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WELCOME V OLUME 5 7 N UMBER 1 J ANUARY /F EBRUARY 2 0 1 7 CERN Courier – digital edition Welcome to the digital edition of the January/February 2017 issue of THE GRAVITY ISSUE CERN Courier.

The detection of gravitational waves by the twin aLIGO detectors, announced in February last year, is one of the most significant discoveries in physics for decades. It is also further spectacular confirmation of Einstein’s theory of gravity, general relativity. Although the existence of gravitational waves had already been established from precise measurements of pulsars, their direct detection by interferometers opens a new vista on the universe. This issue of CERN Courier explores what we can expect from the new era of gravitational-wave astronomy, from understanding the internal machinery of black holes to probing the very early universe, and describes the remarkable technological feat that enabled aLIGO to detect a displacement 200 times smaller than the proton radius. We also survey the broader experimental status of general relativity, which enters its second century without any signs of cracking. Upcoming experiments at CERN’s Antiproton Decelerator are about to test the gravitational free-fall of antiatoms, while searches for extra dimensions at the Large Hadron Collider continue to place tight constraints on more exotic models of gravity. Despite being the first force to be tamed by mathematics, gravity is still riddled with enigmas. Dark energy and dark matter are among them, but perhaps the deepest mystery of all is how gravity relates to the other three forces – a challenge that has outfoxed the best minds for the best part of a century.

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To subscribe to the magazine, the e-mail new-issue alert, please visit: SURF’S UP ANTI-SPECTROSCOPY http://cerncourier.com/cws/how-to-subscribe. ENLARGEMENT Strong-fi eld Antihydrogen reveals its colours p8 milestone for STRATEGY EDITOR: MATTHEW CHALMERS, CERN AWAKE experiment CERN reinforces its long-term DIGITAL EDITION CREATED BY DESIGN STUDIO/IOP PUBLISHING, UK p8 scientifi c aspirations p5

CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 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 1 J a N u a r y /F e b r u a r y 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 Luis Alvarez-Gaume, Peter Jenni, Christine Sutton, Claude Amsler, 7 n E W s Roger Bailey, Philippe Bloch, Roger Forty India to become associate Member State Slovenia to Laboratory correspondents: • • Argonne National Laboratory (US) Tom LeCompte become associate Member State in pre-stage to membership Brookhaven National Laboratory (US) Achim Franz • Cornell University (US) D G Cassel Antihydrogen atoms show their colour • AWAKE makes waves DESY Laboratory (Germany) Till Mundzeck Proton–lead run tops record year of LHC operations ATLAS EMFCSC (Italy) Anna Cavallini • • Enrico Fermi Centre (Italy) Guido Piragino makes precision measurement of W mass Run 2 promises a Fermi National Accelerator Laboratory (US) Katie Yurkewicz • Forschungszentrum Jülich (Germany) Markus Buescher harvest of beauty for LHCb ALICE zeroes in on cold-matter GSI Darmstadt (Germany) I Peter • IHEP, Beijing (China) Tongzhou Xu effects Protons probe quark–gluon plasma at CMS Electron IHEP, Serpukhov (Russia) Yu Ryabov • • INFN (Italy) Antonella Varaschin gun shrunk to matchbox size Jefferson Laboratory (US) Kandice Carter JINR Dubna (Russia) B Starchenko KEK National Laboratory (Japan) Saeko Okada 13 s CiEnCEWatCh Lawrence Berkeley Laboratory (US) Spencer Klein Los Alamos National Laboratory (US) Rajan Gupta NCSL (US) Ken Kingery 15 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 16 The dawn of a new era Science and Technology Facilities Council (UK) Jane Binks SLAC National Accelerator Laboratory (US) Farnaz Khadem Gravitational waves open a profound new vista on nature. TRIUMF Laboratory (Canada) Marcello Pavan

Produced for CERN by IOP Publishing Ltd 21 General relativity at 100 IOP Publishing Ltd, Temple Circus, Temple Way, Bristol BS1 6HG, UK Testing Einstein’s masterpiece with ever increasing precision. Tel +44 (0)117 929 7481

Publisher Susan Curtis 27 Gravity’s quantum side Production editor Lisa Gibson Technical illustrator Alison Tovey Quantum gravity continues to confound theorists. Group advertising manager Chris Thomas Advertisement production Katie Graham The LHC’s extra dimension Marketing & Circulation Angela Gage 31 Searches at ATLAS and CMS constrain models of extra dimensions. Head of B2B & Marketing Jo Allen Art director Andrew Giaquinto 34 Catching a gravitational wave Advertising Tel +44 (0)117 930 1026 (for UK/Europe display advertising) The technology behind LIGO’s epochal discovery. or +44 (0)117 930 1164 (for recruitment advertising); E-mail: [email protected]; fax +44 (0)117 930 1178 39 Does antimatter fall up? General distribution Courrier Adressage, CERN, 1211 Geneva 23, Switzerland E-mail: [email protected] CERN experiments to test the free-fall of antiatoms. 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 41 The many lives of supergravity E-mail: [email protected] Germany Antje Brandes, DESY, Notkestr. 85, 22607 Hamburg, Germany 40 years at the forefront of attempts to unify nature’s forces. E-mail: desypr@desy.de UK Mark Wells, Science and Technology Facilities Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1SZ 45 Linking waves to particles E-mail: [email protected] Gravitational waves could also shed light on the microscopic world. 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, 49 F a C E s & p L a C E s St Charles, IL 60174, US • New standard for industry and science • Precision current measuring transducers with 58 E C r u i t M E n t closed-loop current transformer technology (Zero Published by European Organization for Nuclear Research, CERN, r • Infrastructure for management of Rear Transition 1211 Geneva 23, Switzerland Flux technology) Tel +41 (0) 22 767 61 11. Telefax +41 (0) 22 767 65 55 Module (RTM) boards 63 B O O k s h E L F Printed by Warners (Midlands) plc, Bourne, Lincolnshire, UK • Custom design solutions • Galvanic isolation between primary and secondary conductor © 2017 CERN ISSN 0304-288X 66 a r C h i V E • Current-Output and Voltage-Output versions available

On the cover: Newton’s apple, an icon for gravity. (Image credit: Graphic treatment by Mathew Ward.)

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CernCourier_January_2017.indd 1 03/01/17 17:17 CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 Mass spectrometers for vacuum, gas, plasma and surface science CERN Courier January/February 2017 Viewpoint Instruments for Advanced Science Unity through global science CERN’s enlargement policy will help particle physics adapt to an evolving global environment.

associate members. Late last year, agreements with Slovenia for associate membership in the pre-stage to

M Brice/CERN membership and with India for associate membership QGA were signed (see p7). Brazil, Croatia, Lithuania and Precision Gas Analysis Russia have also applied for associate membership. CERN builds on a long tradition of a global Instruments for residual gas analysis (RGA) engagement. The Organization has formal relations with non-member states (NMS) via bilateral Evolved gas analysis International Co-operation Agreements (ICAs), TPD/TPR currently in force with 47 countries. Out of a total of about 12,700 users at CERN, the participation of Vacuum process monitoring NMS users is now almost 40% – the majority of which are researchers from the US and Russia working on the LHC. The overall NMS participation in the non-LHC research programme is currently about CERN’s geographical By Emmanuel Tsesmelis 20%. Financial resources for research programmes, enlargement policy of 2010 notably maintenance and operation costs for the LHC has been turned into a CERN’s Large Hadron Collider (LHC) and its experiments, are shared between the Member States, strategy to help secure the discovery of the Higgs boson in 2012 have launched the associate members and the NMS. In addition, long-term future of particle a new era of research in particle physics. The LHC there is increasing interest in collaboration on New Aff ordable Compact COMPACT SIMS physics. and its upgrades will chart the course of the field accelerator R&D and related technologies, focusing NEW for many years to come, and CERN is therefore in a on the LHC’s luminosity upgrades and also on the unique position to help shape the long-term future of FCC and CLIC studies. The number of states involved SIMS Instrument particle physics. In view of this, CERN is exploring two in such activities is already growing beyond the different and challenging projects: the Compact Linear restricted circle of NMS that contributed to the LHC for depth profile & interface analysis. Collider (CLIC) and a Future Circular Collider (FCC). accelerator construction. The increasingly global Small footprint These developments are taking place at a time interest in CERN also translates into a rising demand when facilities for high-energy physics, as for for CERN’s education and training programmes Positive SIMS and SNMS other branches of science, are becoming larger and – falling within CERN’s mission of helping build Depth Profiling more complex as well as requiring more resources. capacity in countries that are developing their Funding for the field is not increasing in many particle-physics communities. 3D characterisation and imaging countries and the timescale for projects is becoming The geographical enlargement policy of 2010 Isotopic analysis longer, resulting in fewer facilities being realised. offers important opportunities for the future of the Particle physics must adapt to this evolving reality by Organization. Now, CERN has developed it into Analysis on the nanometre scale fostering greater co-ordination and collaboration on a strategy, presented to Council in March 2016, to a global scale. This goes hand in hand with CERN’s ensure that geographical enlargement consolidates tradition of networking with worldwide partners. the institutional base and thus reinforces the long-term In 2010, CERN Council approved a radical shift scientific aspirations of CERN. Enlargement is EQP in CERN’s membership policy that opened full not an aim in and of itself. Rather, the focus is on Plasma Characterisation membership to non-European states, irrespective of strengthening relations with countries that can bring their geographical location. At the same time, Council scientifi c and technological expertise to CERN and EQP ion mass and energy analyser introduced the status of associate membership to can, in turn, benefi t from closer engagement. RF, DC, ECR and pulsed plasma facilitate the accession of new members, including It is essential that membership and associate countries outside of Europe that might not command membership are beneficial to particle physics in Neutrals and neutral radicals suffi cient resources to sustain full membership CERN( individual countries, and that governments continue Time resolved analysis Emmanuel Courier December 2014 p58). to invest in the growth of national communities. At Tsesmelis is an Geographical enlargement is part of the effort to the same time, enlargement should not hinder the HPR-60 extends analyses to atmospheric experimental secure the future of the laboratory, and the process has operational effi ciency of the laboratory. CERN’s pressure processes particle physicist been gradual and measured. Israel became CERN’s engagement with prospective members and who is head of 21st Member State in 2014 while Romania joined as associate members is clearly oriented towards these relations with associate Member the 22nd Member State in 2016. Cyprus and Serbia objectives, mindful that investigating the unifi cation States and non-Member States at are presently associate members in the pre-stage to of the fundamental forces of nature requires uniting CERN. (Image credit: CERN.) membership, while Pakistan, Turkey and Ukraine are scientifi c efforts on a global scale.

5 W www.HidenAnalytical.com E [email protected]

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High Vacuum Pumps i ntErnatiOnaL India to become associate Member State

On 21 November, CERN signed an CERN agreement with Sekhar Basu, chairman of CERN Director-General the Atomic Energy Commission (AEC) Fabiola Gianotti and secretary of the Department of Atomic (left) signs the Energy (DAE) of the government of India, to agreement with admit India as an associate Member State. Sekhar Basu. India has been a partner of CERN for more than 50 years, during which it has made substantial contributions to the construction of the LHC and to the ALICE and CMS experiments, as well as Tier-2 centres for the Worldwide LHC Computing Grid. A co-operation agreement was signed in 1991, but India’s relationship with BICOM_13622.02 1.08.2016

© CERN goes back much further, with Indian India also participates in the COMPASS, for staff appointments. “Becoming institutes having provided components ISOLDE and nTOF experiments at CERN. associate member of CERN will enhance for the LEP collider and one of its four In recognition of these substantial participation of young scientists and detectors, L3, in addition to the WA93 and contributions, India was granted observer engineers in various CERN projects and WA89 detectors. The success of the DAE– status at CERN Council in 2002. When it bring back knowledge for deployment in CERN partnership regarding the LHC has enters into force, associate membership the domestic programmes,” says Basu. “It also led to co-operation on novel accelerator will allow India to take part in CERN will also provide opportunities to Indian technologies through DAE’s participation Council meetings and its committees, industries to participate directly in CERN in CERN’s Linac4, SPL and CTF3 projects. and will make Indian scientists eligible projects.” Slovenia to become associate Member State Sommaire en français TURBOVAC L’Inde sur le point de devenir État membre 7 in pre-stage to membership associé du CERN Turbomolecular pumps from the TURBOVAC i(X) La Slovénie sur le point de devenir État 7 CERN Council has voted unanimously to line with integrated electronic drive will allow you to membre associé du CERN en phase préalable admit the Republic of Slovenia to associate optimize pump-down times and consistently hit your à l’adhésion membership in the pre-stage to CERN target regarding pressures and gas flows. membership. Slovenia’s membership will L’antihydrogène dévoile sa couleur 8 facilitate, strengthen and broaden the Designed to offer the best performance-size ratio AWAKE fait des vagues 8 participation and activities of Slovenian available in the ISO 63/100/160 size range, they feature scientists, said Slovenian minister Maja Exploitation du LHC : des collisions 9 a rotor and drag stage design to achieve maximum Makovec Brenčič, and give Slovenian proton-ion viennent couronner une performance and unparalleled speed, especially for industry full access to CERN procurement Maja Makovec Brenčič, Slovenian minister année record orders. “Slovenia is also aware of the CERN of education, science and sport (left), signs light gases. ATLAS réalise des mesures précises de la 10 offerings in the areas of education and public the agreement with CERN Director-General outreach, and we are therefore looking Fabiola Gianotti on 16 December. masse du W New Turbomolecular pump range forward to become eligible for participation L’exploitation 2 promet une récolte de toute 10 in CERN’s fellows, associate and student co-operation agreement, and in 2009 Slovenia beauté pour LHCb 90 l/s - 450 l/s programmes.” applied to become a Member State. Slovenian physicists have participated Following internal approval procedures, ALICE vise les effets liés à la matière froide 11 in the LHC’s ATLAS experiment for the Slovenia will join Cyprus and Serbia as an Des protons pour sonder le plasma 11 past 20 years, focusing on silicon tracking, associate Member State in the pre-stage quarks-gluons à CMS protection devices and computing at the to membership. At the earliest two years Slovenian Tier-2 data centre. However, thereafter, Council will decide on the Un canon à électrons de la taille d’une boîte 12 Slovenian physicists contributed to CERN admission of Slovenia to full membership. d’allumettes long before Slovenia became an independent “It is a great pleasure to welcome Slovenia Lier son et signifi cation 13 Leybold GmbH state in 1991, participating in an experiment at into our ever-growing CERN family as an Bonner Str. 498 · D-50968 Köln LEAR and the DELPHI experiment at LEP. In associate Member State in the pre-stage to La lumière des étoiles polarisée par le vide 15 quantique ? T +49 (0) 221-347-0 1991, CERN and the Executive Council of the membership,” says CERN Director-General F +49 (0) 221-347-1250 Assembly of the Republic of Slovenia signed a Fabiola Gianotti. [email protected] www.leybold.com 7

