in generalisations of gravity, electrodynamics when the first ERC programme cycle was sources, based on free-electron lasers, which show on tour that is rooted in storytelling. an experiment showing real antimatter on September. and spinor field theories (including concluded in 2013. are opening the way to new applications and A big challenge for a modern physics show stage using a β+ source, a Geiger counter and a The past 15 years have been full of exciting supersymmetry and exotic physics) from a The author is particularly interested in the more precise measurements. is to find appropriate demonstrations, since strong permanent magnet. interactions with the Bonn physics students mathematical perspective. Perhaps the only politics behind those events and shows how This comprehensive book is aimed at few real effects can be seen on stage. From For the new show, besides adding novel and with audiences in many countries. Not feature that might discourage a potential the ERC could translate into reality thanks both PhD students and more experienced our previous shows on particle physics, one experiments, we wanted to make it more only has it been rewarding in itself, it has reader, which the authors themselves to the fact that the European Commission researchers, since it not only provides an performed at CERN in French in 2010, we had like a play to better capture the audience’s stimulated and benefitted my own research acknowledge in the introduction, is the decided to support it, using a much more introduction to the field but also discusses a first set of experiments. Inspired by a simpler attention. At the end of 2013, I sat down in theoretical physics. considerable amount of sophisticated strategic, planned and technical approach. relevant topics of interest in depth. model at DESY, for example, we built a new and drafted a story that takes two heroes ● Herbi Dreiner, University of Bonn.

48 49

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CERN Courier April 2017 Delta-ti Impianti S.p.A. leader in the study, CERN Courier Archive: 1974 design and construction of technological plants for the industrial, experimental and civil fields. A l o o k b A c k t o cERN c o u R i E R v o l . 14, A p R i l 1974, c o m p i l E d b y p E g g i E R i m m E R

CERN Meeting on Technology arising from High Energy Physics CERN 392.2.74 CERN CERN 106.7.68 CERN CERN 391.10.73 CERN The water-cooled cable developed to power the magnets of the Intersecting Storage Rings. It is a high current conductor but is flexible and can be transported on a drum and cut to size where it is to be used. One problem was to design terminations where the cables join the magnets because water leakage in Construction of the electrostatic septum for Any radioactive environment prevents high voltage conditions could lead to the beam ejection system of the SPS. Its human intervention. However, breakdown. A method was evolved whereby special feature is a precisely aligned plane of conventional remote handling the lug is crimped to the cable with a thin wires individually held taut across the manipulators used in reactor and Delta-ti Impianti S.p.A. is the result of a consolidated, age-old family tradition dating back to 1925. The company has always hydraulically operated tool and then aperture where the protons pass by means radiochemical laboratories are not insulated with radiation resistant epoxy resin. of springs. On the left, the wires are already in appropriate at accelerators because of the attached particular attention to its engineering organization aimed at exploiting its great professionalism and experience throughout place. On the right, a new frame of wires is distances involved. A variant was therefore the process at best – from feasibility to preliminary studies, from executive and detail design phases down to installation, testing and From 24–26 April, CERN is the scene being positioned and the springs which will tried at the PS. of a “Meeting on Technology”. Over 300 hold them can be seen protruding below on The switch operated electric arm, commissioning for each of its plants – thereby reaffirming its primacy as a partner in experiments and research projects. participants, including industrialists, each side. mounted on a crane bridge, could travel Delta-ti Impianti S.p.A. streamlined its work by developing 2D/3D CFD simulation know-how to be applied according to special directors of applied research, senior Having a plane of wires under tension around the ring with its cables being needs and executing structural checks on its plants in compliance staff from technical universities, science avoids the possibility of distortion if a foil was automatically plugged in at connection journalists, etc, are invited to three days of used as the septum and minimises the volume boxes around the accelerator tunnel wall. Demisto Biginelli, with EN13480 e ASME standards to roll out any negative effects due founder 1925 review talks on advanced technology and of matter which is put in the way of the The manipulator is surveyed by TV to static and dynamic turbulence. the opportunity of touring 250 exhibits of protons. In the event of a wire breaking, the cameras, as seen here, and can be operated equipment and techniques. springs will pull it out of the path of the beam. up to 40 m from a plug-in box. It is Close to both French and Swiss borders, Delta-ti Impianti S.p.A. boasts a rather loyal The main purpose of CERN is to provide controlled by an operator located at the and qualified operational staff in charge of contract management and coordination, in Europe’s scientists with first class facilities for from the European high-energy physics centre of the accelerator ring. high-energy physics research. In so doing, it is programme. The emphasis will be on The prototype proved useful for many addition to highly qualified workers to monitor and execute all the works in the field, and a strong stimulus and support to the quality of straightforward presentation, without trying jobs such as remote dosimetry, beam loss certified staff for assembling activities at construction yards, duly equipped with any means physics in Europe and of science education in to anticipate possible applications. detection and dismantling radioactive they may need to achieve their goal. the European universities where most of the ● Compiled from texts on pp120–121, components. It was clear, however, that physicists using CERN are based. 126–127. higher speed and versatility was needed. A second purpose, predominant at the OUR MAIN SECTORS OF ACTIVITY INCLUDE: time of CERN’s formation 20 years ago, is the welding together of the efforts of many Compiler’s Note • Integrated systems for the production and distribution of energy (combined cycle power plants and cogenerating power plants) Amid the turmoil of today’s world, CERN continues to fulfil the mission European countries to work for common • Pipelines in general (overheated water, steam, compressed air, oil and fuels, natural gas, etc.) enshrined in its 1954 Convention. The lab now has an impressive aims. This purpose remains valid today and • Cooling Plant • HVAC • Fire protection plants • Electrical and electroinstrumental plants administrative infrastructure for knowledge transfer across a broad front, also seems well fulfilled. • District heating networks and substations. However, a great deal of advanced from high-school teacher training to high-tech industrial collaboration. In technology is involved in carrying out addition, a regular series of exhibitions are organised whereby industries high-energy physics and, although knowledge showcase their products at CERN and interact with in-house experts of CERN’s work is freely available, not much and clients. While spin-off into nuclear medicine and global networking has so far been done to project this knowledge is well known, the images shown here are some examples of the kind to people who could find it useful. of pioneering techniques, rather than technologies, that can also find In the April meeting, a kind of applications beyond the laboratory. “technological accounting” exercise, CERN will spread out some of the achievements reliability by tradition www.lineadue-at.it 10098 Rivoli (Torino) Italy – via Albenga 92 - Tel +39 (0)119571597 CANNES (06150) - 13, Rue Roquebilliere - Tel +33(0)422460744

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5 V i ew p o i n t 15 S c i e n cew a t c h 31 Exotic hadrons bend the rules Half a century after the quark model was devised, a number of 7 N ew s 16 A s t r ow a t c h hadrons appear to challenge its axioms. But are they truly exotic? • Sri Lanka signs International Co-operation Agreement with 37 F a ce s & P l a ce s CERN European computing cloud takes off Milestone for US F e a t u r e s • • 18 The two-loop explosion dark-matter detector • European organisations uphold scientific 44 R ec r u i t me n t values • Chamonix event prepares for LHC’s future • CMS NNLO calculations keep pace with precision of LHC experiments. 47 B oo k s h elf undergoes tracker transplant • ATLAS reveals more strangeness in 23 Looking forward to photon–photon physics the proton • ALICE measures shape of the QGP fireball at freeze- Detectors will probe the quartic couplings of electroweak bosons. out • Rare decay puts Standard Model on the spot • BaBar casts 49 I n s i d e S t o r y further doubt on dark photons 26 A 30-year adventure with heavy ions 50 A r c h i ve Heavy-ion physics could be about to enter a new paradigm.

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