LV_Anz_TMPi_X_V3a_EN_PW_213x282.indd 1 05.08.16 13:09 CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 News News

a n t i M a t t E r et al. et L Pang motivations for CERN’s Antiproton Powerful supercomputer simulations of The international team responsible for the Antihydrogen Decelerator (AD), since it offers an colliding atomic nuclei have provided work, which involved weeks of processing

extraordinary new tool to test whether matter new insights about quark–gluon plasma on a GPU cluster, suggests that longitudinal Rev. Lett. Phys. 2016 M Brice, CERN behaves differently from antimatter and thus (QGP), a superhot fl uid of de-confi ned spin correlations can be used to study the atoms show test the robustness of the Standard Model. partons produced in heavy-ion collisions vortex structure of the expanding QGP in The ALPHA collaboration, which expects to at the LHC and at RHIC, Brookhaven high-energy heavy-ion collisions. Different their colour improve the precision of its measurements, National Laboratory. Shown in the from global transverse polarisation, the

generates roughly 25,000 antihydrogen image are the transverse (arrows) longitudinal spin correlation does not 117

atoms per trial by mixing antiprotons from and longitudinal vorticity (contour) decrease with beam energy or vanish in event 192301 the AD with positrons. Around 14 antiatoms distributions of a strongly coupled quark– averages. This provides a unique opportunity Following 20 years of research and per trial are trapped and interrogated by gluon plasma in the transverse plane at to study the local fl uid vorticity of the QGP at development by the CERN antimatter a laser at a precisely tuned frequency to forward spatial rapidity. The coupling LHC energies, concludes the team. “We can community, the ALPHA collaboration has ALPHA uses a laser system to interrogate measure their internal states. between spin and local vorticity shifts think about this as opening a completely new reported the fi rst ever measurement of the the electronic states of antihydrogen. Low-energy antihydrogen was fi rst the energy level of fermions, leading to window of looking at quark–gluon plasmas, optical spectrum of an antimatter atom. The synthesised by the ATHENA collaboration different phase-space distributions for and how to study them,” says team member result, published in Nature in December, invariance requires that antihydrogen has in 2002, later repeated by the ATRAP, fermions with different spin states and Xin-Nian Wang at the Central China Normal involves technological developments that exactly the same spectrum. ALPHA and ASACUSA collaborations, therefore spin polarisation along the University and Lawrence Berkeley National open a completely new era in high-precision The ALPHA team has now succeeded in and ALPHA trapped the fi rst antihydrogen direction of the local vorticity. Laboratory. antimatter research. observing the fi rst spectral line in an atom of atoms in 2010. The new result, along with Comprising a single electron orbiting antihydrogen, made up of an antiproton and recent limits on the antiproton–electron a single proton, hydrogen is the simplest a positron. The measurement concerned the mass ratio by the ASACUSA collaboration L h C n E W s and most well-understood atom, and has 1S–2S transition, which has a lifetime on the and antiproton charge-to-mass ratio by the played a central role in fundamental physics order of a tenth of a second and therefore leads BASE collaboration, demonstrates that tests Proton–lead run tops record year of LHC operations for more than a century. Its spectrum is to a narrow spectral line that is particularly of fundamental symmetries with antimatter characterised by well-known spectral lines suitable for precision measurements. The at CERN are maturing rapidly. at certain wavelengths, corresponding to the measurement was found to be in agreement On 26 October, the LHC completed its 2016 200 and the LHC delivered pPb collisions at ● Further reading ) CMS 2016 –1 emission of photons when electrons jump with the hydrogen spectrum, and therefore proton–proton operations at a collision energy ATLAS 2016 an energy of 8.16 TeV. This is the highest between different orbits. Measurements consistent with CPT invariance, with a ALPHA Collaboration 2016 doi:10.1038/ of 13 TeV, during which it exceeded the design energy ever produced by a collider for such × –10 nature21040. of the hydrogen spectrum agree with the relative precision of around 2 10 . value of the luminosity and broke many other 150 an asymmetric system, and included a short predictions of quantum electrodynamics Comparing the spectra of hydrogen and ASACUSA Collaboration 2016 Science 354 610. records (CERN Courier December 2016 run for the LHCf experiment and also a third at the level of a few parts in 1015, and CPT antihydrogen was one of the main scientifi c BASE Collaboration 2015 Nature 524 196. p5). As in most years, the machine was then run in which the directions of the Pb and p reconfi gured for a month-long heavy-ion beams were reversed. Thanks to the superb C C E L E r a t O r t E C h n O L O G Y 100 minimum bias a run, devoted this year to colliding beams of at 5.02 TeV beam reversal performance of the injectors and numerous A Petrenko/CERN protons (p) and lead nuclei (Pb). Following in 2016 and LHCf run improvements in the LHC, the luminosity AWAKE makes waves a feasibility test in 2012 and an initial soared to 9 × 1029 cm–2 s–1, which is 7.8 times 50 month-long run in 2013, pPb collisions remain ATLAS/ CMS/ ALICE 2016 the design value set some years ago. The ALICE 2013 a novel mode of operation at the LHC. Despite LHCb 2016 luminosity could have been pushed even In early December, the AWAKE collaboration this novelty, the LHC team was able to deliver LHCb 2013 further had the intense fl ux of lead beam made an important step towards a pioneering enormous data sets to the experiments for the integrated proton–nucleus luminosity (nb 0 fragments from the collisions not risked 012 34 accelerator technology that would reduce the investigation of extreme nuclear matter during time (weeks from start of physics) quenching nearby magnets. On 4 December, size and cost of particle accelerators. Having the 2016 run. the LHC was switched back to 5.02 TeV for a commissioned the facility with fi rst beam Asymmetric proton–nucleus collisions Integrated luminosity versus time since the fi nal 20 hours of pPb data taking, delivering in November, the team has now installed a were originally seen as a means to start of physics, comparing the 2013 run at a further 120 million minimum-bias events plasma cell and observed a strong modulation disentangle cold from hot nuclear-matter 5.02 TeV (dashed lines) with the 8.16 TeV for ALICE. of high-energy proton bunches as they pass effects studied in lead–lead collisions. part of the 2016 run (solid lines). That such a complex run could be through it. This signals the generation of Surprisingly, a more complex picture implemented in such a short time was a very strong electric fi elds that could be used emerged following the pPb results of 2012 to increase an earlier collected sample of triumph for the LHC and all those concerned to accelerate electrons to high energies over and 2013. For 2016, the LHC experiments minimum-bias events. The other experiments with its design, construction and operation. short distances. Comparison of the proton-bunch longitudinal profi le (left, no plasma) with the profi le for a requested a variety of apparently also participated, with LHCb studying Every one of the high-priority goals, plus AWAKE (Advanced Proton Driven bunch passing through plasma (right), showing the strong modulation of the bunch. incompatible operating conditions, collisions between protons and a target of some subsidiary ones, for ATLAS, CMS, Plasma Wakefi eld Acceleration Experiment) according to their diverse capabilities and helium gas. As foreseen, the beam lifetimes ALICE and LHCb were comfortably is the fi rst facility to investigate the use of fi rst experiment to use protons as a driver – is a major challenge. The next step for the physics programmes. Careful analysis of the were extremely long, allowing seven days of exceeded. CMS recorded an integrated plasma wakefi elds driven by proton beams. which, given the high energy of the SPS, can AWAKE collaboration is to inject a second beam physics and operational requirements nearly uninterrupted running at a constant luminosity of nearly 200 nb–1 at 8.16 TeV, The experiment involves injecting a “drive” drive wakefi elds over much longer distances beam of electrons, the “witness” beam, led to an ambitious schedule comprising levelled luminosity of 0.8 × 1028 cm–2 s–1. A representing a six-fold increase of the sample bunch of protons from CERN’s Super Proton compared with electron- or laser-based which is accelerated by the wakefi eld just three different beam modes that could total of 660 million minimum-bias events collected from the fi rst pPb run in 2013 at Synchrotron (SPS) into a 10 m-long tube schemes,” says AWAKE spokesperson Allen as a surfer accelerates by riding a wave. “To potentially fulfi l all requests. were collected, increasing by a factor six the 5 TeV, and allowing the collaboration to containing a plasma. The bunch then splits Caldwell of the Max Planck Institute for have observed indications for the fi rst time Following a technical stop, the fi rst set-up data set from 2013. One of the fi rst fi lls also investigate the behaviour of hard probes in into a series of smaller bunches via a process Physics in Munich. of proton-bunch self-modulation, after just a for pPb collisions at a centre-of-mass energy turned out to be the longest LHC fi ll ever, high-multiplicity pPb collisions (see article called self-modulation, generating a strong While it has long been known that plasmas few days of tests, is an excellent achievement. for colliding nucleon pairs of 5.02 TeV started lasting almost 38 hours. on p11). ATLAS recorded a similar data set, wakefi eld as they move through the plasma. may provide an alternative to traditional It’s down to a very motivated and dedicated on 5 November and physics data-taking Just one day after the 5.02 TeV run while ALICE and LHCb each received totals “Although plasma-wakefi eld technology has accelerating methods based on RF cavities, team,” says Edda Gschwendtner, CERN started on 10 November. This run was mainly ended, the second set-up involving new well over 30 nb–1 at 8.16 TeV in the two beam been explored for many years, AWAKE is the turning this concept into a practical device AWAKE project leader. dedicated to the LHC’s ALICE experiment high-luminosity beam optics was complete directions.

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L h C EXpEriMEnts B– → D 0K*– decays. While B – → D 0K– decays the detector performs better than in Run 1. with charged and neutral B-meson decays have been extensively studied in the past, this Although the statistical uncertainty on γ and a variety of D-meson fi nal states, all is the fi rst time the B– → D 0K*– mode has been from this measurement alone is still large, the performed with Run 1 data, yielded a central ATLAS makes precision measurement of W mass investigated. The analysis, fi rst presented sensitivity will be improved by the addition value of 72±7 degrees. LHCb’s ultimate aim, at CKM2016 (see p52), allows the LHCb of more data, as well as by the use of other following detector upgrades relevant for A precise was achieved via the large sample of Z-boson collaboration to cross-check expectations D-meson decay modes. This bodes well for LHC Run 3, is to determine γ with a precision measurement of ATLAS preliminary events and the precise knowledge of the for the increase of signal yields in Run 2 future measurements of γ to be performed in below 1°, providing a powerful test of the LEP comb. 33 MeV±80376 the mass of the mw Z mass. Accurate predictions of the W-boson using real data. A signifi cant increase, this and other decay modes with the full Run 2 Standard Model. stat. uncertainty W boson, which Tevatron comb. full uncertainty 16 MeV±80387 production and decay properties are also roughly corresponding to a factor three, is data set. was discovered at CERN in 1983, is vital crucial at a proton–proton collider. The observed per unit of integrated luminosity. Measurements of the angle γ are of great ● Further reading because it is closely related to the masses LEP + Tevatron 15 MeV±80385 enhanced amount of heavy-quark-initiated This demonstrates that the experiment has importance because it is the least well-known LHCb Collaboration 2016 LHCb-PAPER-2016-032, of the top quark and the Higgs boson. 19 MeV±80370 production and the ratio of valence and sea benefi tted from the increase in b-production angle of the unitarity triangle. The latest arXiv:1611.03076. ATLAS Measuring the W mass tests this prediction quarks in the proton affect the W boson’s cross-section, but also that the trigger of combination from direct measurements LHCb Collaboration 2016 LHCb-CONF-2016-014. 8 MeV±80358 and thus the self-consistency of the electroweak fit transverse-momentum distribution and its Standard Model (SM), since any deviation polarisation, which makes the measurement from theory would be a sign of new physics. 80250 80300 80350 80400 80450 sensitive to the parton distribution functions ALICE zeroes in on cold-matter effects The W mass was measured previously at mw (MeV) of the proton. To address these issues, CERN’s Large Electron–Positron (LEP) ATLAS combined the most advanced collider and Fermilab’s proton–antiproton ATLAS measurement of the W mass is theoretical predictions with experimental Measuring the production collider, the Tevatron, yielding a world compared to the SM prediction from the constraints from precise measurements of cross-section of charm hadrons ALICE pp, √s = 7 TeV p–Pb, √s NN = 5.02 TeV average of 80.385±0.015 GeV, which is electroweak fi t, and to the combined values Z- and W-boson differential cross-sections in proton–proton collisions 1.6 prompt D mesons, –0.96 < ycms < 0.04 consistent with the SM constraints of measured at LEP and at the Tevatron and of Z-boson transverse momentum and provides an important test 2 0 10 prompt D , |y| < 0.5 average D0, D+, D*+ c) 80.358±0. 0 08 G eV. collider. polarisation. of perturbative quantum 0 –1 ALICE D 1.2 The ATLAS collaboration has now Future analysis of larger data samples chromodynamics (QCD). In proton– FONLL

reported the fi rst measurement of the challenging at the LHC compared with at the LHC would allow the reduction of nucleus collisions, “cold-matter” effects b GeV GM-VFNS μ 10 LO kT fact pPb W mass at the LHC, based on proton–proton LEP and the Tevatron because there are the statistical uncertainty and of several related to the presence of nuclei in the R dy) ( collisions at a centre-of-mass energy of a large number of interactions per beam experimental systematic uncertainties. colliding system are expected to modify T 0.8

7 TeV (corresponding to an integrated crossing and signifi cant contributions to Finally, a better knowledge of the parton the production cross-section and the /(dp 1 –1 σ colour glass condensate 2

luminosity of 4.6 fb ). The measured value, W production from second-generation distribution functions and improved QCD transverse-momentum distribution of d pQCD NLO with CTEQ6M+EPS09 PDF 80.370±0.019 GeV, matches the precision quarks (strange and charm). ATLAS and electroweak predictions of W- and open-charm hadrons. Assessing such 0.4 ± 3.5% lumi, ± 1.3% Vitev et al.: cold-nuclear-matter effects of the best single-experiment measurement measured the W mass by reconstructing the Z-boson production are crucial to further effects is thus crucial for interpreting the –1 BR uncertainty not shown Duke transport model of the W mass performed by the Tevatron’s kinematic properties of leptonic decays, in reduce the theoretical uncertainties. results from heavy-ion collisions, where 10 POWLANG transport model CDF experiment, and is consistent with which a W produces an electron or muon and a hot and dense medium of deconfi ned 04812 16 0 p (GeV/c) ● Further reading T 0 10 20 both the SM prediction and combined a neutrino in the fi nal state. partons – the quark–gluon plasma (QGP) – p (GeV/c) measurements (see fi gure). The analysis required a highly accurate ATLAS Collaboration 2016 CERN-EP-2016-305 & is formed. T Measuring the W mass is more calibration of the detector response, which ATLAS-CONF-2016-113. Previously, ALICE measured D-meson The cross-section for open-charm production in proton–proton data (left) agrees within production in proton–lead collisions and uncertainties with three different perturbative QCD calculations. The nuclear modifi cation found no substantial modifi cation relative factor RpPb (right) is compatible with unity within uncertainties, indicating that Run 2 promises a LHCb preliminary to proton–proton interactions within cold-nuclear-matter effects are small in this kinematic range. – 0 – 200 B → D K* the kinematic range of the measurement – * *– harvest of beauty B → D (Dγ)K (0) (covering a transverse momentum, p T, proton collisions at 7 TeV and in proton– The current precision of the measurement – – ) → * * 2 B D (Dγ)K (±1) between one and 24 GeV/c at mid-rapidity). lead collisions at 5.02 TeV. In contrast to does not yet confi rm the role of the different – 0 – B → D* (Dπ )K* (0) – 0 – Most cold-nuclear-matter effects are previous ALICE publications, the analysis nuclear effects or the possible presence of for LHCb B → D* (Dπ )K* (±1) 0 – – expected to modify charm production at relied on estimating and subtracting the additional hot-medium effects. However, B → D* (Dπ )K* (0) 0 – – → * * low p T, but no measurement of D-meson combinatorial background without having applied to larger data sets in the future, the 100 B D (Dπ )K (±1) 0 combinatorial production down to zero transverse to reconstruct the D decay vertex. This analysis technique will provide insight into 0 The fi rst b-physics analysis momentum was performed at mid-rapidity at allowed the fi rst measurement of the D the physics-rich region close to pT = 0. using data from LHC LHC energies. signal in the interval 0 < pT < 1 GeV/c and a

Run 2, which began in (7.0 MeV/c candidates/ Recently the ALICE collaboration signifi cant reduction of the uncertainties in ● Further reading 0 2015 with proton–proton extended the measurement of the D -meson the interval 1 < pT < 2 GeV/c compared with ALICE Collaboration 2014 Phys. Rev. Lett. 113 232301. collisions at an energy of 13 TeV, shows 0 cross-section down to zero p T in proton– previous results. ALICE Collaboration 2016 arXiv:1605.07569. great promise for the physics programme 4900 5100 5300 5500 of LHCb. During 2015 and 2016, the m(DK*) (MeV/c2) experiment collected a data sample Protons probe quark–gluon plasma at CMS corresponding to an integrated luminosity The new measurement concerns the process B– → D0K*– (red), where the D 0 decays into of about 2 fb–1. Although this value is two-body fi nal states consisting of charged π and/or K mesons. The powerful background Proton–nucleus collisions be too small and dilute to themselves form Subsequent studies have supported the smaller than the total integrated luminosity suppression of the LHCb detector allows the signal to be isolated with extremely high purity. provide a crucial tool to a QGP, they have served as a reference hypothesis that a dense, QGP-like medium collected in the three years of Run 1 (3 fb–1), investigate the quark–gluon in the search for QGP signatures in the may be formed in high multiplicity pPb the signifi cant increase of the LHC energy particle-identifi cation capabilities. Once doubled the statistics of beauty particles on plasma (QGP), a state of collisions of two heavy ions. Nonetheless, systems. However, several key signatures in Run 2 has almost doubled the production such an increase is taken into account, along tape with respect to Run 1. nuclear matter with a high in the fi rst-ever pPb collisions at the LHC, of a dense QGP medium, observed in cross-section of beauty particles. with improvements in the trigger strategy The new analysis is based on 1 fb–1 of energy density spread over a relatively collected in 2013, the CMS experiment PbPb collisions, remain unestablished

Furthermore, the experiment has improved and in the particle identifi cation of the available data, aiming to measure the large volume. Although proton–lead (pPb) observed QGP-like features in very high for pPb events. These unestablished ▲ the performance of its trigger system and experiment, LHCb has already more than angle γ of the CKM unitarity triangle using collision systems have been considered to multiplicity pPb events. signatures include the loss of energy

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C OMPILED BY J OHN S WAIN , N ORTHEASTERN U NIVERSITY Linking sound with meaning

A study of nearly two thirds of the world’s Words for “tongue” tend to contain the 6000+ languages has revealed widespread letters i or u, “round” often appears with r, associations between the sounds of words and “small” with i. and their meanings. It has long been known that when people are shown pictures of associations with specifi c speech sounds an amorphous blob and a star-like shape across continents and linguistic families. and are asked which one is likely named The distributions of the associations “bouba” and which one “kiki”, speakers of with time and location suggest that many different languages consistently associate words arose independently, potentially the blob with the former word and the revealing deep connections between the star with the latter. Damián Blasi of the developments of languages. University of Zurich and colleagues have now found that a large proportion of ● Further reading Event with a high-energy photon candidate (green tower) and a high-energy b-jet candidate (green cone and towers contained therein). The 100 basic vocabulary items have strong D Blasi et al. 2016 PNAS 113 10818. photon and the jet are nearly back-to-back. Cosmic rays make more muons An antidote to carbon monoxide from high-energy quarks and gluons statistical precision in the pPb data. events (see fi gure) are enhanced by a factor LEDs for Alzheimer’s (“jet quenching”) and the suppression of At the end of 2016, CMS again collected of 20–30. This will enable many new Researchers at the Pierre Auger Observatory For the fi rst time, an antidote has been found quarkonium states (J/ψ and ϒ mesons). A hint pPb collisions, with a higher energy and studies that might provide conclusive results in Argentina have measured the longitudinal Researchers in the to carbon-monoxide poisoning. Ling Wang of a stronger suppression of ϒ(2S) mesons a larger accumulated data sample than on the formation of QGP in pPb events. and lateral distributions of ultra-high-energy US have unveiled a and Qinzi Xu of the University of Pittsburgh compared to ϒ(1S) mesons is observed in the in 2013. The experiment is thus poised to cosmic-ray air showers with primary energies non-invasive, drug- in Pennsylvania and collaborators gave mice 2013 pPb data, but a conclusive comparison relaunch its comprehensive search for QPG ● Further reading of 6–16 EeV (corresponding to centre-of-mass free approach to air containing 3% carbon monoxide for with PbPb data at similar high multiplicities signatures in high multiplicity pPb systems. CMS Collaboration 2013 Phys. Lett. B 718 795. energies of 110–170 TeV). The average shower treating Alzheimer’s 4.5 minutes, which would kill most humans. has not been possible because of limited Compared to 2013, the yields of relevant CMS Collaboration 2014 JHEP 04 103. is 1.33±0.16 and 1.61±0.21 times larger than disease, based on The mice recovered when given a modifi ed predicted from the leading LHC-tuned fl ickering LEDs. neuroglobin (a protein found in the brain aCCELEratOr t E C h n O L O G Y models EPOS-LHC and QGSJetII-04, Hannah Iaccarino of and retina that protects cells by binding with respectively, corresponding to an excess MIT and colleagues oxygen and nitric oxide) that was engineered Electron gun shrunk to matchbox size of muons. This suggests either fl aws in the showed that levels to bind to carbon monoxide 500 times more underlying models or a more fundamental of beta-amyloid tightly than it binds to hemoglobin. The US change in physics at these energies. plaque of the type Food and Drug Administration has promised An interdisciplinary team of researchers A UV pulse (blue) back-illuminates the gun associated with an expedited review of the work. from DESY in Germany and MIT in photocathode, producing a high-density ● Further reading Alzheimer’s in the US has built a new kind of electron electron bunch inside the gun that is A Aab et al. 2016 Phys. Rev. Lett. 117 192001. mice are reduced ● Further reading gun that is about the size of a matchbox. immediately accelerated by ultra-intense by exposure to The brain of a mouse I Azarov et al. 2016 Sci. Transl. Med. 8 368ra173. The new device uses laser-generated single-cycle terahertz pulses to energies Statistical mechanics of fl ickering LED light after seven days of terahertz radiation, rather than traditional approaching 1 keV. at frequencies one-hour per day in the Flying to reduce jet lag radio-frequency fi elds, to accelerate consciousness of 40 Hz. This dark (top) or exposure

electrons from rest. Since terahertz W Ronny Huang/CFEL/DESY/MIT Science in Hamburg. The electron beams Ramon Guevara Erra of the Université Paris corresponds to the to a 40 Hz fl icker Joseph Bass of Northwestern University radiation has a much shorter wavelength emerging from the device could already be Descartes and colleagues have reported a gamma-frequency (bottom), showing in Chicago and colleagues have made the than radio waves, the new device measures used for low-energy electron diffraction new insight into the nature of consciousness. range of brainwaves plaques (white arrows). surprising fi nding that fl ying can sometimes just 34 × 2 4. 5 × 16.8 mm – compared experiments, he says, and will also have The researchers recorded the brain activity (25–80 Hz), which The scale bar is 50 μm. reduce jet lag. After observing daily cycles in with the size of a car for traditional applications in ultrafast electron diffraction of people while they were sleeping, awake, in normal brain blood and tissue oxygen levels in mice kept on state-of-the-art electron guns. or for injecting electrons into linacs and and having epileptic seizures. They found function is associated with attention, perception a normal light–dark cycle, the team found that This device reached an accelerating X-ray light sources. that normal wakeful states are characterised and memory. One hour of exposure to the light if the mice were subjected to a six-hour-long gradient of 350 MV per metre, which the from rest to 0.5 keV with minimal energy by the greatest number of interactions reduced beta-amyloid plaque by an impressive change in light cycle that corresponded team says is almost twice that of current spread,” explains lead author W Ronny ● Further reading between brain networks, equating to the 40–50%. Levels of abnormally modifi ed Tau to fl ying east on a jet, those kept in a low electron guns. “We achieved an acceleration Huang of MIT, who carried out the work W R Huang et al. 2016 Optica DOI:10.1364/ highest entropy values. This means there is protein, also associated with Alzheimer’s concentration of oxygen adapted more of a dense packet of 250,000 electrons at the Center for Free-Electron Laser OPTICA.3.001209. higher information content in the networks disease, were also reduced. Other frequencies quickly. The mechanism involves changing associated with conscious states and suggests between 20 and 80 Hz were ineffective. Clinical the amount of HIF1α, which is required for Les physiciens des particules du monde entier sont invités à apporter leurs CERN Courier welcomes contributions from the international that consciousness could be the result of trials with humans are now being planned. oxygen levels to entrain the circadian clock. contributions au CERN Courier, en français ou en anglais. Les articles retenus particle-physics community. These can be written in English or French, optimising information processing. 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 ● Further reading ● Further reading ● Further reading H Iaccarino et al. 2016 Nature 540 230. C Peek et al. 2016 Cell Metabolism DOI:10.1016/j. faites part de vos suggestions à la rédaction à l’adresse [email protected]. an article, please send proposals to the editor at [email protected]. R Guevarra Eva et al. 2016 Phys. Rev. E 94 052402. cmet.2016.09.010.

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C OMPILED BY M ARC TÜRLER , ISDC AND O BSERVATORY OF THE U NIVERSITY OF G ENEVA , AND CHIPP, U NIVERSITY OF Z URICH Compact star hints at vacuum polarisation

By studying an isolated neutron star, Artist’s polarisation, which they say is likely due astronomers may have found the fi rst illustration to vacuum birefringence occurring in the observational indication of a strange of an isolated empty space surrounding RX J1856.5-3754. quantum effect called vacuum birefringence, neutron star They claim that such a level of polarisation which was predicted in the 1930s by Werner with an is not easily explained by other sources. Heisenberg and Hans Heinrich Euler. extreme For example, the contribution from dust

Neutron stars are the very dense remnant Reed/PennC State University magnetic grains in the interstellar medium were cores of massive stars – at least 10 times more fi eld able to estimated to be less than 1%, which was massive than our Sun – that have exploded polarise corroborated by the detection of almost as supernovae at the ends of their lives. In empty space zero polarisation in the light from 42 nearby the 1990s, the Germany-led ROSAT space and light stars. The genuine thermal radiation of the mission for soft X-ray astronomy discovered passing neutron star is also expected to be polarised a new class of seven neutron stars that are through it. by its surface magnetic fi eld, but this effect known as the Magnifi cent Seven. The should cancel out if the emission comes from faint isolated objects emit pulses of X-rays located only around 400 light-years from the entire surface of the neutron star over every three to 11 seconds or so, but unlike Earth, its extreme dimness is at the limit of which the magnetic-fi eld direction changes most pulsars they have no detectable radio the VLT’s current capabilities to measure substantially. emission. The ultra-dense stars have an polarisation. The aim of the measurement The polarisation measurement in this extremely high dipolar magnetic fi eld (of was to detect a quantum effect predicted neutron star constitutes the very fi rst the order 109–1010 T) and display an almost 80 years ago: since the vacuum is full of observational support for the predictions perfect black-body emission, making them virtual particles that appear and vanish, a of QED vacuum polarisation effects. unique laboratories to study neutron-star very strong magnetic fi eld could polarise ESO’s future European Extremely Large cooling processes. empty space and hence also light passing Telescope will allow astronomers to study A team led by Roberto Mignani from through it. Vacuum birefringence is too weak this effect around many more neutron stars, INAF Milan in Italy and the University of to be observed in laboratory experiments, but while the advent of X-ray polarimetric Zielona Gora, Poland, used ESO’s Very the phenomenon should be visible in the very space missions offers another perspective to Large Telescope (VLT) at the Paranal strong magnetic fi elds around neutron stars. this new fi eld of research. Observatory in Chile to observe the neutron After careful analysis of the VLT data, star RX J1856.5-3754. Despite being the Mignani and collaborators detected ● Further reading brightest of the Magnifi cent Seven and a signifi cant degree (16%) of linear R Mignani 2016 MNRAS 465 492.

Picture of the month

This beautiful image displays IC 405, known as the Flaming Star Nebula, in the constellation of Auriga some 1500 light-years away. Many hundreds of stars are visible in the extremely sharp view, which was taken at the 2800 m-high Mount Lemmon Sky Center Observatory in Arizona, US. The bright star visible left of centre is AE Aurigae, which was not born in this nebula but most likely in the famous Orion Nebula, from where it was ejected in a multiple star interaction. Over millions of years, the runaway star has A Block/Mount Lemmon Sky Center/University of Arizona already covered 40° on the sky relative to its birthplace. The intense ultraviolet emission of the high-speed star ionises hydrogen atoms, which then recombine and emit the characteristic reddish glow of such nebulae. Dusty fi laments are seen in blue because they refl ect the blue and ultraviolet stellar light. AE Aurigae, which is at the limit of what can be seen by the naked eye, will continue its run around the sky for some time, before exploding as a supernova.

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Gravitational-wave astronomy Gravitational-wave astronomy The dawn of a new era

From the extreme dynamics of black holes to the beginning of the universe itself, the detection of gravitational waves has opened a profound new vista on nature.

One of the greatest scientifi c discoveries of the century took place on 14 September 2015. At 09.50 UTC on that day, a train of gravitational waves launched by two colliding black holes 1.4 billion light-years away passed by the Advanced Laser Interferometer Gravitational- wave Observatory (aLIGO) in Louisiana, US, causing a fractional variation in the distance between the mirrors of about one part in 1021. Just 7 ms later, the same event – dubbed GW150914 – was picked up by the twin aLIGO detector in Washington 3000 km away (fi gure 1, overleaf). A second black-hole coalescence was observed on 26 December 2015 (GW151226) and a third candidate event was also recorded, although its statistical signifi cance was not high enough to claim a detection. A search that had gone on for half a century had fi nally met with success, ushering in the new era of gravitational-wave astronomy. Black holes are the simplest physical objects in the universe: they are made purely from war ped space and time and are fully described by their mass and intrinsic rotation, or spin. The gravitational-wave train emitted by coalescing binary black holes comprises three main stages: a long “inspiral” phase, where gravitational waves slowly and steadily drain the energy and angular momentum from the orbiting black-hole pair; the “plunge and merger”, where black holes move at almost the speed of light and then coalesce into the newly formed black hole; and the “ringdown” stage during which the remnant black hole settles to a stationary confi guration (fi gure 2, overleaf). Each dynamical stage contains fi ngerprints of the astrophysical source, which can be identifi ed by fi rst tracking the phase and amplitude of the gravitational-wave train and then by comparing it with highly accurate predictions from general relativity. aLIGO employs waveform models built by combining analyti- cal and numerical relativity. The long, early inspiral phase, char- acterised by a weak gravitational fi eld and low velocities, is well described by the post-Newtonian formalism (which expands the

An artist’s impression of the gravitational-wave universe inspired ▲ by the aLIGO discovery. (Image credit: Penelope Rose Cowley.)

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116 GW150914 . 1.0

arXiv:1410.7832 GW151226 6 103 post-Newtonian theory 041015 0.5 GW151226 + GW150914 Phys. Lett Rev. 0 2 0

/GM 10 10 2 effective one-body theory r c –0.5 ˆ L1 × (–1) | δϕ H1, shifted left by 7.3 msec strain (@ 100 HZ, whitened) –1.0 best-fit waveform, projected on L1 1 numerical relativity best-fit waveform, projected on H1 10 perturbation theory unfiltered H1 waveform –1.5 gravitational self-force

0.20 0.25 0.30 0.35 0.40 0.45 –1 0 10 seconds 10

100 101 102 103 104 105 Fig. 1. The gravitational-wave event GW150914 observed by m /m aLIGO’s Livingston (green) and Hanford (red) detectors, also 1 2 0PN 0.5PN1PN 1.5PN 2PN 2.5PN3PN 3.5PN PN order showing best-fi t templates computed by combining analytical Fig. 3. Current range of validity of the main analytical and and numerical relativity. Data for H1 are shifted by about 7 ms numerical methods to solve the two-body problem. The horizontal Fig. 4. The 90%-credible upper bounds on deviations in the to account for the time of travel between the detectors. axis shows the binary mass ratio, while the vertical axis shows the post-Newtonian coeffi cients from GW150914 and GW151226, radial separation between the two black holes in the binary. and the joint upper bounds from the two detections. Einstein fi eld equation and the gravitational radiation in pow- ers of v/c, but loses accuracy as the two bodies come closer and square degrees. This can be compared with the 0.2 square degrees extract the mass and spin of the fi nal black hole from the data. But closer). Numerical relativity provides the most accurate solution covered by the full Moon as seen from the Earth, and makes it very we expect that future, multiple gravitational-wave detections with for the last stages of inspiral, plunge, merger and ringdown, but hard to search for an electromagnetic counterpart to black-hole higher signal-to-noise ratios will shed light on these impor tant the- such models are time-consuming to produce – the state-of-the-art mergers. Nevertheless, the aLIGO results kicked off the fi rst cam- oretical questions. Despite those limitations, aLIGO has provided code of the Simulating eXtreme Spacetimes collaboration took paign for possible electromagnetic counterparts of gravitational- the most convincing evidence to date that stellar-mass compact three weeks and 20,000 CPU hours to compute the gravitational wave signals, involving almost 20 astronomical facilities spanning objects in our universe with masses larger than roughly fi ve solar waveform for the event GW150914 and three months and 70,000 the gamma-ray, X-ray, optical, infrared and radio regions of the masses are described by black holes: that is, by the solutions to the CPU hours for GW151226. spectrum. No convincing evidence of electromagnetic signals Einstein fi eld equations (see p21). A few hundred thousand different waveforms were used as tem- Fig. 2. Numerical simulations of the binary black-hole emitted by GW150914 and GW151226 was found, in line with plates by aLIGO during the fi rst observing run, covering compact coalescence of the gravitational-wave event GW150914. expectations from standard astrophysical scenarios. Deviations From binaries to cosmology binaries with total masses 2–100 times that of the Sun and mass from the standard scenario may arise if one considers dark electro- During its fi rst observation run, lasting from mid-September ratios up to 1:99. Novel approaches to the two-body problem that least one of the black holes in GW151226 was rotating at 20% of its magnetic sectors, spinning black holes with strong magnetic fi elds 2015 to mid-January 2016, aLIGO did not detect gravitational extend post-Newtonian theory into the strong-fi eld regime and maximal value or faster. Finally, the aLIGO data show that the bina- that need to be sustained until merger, and black holes surrounded waves from binaries composed of either two neutron stars, or a combine it with numerical relativity had to be developed to provide ries that produced GW150914 and GW151226 were at comparable by clouds of axions (see p45). black hole and a neutron star. Nevertheless, it set the most strin- aLIGO with accurate and effi cient waveform models, which were distances from the Earth and that the peak of the gravitational-wave aLIGO’s observations allow us to test general relativity in gent upper limits on the rates of such processes: 12.6 × 103 and based on several decades of steady work in general relativity (fi g- luminosity was about 3 × 1056 erg/sec, making them by far the most the so-far-unexplored, highly dynamical and strong-fi eld grav- 3.6 × 103 per Gpc3 per year, respectively. The aLIGO rates imply ure 3). Further theoretical work will be needed to deal with more luminous transient events in the universe. ity regime. As the two black holes that emitted GW150914 and that we expect to detect those binary systems a few years after sensitive searches in the future if we want to take full advantage of Owing to the signal’s length and the particular orientation of the GW151226 started to merge, the binary’s orbital period varied aLIGO and the French–Italian experiment Virgo reach their the discovery potential of gravitational-wave astronomy. binary plane with respect to the aLIGO detectors, no information considerably and the phase of the gravitational-wave signal design sensitivity. Observing gravitational waves from binaries about the spin precession of the system could be extracted. It has changed accordingly. It is possible to obtain an analytical rep- made up of matter is exciting because it allows us to infer the aLIGO’s fi rst black holes therefore not yet been possible to determine the precise astrophysi- resentation of the phase evolution in post-Newtonian theory, neutron-star equation of state and also to unveil the possible ori- The two gravitational-wave signals observed by aLIGO have dif- cal production route for these objects. Whereas the predictions for in which the coeffi cients describe a plethora of dynamical and gin of short-hard gamma-ray bursts (GRBs) – enormous bursts of ferent morphologies that reveal quite distinct binary black-hole the rate of binary black-hole mergers from astrophysical-formation radiative physical effects, and long-term timing observations of electromagnetic radiation observed in distant galaxies. sources. GW150914 is thought to be composed of two stellar black mechanisms traditionally vary by several orders of magnitude, the binary pulsars have placed precise bounds on the leading-order Neutron stars are extremely dense objects that form when massive

holes with masses 36 MSun and 29 MSun, which formed a black hole of aLIGO detections so far have already established the rate to be some- post-Newtonian coeffi cients. However, the new aLIGO observa- stars run out of nuclear fuel and

about 62 MSun rotating at almost 70% of its maximal rotation speed, what on the high side of the range predicted by astrophysical models tions have put the most stringent limits on higher post-Newtonian collapse. The density in the core 3 14 while GW151226 had lower black-hole masses (of about 14 MSun and at 9–240 per Gpc per year. Larger black-hole masses and higher terms – setting upper bounds as low as 10% for some coeffi cients Gravitational waves is expected to be more than 10 8 M Sun) and merged in a 21 MSun black-hole remnant. Although the coalescence rates raise the interesting possibility that a stochastic (fi gure 4). It was even possible to investigate potential deviations times the density of the Sun, at binary’s individual masses for GW151226 have larger uncertainties background of gravitational waves composed of unresolved signals during the non-perturbative coalescence phase, and again general provide us with a which the standard structure of compared with GW150914 (since the former happened at a higher from binary black-hole mergers could be observed when aLIGO relativity passed this test without doubt. pristine snapshot of nuclear matter breaks down and frequency where aLIGO sensitivity degrades), the analysis ruled reaches its design sensitivity in 2019. The fi rst aLIGO observations could neither test the second law new phases of matter such as out the possibility that the lower-mass object in GW151226 was a The sky localisation of GW150914 and GW151226, which is of black-hole mechanics, which states that the black-hole entropy the source. superfl uidity and superconduc- neutron star. A follow-up analysis also revealed that the individual mainly determined by recording the time delays of the signals cannot decrease, nor the “no-hair” theorem, which says that a black tivity may appear. All mass and ▲ black holes had spins less than 70% of the maximal value, and that at arriving at the interferometers, extended over several hundred hole is only described by mass and spin, for which we require to spin parameters being equal,

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the gravitational-wave train emitted by a binary containing a neu- Furthermore, pulsar signals offer an alternative Pulsar Timing tron star differs from the one emitted by two black holes only in the Array (PTA) detection scheme that is currently operating. Gravita- late inspiral phase, when the neutron star is tidally deformed or dis- tional waves passing through pulsars and the Earth would modify the General relativity at 100 r upted. By tracking the gravitational-wave phase it will be possible to time of arrival of the pulses, and searches for correlated signatures measure the tidal deformability parameter, which contains informa- in the pulses’ times of arrival from the most stable known pulsars by tion about the neutron-star interior, and ultimately to discriminate PTA projects could detect the stochastic gravitational-wave back- between some equations of state. The merger of double neutron stars ground from unresolved supermassive binary black-hole inspirals in and/or black-hole–neutron-star binaries is currently considered the the 10−9–10−7 Hz frequency region. Results from the North-Ameri- most likely source of short-hard GRBs, and we expect a plethora can NANOGrav, European EPTA and Australian PPTA collabora- Einstein’s masterpiece has passed every test thrown at it, most recently with of electromagnetic signals from the coalescence of such compact tions have already set interesting upper limits on the astrophysical objects that will test the short-hard GRB/binary-merger paradigm. background, and could achieve a detection in the next fi ve years. the discovery of gravitational waves, but it is vital that we Bursts of gravitational waves lasting for tenths of millisec- The past year has been a milestone for gravitational-wave research onds are also produced during the catastrophic fi nal moments of in space, with the results of the LISA Pathfi nder mission published in submit our century-old theory of gravity to further precision experiments. all stars, when the stellar core undergoes a sudden collapse (or June 2016 exceeding all expectations and proving that LISA, planned supernova explosion) to a neutron star or a black hole. At design for 2034, will work successfully (see p34). LISA would be sensitive sensitivity, aLIGO and Virgo could detect bursts from the core’s to gravitational waves between 10−4–10−2 Hz, thus detecting sources Einstein’s long path towards general relativity (GR) began in 1907, free fall and universality of gravitational redshift. Many of these “bounce”, provided that the supernova took place in the Milky different from the ones observed on the Earth such as supermassive just two years after he created special relativity (SR), when the fol- have been verifi ed to high accuracy. For instance, the universal- Way or neighbouring galaxies, with more extreme emission sce- binary black holes, extreme mass-ratio inspirals, and the astrophysi- lowing apparently trivial idea occurred to him: “If a person falls ity of the acceleration of free fall has been verifi ed on Earth at the narios observable to much further distances. Highly magnetised cal stochastic background from white-dwarf binaries in our galaxy. freely, he will not feel his own weight.” Although it was long known 10 –13 level, while the local isotropy of space has been verifi ed at rotating neutron stars called pulsars are also promising astro- In the meantime, a new ground facility to be built in 10–15 years – that all bodies fall in the same way in a gravitational fi eld, Ein- the 10 –22 level. Einstein’s fi eld equations (see panel overleaf) also physical sources of gravitational waves. Mountains just a few such as the Einstein Telescope in Europe and the Cosmic Explorer stein raised this thought to the level of a postulate: the equivalence predict many specifi c deviations from Newtonian gravity that can centimetres in height on the crust of pulsars can cause the varia- in the US – will be required to maximise the scientifi c potential principle, which states that there is complete physical equivalence be tested in the weak-fi eld, quasi-stationary regime appropriate to tion in time of the pulsar’s quadr upole moment, producing a con- of gravitational-wave physics and astrophysics. These future detec- between a homogeneous gravitational fi eld and an accelerated experiments performed in the solar system. Two of these tests – tinuous gravitational-wave train at twice the rotation frequency tors will allow such high sensitivity to binary coalescences that we reference frame. After eight Mercury’s perihelion advance, of the pulsar. The most recent LIGO all-sky searches and targeted can probe binary black holes in all our universe, enabling the most years of hard work and deep and light defl ection by the Sun observations of known pulsars have already started to invade exquisite tests of general relativity in the highly dynamical, strong- thinking, in November 1915 he – were successfully performed, the parameter space of astrophysical interest, setting new upper fi eld regime. That will challenge our current knowledge of gravity, succeeded in extracting from although with limited precision, limits on the source’s ellipticity, which depends on the neutron- fundamental and nuclear physics, unveiling the nature of the most this postulate a revolutionary soon after the discovery of GR. star’s equation of state. extreme objects in our universe. theory of space, time and grav- Since then, many high-precision Lastly, several physical mechanisms in the early universe could ity. In GR, our best description tests of such post-Newtonian have produced gravitational waves, such as cosmic infl ation, fi rst- ● Further reading of gravity, space–time ceases to gravity have been performed order phase transitions and vibrations of fundamental and/or cosmic M Armano et al. 2016 Phys. Rev. Lett. 116 231101. be an absolute, non-dynamical in the solar system, and GR strings. Being that gravitational waves are almost unaffected by mat- LIGO Scientifi c and Virgo Collaborations 2016 Phys. Rev. Lett. 116 061102. framework as envisaged by the has passed each of them with ter, they provide us with a pristine snapshot of the source at the time LIGO Scientifi c and Virgo Collaborations 2016 Phys. Rev. Lett. 116 241103. Newtonian view, and instead fl y i n g c o l o u r s . they were produced. Thus, gravitational waves may unveil a period in LIGO Scientifi c and Virgo Collaborations 2016 Phys. Rev. Lett. 116 221101. becomes a dynamical structure the history of the universe around its birth that we cannot otherwise LIGO Scientifi c and Virgo Collaborations 2016 Phys. Rev. X 6 041015. that is deformed by the presence Precision tests access. The fi rst observation run of aLIGO has set the most stringent LIGO Scientifi c and Virgo Collaborations 2016 Living Rev. Relat. 19 1. of mass-energy. Similar to what is done in preci- constraints on the stochastic gravitational-wave background, which GR has led to profound new sion electroweak experiments, it is generally expressed by the dimensionless energy density of gravi- Résumé predictions and insights that is useful to quantify the signifi - tational waves, of < 1.7 × 10−7. Digging deeper, at design sensitivity Le début d’une ère nouvelle underpin modern astrophysics cance of precision gravitational aLIGO is expected to reach a value of 10 −9, while next-generation and cosmology, and which also experiments by parameterising detectors such as the Einstein Telescope and the Cosmic Explorer L’une des plus grandes découvertes scientifi ques de notre play a central role in attempts to plausible deviations from GR. may achieve values as low as 10−13 – just two orders of magnitude siècle a eu lieu le 14 septembre 2015, lorsqu’un train d’ondes unify gravity with other inter- Gravity warps space and time. (Image credit: Isaïe Correia.) The simplest, and most conserv- above the background predicted by the standard “slow-roll” infl a- gravitationnelles issu de la collision de deux trous noirs, à 1,4 actions. By contrast to GR, our ative, deviation from Einstein’s tionary scenario. milliard d’années-lumière de la Terre, est passé à travers l’expérience current description of the fundamental constituents of matter and pure spin-2 theory is defi ned by adding a long-range (massless) aLIGO. Cet événement a marqué la fi n d’une quête qui avait duré of their non-gravitational interactions – the Standard Model (SM) spin-0 fi eld,φ , coupled to the trace of the energy-momentum tensor. Grand view un demi-siècle, et l’entrée dans la nouvelle ère de l’astronomie – is given by a quantum theory of interacting particles of spins 0, The most general such theory respecting the universality of gravi- The sensitivity of existing interferometer experiments on Earth will des ondes gravitationnelles. La capacité que nous avons à présent ½ and 1 that evolve within the fi xed, non-dynamical Minkowski tational coupling contains an arbitrary function of the scalar fi eld be improved in the next 5–10 years by employing a quantum-optics d’observer l’Univers à l’aide des ondes gravitationnelles remettra en space–time of SR. The contrast between the homogeneous, rigid defi ning the “observable metric” to which the SM matter is mini- phenomenon called squeezed light. This will reduce the sky-local- question notre connaissance actuelle de la gravité et de la physique and matter-independent space–time of SR and the inhomogene- mally and universally coupled. isation errors of coalescing binaries, provide a better measurement fondamentale, car elle pourrait dévoiler la nature des objets les ous, matter-deformed space–time of GR is illustrated in fi gure 1 In the weak-fi eld slow-motion limit, appropriate to describ- of tidal effects and the neutron-star equation of state in binary merg- plus extrêmes que nous connaissons et peut-être faire la lumière sur (overleaf). ing gravitational experiments in the solar system, the addition ers, and enhance our chances of observing gravitational waves from l’origine de l’Univers lui-même. Et ce n’est là qu’un début. The universality of the coupling of gravity to matter (which is the of φ modifi es Einstein’s predictions only through the appear- – pulsars and supernovae. The ability to identify the source of gravi- most general form of the equivalence principle) has many observ- ance of two dimensionless parameters, –γ and β. The best cur- tational waves will also improve over time, as upgraded and new Alessandra Buonanno, Max Planck Institute for Gravitational Physics, able consequences such as: constancy of the physical constants; rent limits on these “post-Einstein” parameters are, respectively, ▲ gravitational-wave observatories come online. Germany, and University of Maryland, US. local isotropy of space; local Lorentz invariance; universality of (2.1±2.3) × 10 –5 (deduced from the additional Doppler shift

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There are two equivalent ways of characterising general relativity (GR). One describes gravity as a universal deformation of the Minkowski metric, which defi nes a local squared interval between two infi nitesimally close space– time points and, consequently, the infi nitesimal light cones describing the

local propagation of massless particles. The metric fi eld gμν is assumed in GR to be universally and minimally coupled to all the particles of the Standard Model (SM), and to satisfy Einstein’s fi eld equations: Fig. 1. The non-dynamical Minkowski space–time of SR (left) and 1 8πG its regular array of light cones compared to the dynamical, R – R g = T • μν 2 μν c4 μν matter-deformed space–time of GR and its fi eld of local light In addition, several authors – including Einstein himself – had voiced r = 0 singularity Here, R denotes the Ricci curvature (a nonlinear combination of g and of μν μν cones (right). GR has been submitted, with striking success, to doubts about the existence of GWs in fully nonlinear GR. r = 2M its fi rst and second derivatives), Tμν is the stress-energy tensor of the SM many high-precision experimental tests. The situation changed in the early 1960s when Joseph Weber horizon particles (and fi elds), and G denotes Newton’s gravitational constant. understood that GWs arriving on Earth would have observ- The second way of defi ning GR, as proven by Richard Feynman, PSR B1913+16 PSR B1534+12 able effects and developed sensitive resonant detectors (“Weber . . . . Steven Weinberg, Stanley Deser and others, states that it is the unique, 2.5 P 2.5 P bars”) to search for them. Then, prompted by Weber’s experi- consistent, local, special-relativistic theory of a massless spin-2 fi eld. It mental effort, Freeman Dyson realised that, when applying the 2.0 2.0 flash of is then found that the couplings1 of the spin-28πG fi eld to the SM matter are s time R – R g = T • quadupolar energy-loss formula derived by Einstein to binary light emitted μν 2 μν c4 μν necessarily equivalent to a universal coupling to a “deformed” space–time 1.5 1.5 systems made of neutron stars, “the loss of energy by gravita- from centre 16πG 2 s ≤ 1 r metric, and that theᮀ propagationhμν – ∂μHν and– ∂ν self-couplingsHμ = – 4 T μνof ,the spin-2 fi eld are m c 1.0 1.0 tional radiation will bring the two stars closer with ever-increas- necessarily 1described by8π GEinstein’s equations. ing speed, until in the last second of their lives they plunge space Rμν – 2 R gμν = 4 Tμν • Following the examplec of Maxwell, who had found that the 0.5 0.5 together and release a gravitational fl ash at a frequency of about collapsing star electromagnetic-fi eld equations admit propagating waves as solutions, 0.0 0.0 200 cycles and of unimaginable intensity.” The vision of Dyson Einstein found that the GR fi eld equations admit propagating gravitational 0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5 has recently been realised thanks, on the one hand, to the experi- m1 m1 waves (GWs). He did so by considering the weak-fi eld limit (gμν = η μν + hμν) mental development of drastically more sensitive non-resonant PSR J1141–6545 PSR J0737–3039 of his equations, namely, kilometre-scale interferometric detectors and, on the other hand, Fig. 3. (Top) Simulation of a black-hole merger based on . x /x 16πG 2.5 . 2.5 . P SO B A to theoretical advances that allowed one to predict in advance the numerical GR. (Bottom) The gravitational collapse of a star ᮀhμν – ∂μHν – ∂νHμ = – Tμν, . P c4 accurate shape of the GW signals emitted by coalescing systems leading to the formation of a BH horizon, a hypersurface in – 2.0 2.0 s where hμν = hμν – ½h ημν. When choosing the co-ordinate system so as to sscint of neutron stars and black holes (BHs). space–time that is everywhere tangent to the light cone and satisfy the gravitational analogue of the Lorenz gauge condition, so that 1.5 1.5 r 2 The recent observations of the LIGO interferometers have whose 2D spatial sections approach asymptotically (in the – Hμ = ∂ν = 0 the linearised fi eld equations simplify to m 2 hμν , the diagonal 1.0 1.0 provided the fi rst detection of GWs in the wave zone. They also future) the r = 2GM/c 2-sphere of a Schwarzschild solution. inhomogeneous wave equation, which can be solved by retarded provide the fi rst direct evidence of the existence of BHs via the 0.5 potentials. 0.5 observation of their merger, followed by an abrupt shut-off of the cosmologies. Quantitative confi rmations of GR on cosmological There are two main results that derive from this wave equation: fi rst, 0.0 0.0 GW signal, in complete accord with the GR predictions. scales have also been obtained, notably through the observation of a GW is locally described by a plane wave with two transverse tensorial 0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5 BHs are perhaps the most extraordinary consequence of GR, a variety of gravitational lensing systems. m1 m1 polarisations (corresponding to the two helicity states of the massless spin-2 because of the extreme distortion of space and time that they graviton) and travelling at the velocity of light; second, a slowly moving, non Fig. 2. Illustration of the 11 tests of relativistic gravity obtained exhibit. In January 1916, Karl Schwarzschild published the fi rst Dark clouds ahead self-gravitating source predominantly emits a quadupolar GW. in the four known binary pulsar systems. Each curve (or strip) exact solution of the (vacuum) Einstein equations, supposedly In conclusion, all present experimental gravitational data (univer- in the mass plane corresponds to the interpretation, within GR, describing the gravitational fi eld of a “mass point” in GR. It took sality of free fall, post-Newtonian gravity, radiative and strong- of some observable timing parameter. The shaded regions about 50 years to fully grasp the meaning and astrophysical plau- fi eld effects in binary pulsars, GW emission by coalescing BHs and experienced by radio-wave beams connecting the Earth to the correspond to s > 1, which is theoretically excluded. sibility of these Schwarzschild BHs. Two of the key contribu- gravitational lensing) have been found to be compatible with the Cassini spacecraft when they passed near the Sun) and < 7 × 10 –5, tions that led to our current understanding of BHs came from predictions of Einstein’s theory. There are also strong constraints on from a study of the global sensitivity of planetary ephemerides to since the discovery of binary pulsars in 1974, providing direct Oppenheimer and Snyder, who in 1939 suggested that a neutron sub-millimetre modifi cations of Newtonian gravity from torsion- post-Einstein parameters. proof of the reality of gravitational radiation. Measurements of the star exceeding its maximum possible mass will undergo gravi- balance tests of the inverse square law. In the regime of radiative and/or strong gravitational fi elds, by arrival times of pulsar signals have also allowed precision tests of tational collapse and thereby form a BH, and from Kerr 25 years One might, however, wish to keep in mind the presence of two contrast, pulsars (rotating neutron stars emitting a beam of radio the quasi-stationary strong-fi eld regime of GR, since their values later, who discovered a generalisation of the Schwarzschild solu- dark clouds in our current cosmology, namely the need to assume waves) in gravitationally bound orbits have provided crucial tests may depend both on the unknown masses of the binary system and tion describing a BH endowed both with mass and spin. that most of the stress-energy tensor that has to be put on the right- of GR. In particular, measurements of the decay in the orbital on the theory of gravity used to describe the strong self-gravity of Another remarkable consequence of GR is theoretical cosmol- hand side of the GR fi eld equations to account for the current obser- period of binary pulsars have provided direct experimental con- the pulsar and its companion (fi gure 2). ogy, namely the possibility of describing the kinematics and the vations is made of yet unseen types of matter: dark matter and a fi rmation of the propagation properties of the gravitational fi eld. dynamics of the whole material universe. The fi eld of relativistic “cosmological constant”. It has been suggested that these signal a Theoretical studies of binaries in GR have shown that the fi nite The radiation revelation cosmology was ushered in by a 1917 paper by Einstein. Another breakdown of Einstein’s gravitation at large scales, although no velocity of propagation of the gravitational interaction between the Einstein realised that his fi eld equations had wave-like solutions in key contribution was the 1924 paper of Friedmann that described convincing theoretical modifi cation of GR at large distances has pulsar and its companion generates damping-like terms at order two papers in June 1916 and January 1918 (see panel left). For many general families of spatially curved, expanding or contracting yet been put forward. (v/c)5 in the equations of motion that lead to a small orbital period years, however, the emission of gravitational waves (GWs) by known homogeneous cosmological models. The Friedmann models still GWs, BHs and dynamical cosmological models have become ▲ decay. This has been observed in more than four different systems sources was viewed as being too weak to be of physical signifi cance. constitute the background models of the current, inhomogeneous essential elements of our description of the macroscopic universe.

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 General relativity Accelerate with You know what you want to detect: The recent and bright beginning of GW astronomy suggests that GR power and efficiency will be an essential tool for discovering new aspects of the universe (see p16). A century after its inception, GR has established itself As the market leader in terrestrial broadcasting, we raise the standard - X-rays as the standard theoretical description of gravity, with applications for efficiency and precision in particle acceleration. Choose from our ranging from the Global Positioning System and the dynamics of the Download AppCard - Gamma-rays wide portfolio of excellent high-power and broadband amplifiers and solar system, to the realm of galaxies and the primordial universe. benefit from the advantages of However, in addition to the “dark clouds” of dark matter and ❙ Amplifiers up to 100 kW and more for the storage ring - Neutrons energy, GR also poses some theoretical challenges. There are ❙ High-speed linear drive amplifiers for the klystron in - Particles both classical challenges (notably the formation of space-like singularities inside BHs), and quantum ones (namely the non- linear accelerators (LINAC) renormalisability of quantum gravity – see p27). It is probable that ❙ Fast-response amplifiers for stochastic cooling a full resolution of these challenges will be reached only through a ❙ Amplifiers with low additive phase noise for prebuncher cavities suitable extension of GR, and possibly through its unifi cation with Rohde & Schwarz offers a dedicated portfolio of T&M instruments and the current “spin ≤ 1” description of particle physics, as suggested power amplifier solutions for development, commissioning, optimization both by supergravity and by superstring theory. and operation of particle accelerators. It is therefore vital that we continue to submit GR to experimen- tal tests of increasing precision. The foundational stone of GR, the equivalence principle, is currently being probed in space at the 10 –15 www.rohde-schwarz.com/ad/particle-accelerators level by the MICROSCOPE satellite mission of ONERA and CNES. The observation of a deviation of the universality of free fall would SCIONIX Holland B.V. imply that Einstein’s purely geometrical description of gravity needs Tel. +31 30 6570312 to be completed by including new long-range fi elds coupled to bulk Fax. +31 30 6567563 We know how to matter. Such an experimental clue would be most valuable to indicate Email. [email protected] build your detectors the road towards a more encompassing physical theory. www.scionix.nl ● Further reading http://einsteinpapers.press.princeton.edu/papers. A Abramovici et al. 1992 Science 256 325. A Buonanno and T Damour 2000 Phys. Rev. D 62 064015. Y Choquet-Bruhat 2015 Introduction to General Relativity, Black Holes and Cosmology (Oxford: Oxford University Press). F Dyson 1963 “Gravitational Machines” in Interstellar Communication A G W Cameron ed. (New York: Benjamin Press). R P Kerr 1963 Phys. Rev. Lett. 11 237. LIGO Scientifi c and Virgo Collaborations 2016 Phys. Rev. X 6 041015. J R Oppenheimer and H Snyder 1939 Phys. Rev. 56 455. Particle Data Group 2016 Chin. Phys. C 40 100001. F Pretorius 2005 Phys. Rev. Lett. 95 121101.

Résumé La relativité générale fête ses 100 ans

Au cours des cent dernières années, la théorie de la gravité d’Einstein a donné naissance à de nouvelles prédictions et idées essentielles, qui sont à la base de l’astrophysique et de la cosmologie modernes. La plupart ont été confi rmées par l’expérience avec une précision stupéfi ante, et la détection des ondes gravitationnelles a été la cerise sur le gâteau pour la relativité générale. Mais l’horizon se charge de nuages menaçants. En plus de diffi cultés pour rendre compte de la matière noire et de l’énergie noire, la relativité générale pose des problèmes théoriques qui pourraient n’être résolus que par une extension appropriée de la théorie, et peut-être par son unifi cation ¸THx9 Amplifier avec la physique des particules, comme le suggèrent les théories de la supergravité et des supercordes.

Thibault Damour, Institut des Hautes Etudes Scientifi ques, France.

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21524.001_AcceleratorPhysics_THx9_CERNcourier-Jan17_213x282_e.indd 1 21.11.16 11:45 Uhr CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 Quantum gravity and unification Gravity’s quantum side

Theoretical physics has arrived at crossroads, with no clues so far as to what lies beyond general relativity or the Standard Model. If we are ever to break through this impasse, we need to borrow from Einstein’s epochal feats.

There is little doubt that, in spite of their overwhelm- ing success in describing phenomena over a vast range of distances, general relativity (GR) and the Standard Model (SM) of particle physics are incomplete theo- ries. Concerning the SM, the problem is often cast in terms of the remaining open issues in particle physics, such as its failure to account for the origin of the mat- Vecto_CERN Courier_193x125.indd 1 12/12/2016 09:23:06 ter–antimatter asymmetry or the nature of dark matter. But the real problem with the SM is theoretical: it is not clear whether it makes sense at all as a theory beyond perturba- tion theory, and these doubts extend to the whole framework Progress of of quantum fi eld theory (QFT) (with perturbation theory as the main tool to extract quantitative predictions). The occurrence of Theoretical and “ultraviolet” (UV) divergences in Feynman diagrams, and the need for an elaborate mathematical procedure called renormalisa- Experimental Physics tion to remove these infinities and make testable predictions order- by-order in perturbation theory, strongly point to the necessity of A slice Progress of Theoretical and Experimental Physics is a some other and more complete theory of elementary particles. through the On the GR side, we are faced with a similar dilemma. Like the root space of the fully open access, online-only journal. SM, GR works extremely well in its domain of applicability and symmetry group E10, a possible has so far passed all experimental tests with flying colours, most symmetry for quantum gravity. Each point is associated with Read our latest Special Section: recently and impressively with the direct detection of gravitational one or more independent symmetry operations – similar to the waves (see p21). Nevertheless, the need for a theory beyond Ein- fl avour SU(3) root diagram for the meson octet, but vastly more Nambu, A Foreteller of Modern Physics III stein is plainly evident from the existence of space–time singulari- complicated. There are infi nitely many such layers, and the This Special Section is based on a symposium ties such as those occurring inside black holes or at the moment of number of symmetry operations grows exponentially as one the Big Bang. Such singularities are an unavoidable consequence penetrates deeper and deeper into the E10 Lie algebra. held at the University of Chicago in memory of of Einstein’s equations, and the failure of GR to provide an answer (Image credit: T Nutma.) Professor Yoichiro Nambu. calls into question the very conceptual foundations of the theory. Unlike quantum theory, which is rooted in probability and Applying conventional particle-physics wisdom to Einstein’s uncertainty, GR is based on notions of smoothness and geom- theory by quantising small fluctuations of the metric field (cor- academic.oup.com/ptep etry and is therefore subject to classical determinism. Near a responding to gravitational waves) cannot help either, since it pro- space–time singularity, however, the description of space–time duces non-renormalisable infinities that undermine the predictive as a continuum is expected to break down. Likewise, the assump- power of perturbatively quantised GR. tion that elementary particles are point-like, a cornerstone of In the face of these problems, there is a wide consensus that the QFT and the reason for the occurrence of ultraviolet infinities outstanding problems of both the SM and GR can only be over- ▲ in the SM, is expected to fail in such extreme circumstances. come by a more complete and deeper theory: a theory of quantum

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to try to emulate Einstein’s epochal feat of creating a new theory The success of symmetry has fuelled hopes that we temperature 32 27 15 13 out of purely theoretical considerations. of universe 10 K10 K10 K10 K3 K might ultimately understand the evolution of the universe from its beginning as a symmetry-breaking Emulating Einstein cascade, where at each step more and more of the Yet, after more than 40 years of unprecedented collective intel- strong force initial symmetry is lost as the universe expands and lectual effort, different points of view have given rise to a growing electromagnetic force cools down. In this view, the unsymmetrical world that j3 j3 diversification of approaches to QG – with no convergence in sight. weak force we see around us is only the broken phase of a highly It seems that theoretical physics has arrived at crossroads, with symmetrical theory at the origin of the universe, when nature remaining tight-lipped about what comes after Einstein gravity forces, matter and space–time were unified into a j2 and the SM. There is currently no evidence whatsoever for any of single entity. However, this picture has so far been the numerous QG schemes that have been proposed – no signs of time after –43 –35 –12 –6 17 validated only up to energy scales accessible to the j1 10 s10 s10 s10 s5 × 10 s −18 low-energy supersymmetry, large extra dimensions or “stringy” Big Bang ( = now) LHC, or equivalently distances down to 10 cm. j1 j2 excitations have been seen at the LHC so far. The situation is no better for approaches that do not even attempt to make predictions or “canonical” approaches, the main unsolved problems concern graphic entanglement, as advocated by AdS/CFT aficionados? that could be tested at the LHC. the emergence of classical space–time and the Einstein fi eld There is cer tainly no lack of enticing ideas, but without a firm guid- If quantum space is made of web-like structures (spin networks), Existing approaches to QG fall roughly into two catego- equations in the semiclassical limit, and their inability to recover ing principle and the prospect of making a falsifiable prediction, as postulated by LQG-like approaches, a spin foam describes ries, refl ecting a basic schism that has developed in the com- standard QFT results such as anomalies. On the other side, a main such speculations may well end up in the nirvana of undecidable the quantum evolution of such spin networks in time. In the munity. One is based on the assumption that Einstein’s theory shortcoming is the “background dependence” of the quantisation propositions and untestable expectations. abstract description, the ambient space–time in which the spin can stand on its own feet, even when confronted with quantum procedure, for which both supergravity and string theory have to Why then consider unification? Perhaps the strongest argument in foam is “embedded” is simply not there, since all of the geometry mechanics. This would imply that QG is nothing more than the rely on perturbative expansions about some given space–time favour of unification is that the underlying principle of symmetry has resides on the spin foam. non-perturbative quantisation of Einstein’s theory and that GR, background geometry. In fact, in its presently known form, string so far guided the development of modern physics from Maxwell’s suitably treated and eventually complemented by the SM, cor- theory cannot even be formulated without reference to a specific theory to GR all the way to Yang–Mills theories and the SM (see gravity (QG) that possibly unifi es gravity with the other fundamental rectly describes the physical degrees of freedom also at the very space–time background. diagram above). It is therefore reasonable to suppose that unification interactions in nature. But how are we to approach this challenge? smallest distances. The earliest incarnation of this approach goes These fundamentally different viewpoints also offer different and symmetry may also point the way to a consistent theory of QG. back to the pioneering work of John Wheeler and Bryce DeWitt in perspectives on how to address the non-renormalisability of Ein- This point of view is reinforced by the fact that the SM, although Planck-scale physics the early 1960s, who derived a GR analogue of the Schrödinger stein’s theory, and consequently on the need (or not) for unification. only a partially unified theory, does already afford glimpses of trans- Unlike with quantum mechanics, whose development was driven equation in which the “wave function of the universe” encodes Supergravity and superstring theory try to eliminate the infinities of Planckian physics, independently of whether new physics shows up by the need to explain observed phenomena such as the existence the entire information about the universe as a quantum system. the perturbatively quantised theory, in particular by including fer- at the LHC or not. This is because the requirements of renormalis- of spectral lines in atomic physics, nature gives us very few hints of Alas, the non-renormalisable infi nities resurface in a different mionic matter in Einstein’s theory, thus providing a raison d’être for ability and vanishing gauge anomalies put very strong constraints on where to look for QG effects. One main obstacle is the sheer small- guise: the Wheeler–DeWitt equation is so ill-defined mathemati- the existence of matter in the world. They therefore automatically the particle content of the SM, which are indeed in perfect agreement ness of the Planck length, of the order 10−33 cm, which is the scale cally that no one until now has been able to make sense of it arrive at some kind of unification of gravity, space–time and matter. with what we see in detectors. There would be no more convincing at which QG effects are expected to become visible (conversely, in beyond mere heuristics. More recent variants of this approach in By contrast, canonical approaches attribute the ultraviolet infinities vindication of a theory of QG than its ability to predict the matter terms of energy, the relevant scale is 1019 GeV, which is 15 orders of the framework of loop quantum gravity (LQG), spin foams and to basic deficiencies of the perturbative treatment. However, to rec- content of the world (see panel overleaf). magnitude greater than the energy range accessible to the LHC). group fi eld theory replace the space–time metric by new vari- oncile this view with semiclassical gravity, they will have to invoke There is no hope of ever directly measuring genuine QG effects in ables (Ashtekar variables, or holonomies and fl uxes) in a renewed some mechanism – a version of Weinberg’s asymptotic safety – to In search of SUSY the laboratory: with zillions of gravitons in even the weakest burst attempt to overcome the mathematical diffi culties. save the theory from the abyss of non-renormalisability. Among the promising ideas that have emerged over the past dec- of gravitational waves, realising the gravitational analogue of the The opposite attitude is that GR is only an effective low-energy ades, arguably the most beautiful and far reaching is supersym- photoelectric effect will forever remain a dream. theory arising from a more fundamental Planck-scale theory, Conceptual challenges metry. It represents a new type of symmetry that relates bosons One can nevertheless speculate that QG might manifest itself whose basic degrees of freedom are very different from GR or Beyond the mathematical diffi culties to formulating QG, there are and fermions, thus unifying forces (mediated by vector bosons) indirectly, for instance via measurable features in the cosmic quantum fi eld theory. In this view, GR and space–time itself are a host of issues of a more conceptual nature that are shared by all with matter (quarks and leptons), and which endows space–time microwave background, or cumulative effects originating from assumed to be emergent, much like macroscopic physics emerges approaches. Perhaps the most important concerns the very ground with extra fermionic dimensions. Supersymmetry is very natural a more granular or “foamy” space–time. Alternatively, perhaps from the quantum world of atoms and molecules. The perceived rules of quantum mechanics: even if we could properly define and from the point of view of cancelling divergences because bosons a framework will emerge that provides a compelling explanation need to replace Einstein’s theory by some other and more funda- solve the Wheeler–DeWitt equation, how are we to interpret the and fermions generally contribute with opposite signs to loop dia- for inflation, dark energy and the origin of the universe. Although mental theory, having led to the development of supersymmetry resulting wave function of the universe? After all, the latter pretends grams. This aspect means that low-energy (N = 1) supersymmetry not completely hopeless, available proposals typically do not and supergravity, is the basic hypothesis underlying superstring to describe the universe in its entirety, but in the absence of out- can stabilise the electroweak scale with regard to the Planck scale, allow one to unambiguously discriminate between very different theory (see p41). Superstring theory is the leading contender for a side classical observers, the Copenhagen interpretation of quantum thereby alleviating the so-called hierarchy problem via the cancel- approaches, for instance when contrarian schemes like string the- perturbatively fi nite theory of QG, and widely considered the most mechanics clearly becomes untenable. On a slightly less grand scale, lation of quadratic divergences. These models predict the existence ory and loop quantum gravity vie to explain features of the early promising possible pathway from QG to SM physics. This approach there are also unresolved issues related to the possible loss of infor- of a mir ror world of super par tners that differ from the SM par ticles universe. And even if evidence has spawned a hugely varied set of activities and produced many mation in connection with the Hawking evaporation of black holes. only by their opposite statistics (and their mass), but otherwise have for new effects was found in, important ideas. Most notable among these, the AdS/CFT corre- A fur ther question that any theory of QG must eventually answer identical internal quantum numbers. say, cosmic-ray physics, these spondence posits that the physics that takes place in some volume concerns the texture of space–time at the Planck scale: do there To the great disappointment of many, experimental searches at All of the important might very well admit conven- can be fully encoded in the surface bounding that volume, as for a exist “space–time atoms” or, more specifically, web-like struc- the LHC so far have found no evidence for the superpartners pre- questions remain tional explanations. hologram, and consequently that QG in the bulk should be equiva- tures like spin networks and spin foams, as claimed by LQG-like dicted by N = 1 supersymmetry. However, there is no reason to give wide open. In the search for a consistent lent to a pure quantum fi eld theory on its boundary. approaches? (see diagram on previous page) Or does the space– up on the idea of supersymmetry as such, since the refutation of theory of QG, it therefore seems Apart from numerous technical and conceptual issues, there time continuum get dissolved into a gas of strings and branes, as low-energy supersymmetry would only mean that the most simple- ▲ that we have no other choice but remain major questions for all approaches to QG. For LQG-like suggested by some variants of string theory, or emerge from holo- minded way of implementing this idea does not work. Indeed, the

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been seen, duality symmetries have turned out to be ubiquitous in Einstein on unifi cation supergravity and string theory, and they also reveal a fascinating and unsuspected link with the so-called exceptional Lie groups. It is well known that Albert Einstein spent much of the latter part of his life The LHC’s extra dimension More recently, hints of an enormous symmetry enhancement have vainly searching for unification, although disregarding the nuclear forces also appeared in a completely different place, namely the study of and certainly with no intention of reconciling quantum mechanics and GR. cosmological solutions of Einstein’s equations near a space-like Already in 1929, he published a paper on the unified theory (pictured below). singularity. This mathematical analysis has revealed tantalising In this paper, he states with wonderful and characteristic lucidity what the evidence of a truly exceptional infinite-dimensional duality sym- criteria should be of a “good” unified theory: to describe as far as possible all metry, which goes by the name of E10, and which “opens up” as one The discovery of additional space–time phenomena and their inherent links, and to do so on the basis of a minimal gets close to the cosmological (Big Bang) singularity (see image number of assumptions and logically independent basic concepts. The p27). Could it be that the near-singularity limit can tell us about the dimensions would revolutionise physics, but second of these goals (also known as the principle of Occam’s razor) refers underlying symmetries of QG in a similar way as the high-energy to “logical unity”, and goes on to say: “Roughly but truthfully, one might say: limit of gauge theories informs us about the symmetries of the SM? after 20 years of dedicated searches at particle we not only want to understand how nature works, but we are also after the One can validly argue that this huge and monstrously complex sym- colliders, we have turned up empty handed. perhaps utopian and presumptuous goal of understanding why nature is the metry knows everything about maximal supersymmetry and the way it is and not otherwise.” finite-dimensional dualities identified so far. Equally important, and unlike conventional supersymmetry, E10 may continue to make At 10.00 a.m. on 9 August 2016, physicists gathered at the Sheraton sense in the Planck regime where conventional notions of space and hotel in Chicago for the “Beyond the Standard Model” session at time are expected to break down. For this reason, duality symmetry the ICHEP conference. The mood was one of slight disappoint- could even supersede supersymmetry as a unifying principle. ment. An excess of “diphoton” events at a mass of 750 GeV reported by the LHC’s ATLAS and CMS experiments in 2015 had not Outstanding questions shown up in the 2016 data, ending a burst of activity that saw some Our summary, then, is very simple: all of the important questions 540 phenomenology papers uploaded to the arXiv preprint server in QG remain wide open, despite a great deal of effort and numer- in a period of just eight months. Among the proposed explanations An extract from Einstein’s 1929 paper in which he set out his ous promising ideas. In the light of this conclusion, the LHC will for the putative new high-mass resonance were extra space–time approach to unifi cation. (From a contribution to a continue to play a crucial role in advancing our understanding of dimensions, an idea that has been around since Theodor Kaluza commemorative publication for Aurel Stodola, Zurich, 1929.) how everything fits together, no matter what the final outcome of and Oscar Klein attempted to unify the electromagnetic and gravi- the experiments will be. This is especially true if nature chooses tational forces a century ago. not to abide by current theoretical preferences and expectations. In the modern language of string theory, extra dimensions are initial excitement about supersymmetry in the 1970s had nothing to Over the past decades, we have learnt that the SM is a most eco- required to ensure the mathematical consistency of the theory. do with the hierarchy problem, but rather because it offered a way nomical and tightly knit structure, and there is now mounting evi- They are typically thought to be very small, close to the Planck The presence of a large extra dimension could produce a clear to circumvent the so-called Coleman–Mandula no-go theorem – a dence that minor modifi cations may suffi ce for it to survive to the length (10 –35 m). In the 1990s, however, theorists trying to solve missing-energy signal in the LHC detectors, as shown here for beautiful possibility that is precisely not realised by the models cur- highest energies. To look for such subtle deviations will therefore problems with supersymmetry suggested that some of these extra an ATLAS event recorded in 2011 with a missing transverse rently being tested at the LHC. be a main task for the LHC in the years ahead. If our view of the dimensions could be as large as 10–19 m, corresponding to an energy energy of 523 GeV. In fact, the reduplication of internal quantum numbers predicted Planck scale remains unobstructed by intermediate scales, the pop- scale in the TeV range. In 1998, as proposed by Arkani-Hamed and by N = 1 supersymmetry is avoided in theories with extended ular model-builders’ strategy of adding ever more unseen particles co-workers, theories emerged with even larger extra dimensions, scale was a game changer. Scientists from experiments at the LEP, (N > 1) supersymmetry. Among all supersymmetric theories, max- and couplings may come to an end. In that case, the challenge of which predicted detectable effects in contemporary collider exper- Tevatron and HERA colliders quickly produced tailored searches imal N = 8 supergravity stands out as the most symmetric. Its sta- explaining the structure of the low-energy world from a Planck- iments. In such large extra-dimension (LED) scenarios, gravity can for signals for this new beyond-the-Standard Model (SM) physics tus with regard to perturbative fi niteness is still unclear, although scale theory of quantum gravity looms larger than ever. become stronger than we perceive in 3D due to the increased space scenario. No evidence was found in their accumulated data, setting recent work has revealed amazing and unexpected cancellations. available. In addition to showing us an entirely different view of the lower limits on the scale of extra dimensions of around 1 TeV. However, there is one very strange agreement between this theory Résumé universe, extra dimensions offer an elegant solution to the so-called By the turn of the century, a number of possible new experimental and observation, fi rst emphasised by Gell-Mann: the number of La face quantique de la gravité hierarchy problem, which arises because the Planck scale (where signatures had been identifi ed for extra-dimension searches, many spin-1/2 fermions remaining after complete breaking of supersym- gravity becomes as strong as the other three forces) is 17 orders of of which were studied in detail while assessing the physics perfor- metry is 48 = 3 × 16, equal to the number of quarks and leptons La physique théorique est à la croisée des chemins, et nul ne sait magnitude larger than the electroweak scale. mance of the LHC experiments. For the case of LEDs, where gravity (including right-handed neutrinos) in three generations (see p41). pour l’instant ce qui se trouve au-delà de la relativité générale ou Particle physicists normally ignore gravity because it is feeble is the only force that can expand in these dimensions, high-energy To go beyond the partial matching of quantum numbers achieved du Modèle standard. Il est admis que nous ne pourrons progresser compared with the other three collider experiments were just one approach. Smaller “tabletop” so far will, however, require some completely new insights, espe- qu’avec une théorie plus complète de la gravité quantique, forces. In theories where grav- scale experiments aiming to measure the strength of gravity at sub- cially concerning the emergence of chiral gauge interactions. qui unifi erait peut-être la gravité avec les autres interactions ity gets stronger at small dis- millimetre distances were also in pursuit of extra dimensions, but Then again, perhaps supersymmetry is not the end of the story. fondamentales de la nature. Or, après plus de 40 ans d’un effort The possibility of tances due to the opening of no deviation from the Newtonian law has been observed to date. In There is plenty of evidence that another type of symmetry may be intellectuel collectif sans précédent, les approches de la gravité having extra space extra dimensions, however, it addition, there were also signifi cant constraints from astrophysics equally important, namely duality symmetry. The first example quantique sont toujours plus diversifi ées et aucune convergence dimensions at the can catch up and lead to phe- processes on the possible number and size of these dimensions. of such a symmetry, electromagnetic duality, was discovered by n’est en vue. Si nous voulons sortir un jour de cette impasse, nous nomena at colliders with high Dirac in 1931. He realised that Maxwell’s equations in vacuum devrons nous inspirer des prouesses historiques d’Einstein. TeV scale was a enough rates that they can be Enter the LHC are invariant under rotations of the electric and magnetic fields game changer. measured in experiments. The Analysis strategies to search for extra dimensions have been into one another – an insight that led him to predict the existence Hermann Nicolai, Max Planck Institute for Gravitational Physics, Potsdam, possibility of having extra deployed from the beginning of high-energy LHC operations in ▲ of magnetic monopoles. While magnetic monopoles have not Germany. space dimensions at the TeV 2010, and the recent increase in the LHC’s collision energy to

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supersymmetry candidates have been observed, pushing the lower 2.3 fb–1 (13 TeV) ATLAS 103 observed mass limits beyond 1 TeV for certain particle types. CMS 5 –1 expected limit (± 1 ␴exp) 10 data: multiplicity ≥ 8 √s = 13 TeV, 3.2 fb 2.2 fb–1 at 7 TeV diphoton CMS 8 all limits at 95% CL preliminary background from data observed limit 2 γ + jet 4 Final hope 10 10 MD = 4 TeV, MBH = 5 TeV, N = 6 dijet Collider data so far have not yet given us any sign of the existence obs. limit (after damping) MD = 4 TeV, MBH = 6 TeV, N = 6 7 3 systematic uncertainty 10 MD = 4 TeV, MBH = 7 TeV, N = 6 of extra dimensions, or for that matter a sign that gravity is becom- –1 10 ATLAS √s = 8 TeV, 20.3 fb ~ MD = 4 TeV, MBH = 8 TeV, N = 6 ing strong at the TeV scale. It is possible that, even if they exist, the k = 0.05, M1 = 1.75 TeV 2 10 extra dimensions could be as small as predicted by string theory, in 6 n = 6, M = 3 TeV 1 ED S 10 which case they would not be able to solve the hierarchy problem. events (100 GeV) lower limit (TeV)

D The idea is still very much alive, however, and searches will con- M 5 events/20 GeV 10–1 1 tinue as more data are recorded at the LHC. Even excellent and attractive ideas always need confi rmation from –1 10 data, and inevitably the initial high enthusiasm for extra-dimension 4 10–2 theories may have waned somewhat in recent years. Although such 3000 4000 5000 6000 7000 confi rmation could come from the next generation of colliders, such –3 S (GeV) 3 10 T as possible higher-energy machines, there is unfortunately no guar- Fig. 3. Distributions of the total transverse energy for events antee. It could be that we have to turn to even more outlandish ideas 2 3 4 5 6 number of extra dimensions 18001600140012001000800600400200 2000 with eight high-pT objects. Observed data are shown by to progress further. points, while the solid blue lines show the main background Mγγ (GeV) Fig. 1. Recent mono-jet searches at ATLAS have pushed estimation along with the uncertainty band. The predictions ● Further reading possible extra-dimension scales to values beyond 5–7 TeV, Fig. 2. Observed event yields and background expectations as for several semiclassical black-hole signals are also shown. ATLAS results: https://twiki.cern.ch/twiki/bin/view/AtlasPublic/ depending on the number of assumed large extra a function of the diphoton invariant mass for an early ExoticsPublicResults. dimensions available for gravity to expand into. extra-dimension study at the LHC. The simulated performed since the fi rst collisions at the LHC at 7 TeV, but none CMS results: https://twiki.cern.ch/twiki/bin/view/CMSPublic/ distributions for two extra-dimension model signal have been found. If black holes are produced closer to the forma- PhysicsResultsEXO. 13 TeV has extended the search window considerably. Although no hypotheses are shown as dotted (LED) and dashed (RS) lines. tion threshold, these would be expected to decay in a much smaller I Antoniadis 1990 Phys. Lett. B 246 377. positive signal of the presence of extra dimensions has been observed fi nal-state topology, for instance into dijets. The CMS and ATLAS N Arkani-Hamed et al. 1998 Phys. Lett. B 429 263. so far, a big leap forward has been taken in excluding large portions assumed to be intrinsically strong, but the warped space between experiments have been looking for all of these fi nal states up until S Dimopoulos and G Landsberg 2001 Phys. Rev. Lett. 87 161602. of the TeV scale phase-space where extra dimensions could live. the two branes makes it appear weak on the brane where we live. the latest 13 TeV data (fi gure 3), but no signal has been observed so L Randall and R Sundrum 1999 Phys. Rev. Lett. 83 3370. A particular feature of LED-type searches is the production of The experimental signature of such scenarios is the production of far for black-hole masses up to about 9 TeV. a single very energetic “mono-object” that does not balance the so-called Kaluza–Klein (spin-2 graviton) resonances that can be Several other possible incarnations of extra-dimension theories Résumé transverse momentum carried by anything else emerging from the observed in the invariant mass spectra of difermions or dibosons. have been proposed and searched for at the LHC. So-called TeV-type La dimension supplémentaire du LHC collision (as would be required by momentum and energy conser- The most accessible spectra to the LHC experiments include the extra dimensions allow for more SM particles, for example partners vation). Examples of such objects are particle jets, very energetic diphoton and dilepton spectra, in which no new resonance signal of the heavy W and Z bosons, to enter in the bulk, and these would La physique des particules ignore généralement la gravité, car elle photons or heavy W and Z vector bosons. Such collisions only has been found, and at present the limits on putative Kaluza–Klein show up as high-mass resonances in dilepton and other invariant est très faible en comparaison des trois autres forces. Toutefois, les appear to be imbalanced, however, because the emerging jet or gravitons are about 4 TeV, depending on RS-model parameters. mass spectra. These new resonances have a spin equal to one, and théories mettant en jeu des dimensions supplémentaires de l’espace, boson is balanced by a graviton that escapes detection. Hence SM Analyses of dijet fi nal states provide even more stringent limits of hence such signatures could be more tedious to detect because they développées à la fi n des années 1990, prédisent que la gravité n’est processes such as the production of a jet plus a Z boson that decays up to 7 TeV. Further extensions of the RS model, in particular the can interfere with the SM Drell–Yan production background. Nev- pas du tout ce qu’elle semble être, et qu’elle pourrait causer des into neutrinos can mimic a graviton production signal. The absence production of top quark–antiquark resonances, offer a more sensitive ertheless, no such resonances have been discovered so far. phénomènes exotiques dans des collisionneurs, comme des trous of any excess in the mono-jet or mono-photon event channels at signature, but despite intense searches, no signal has been detected. In so-called universal extra-dimension (UED) scenarios, all noirs microscopiques. La recherche de dimensions supplémentaires the LHC has put stringent limits on LEDs (fi gure 1), with 2010 particles have states that can go into the bulk. If this scenario is a été menée dès le début de l’exploitation du LHC, en 2010. Aucun data already bypassing previous collider search limits. LEDs can Searching in the dark correct, a completely new particle spectrum of partners of the SM signal positif n’a été observé jusqu’ici, mais les expériences ATLAS also manifest themselves as a new contribution to the continuum At the start of 2000, it was realised that large or warped extra particles should show up at the LHC at high masses. Although this et CMS ont déjà éliminé de grandes parties de l’espace de phase in the invariant mass spectrum of two energetic photons (fi gure 2) dimensions could lead to a new type of signature at the LHC: looks very much like what would be expected from supersymme- à l’échelle du TeV, et les recherches se poursuivront à mesure que or fermions (dileptons or dijets). Here too, though, no signals have microscopic black holes. These can form when two colliding try, where all known SM par ticles have par tners, the Kaluza–Klein davantage de données seront enregistrées au LHC et dans les been observed, and the LHC has now excluded such contributions partons come close enough to each other, namely to within the partners would have exactly the same spin as their SM partners, futures machines. for extra-dimension scales up to several TeV. Schwarzschild radius or black-hole event horizon, and can be as whereas supersymmetry transforms bosons into fermions and vice In 1999, another extra-dimension scenario was proposed by large as a femtometre in the presence of TeV-scale extra dimen- versa. Alas, no new particles either for Kaluza–Klein partners or Albert De Roeck, CERN, and Greg Landsberg, Brown University. Randall and Sundrum (RS), sions at the LHC. Such microscopic black holes would evaporate which led to a quite different via Hawking radiation on time scales of around 10–27 s, way before phenomenology compared with they could suck up any matter, and provide an ideal opportunity to The initial high that expected from LEDs. In study quantum gravity in the laboratory. enthusiasm for its simplest form, the RS idea Black holes that are produced with a mass signifi cantly above extra-dimension contains two fundamental 3D the formation threshold are expected to evaporate in high-energy branes: one on which most if not multi-particle fi nal states leading to plenty of particle jets, leptons, theories has waned. all SM particles live, and one on photons and even Higgs particles. Searches for such energetic which gravity lives. Gravity is multi-object fi nal states in excess of the SM expectation have been

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Catching a gravitational wave

More than a billion years ago, two black holes of about 36 and 29 solar masses merged to form a black hole of 62 solar masses. The remaining mass was emitted as gravitational waves, which were detected by the aLIGO detectors (shown is the Hanford site) on 14 September 2015. The LIGO experiment has started its second induced length changes are tiny: the fi rst detected gravitational of magnitude larger than required, with the seismic noise fall- which can produce density fl uctuations of the Earth’s surface waves, from the merger of two black holes, changed the arm length ing off at higher frequencies. A powerful solution is to suspend close to the interferometer mirrors and result in a fl uctuating observation run, with further upgrades in of the aLIGO detectors by just 4 × 10 –18 m, which is approximately the mirrors as pendulums: a pendulum acts as a low-pass fi lter, gravitational force on them. While methods of monitoring and 200 times smaller than the proton radius. Achieving the fantasti- providing signifi cant reductions in motion at frequencies above subtracting this noise are being investigated, the performance of store and several other gravitational-wave cally high sensitivity required to detect this event was the culmina- the pendulum frequency. In aLIGO, a chain of four suspended Earth-based detectors is likely to always be limited at frequencies observatories planned. tion of decades of research and development. masses is used to provide a factor 107 reduction in seismic motion. below 1 Hz by this noise source. In addition, the entire suspension is attached to an advanced seis- Thermal noise associated with the thermal energy of the mir- Battling noise mic isolation system using a variety of active and passive tech- rors and their suspensions can also cause the mirrors to move, The idea of using an interferometer to detect gravitational waves niques, which further isolate noise by a factor 1000. At 10 Hz, and providing a signifi cant noise source at low-to-mid-range frequen- Gravitational waves alternatively compress and stretch space–time was fi rst concretely proposed in the 1970s and full-scale detectors in the absence of other noise sources, these systems could already cies. The magnitude of thermal noise is related to the mechani- as they propagate, exerting tidal forces on all objects in their path. began to be constructed in the mid-1990s, including GEO600 in increase the sensitivity of the detectors to roughly 10–19 m/√(Hz). cal loss of the materials: similar to a high-quality wine glass, a Detectors such as Advanced LIGO (aLIGO) search for this subtle Germany, Virgo in Italy and the LIGO project in the US. LIGO At even lower frequencies material with a low loss will ring for a long time with a pure note distor tion of space–time by measuring the relative separation of mir- consists of detectors at two sites separated by about 3000 km – (10 μHz), the daily tides stretch because most of the thermal motion is confi ned to frequencies rors at the ends of long perpendicular arms, which form a simple Hanford (in Washington state) and Livingston in Louisiana – and and shrink the Earth by the close to the resonance. For this reason, aLIGO uses fi bres fabri- Michelson interferometer with Fabry–Perot cavities in the arms: a undertook its fi rst science runs in 2002–2008. Following a major A factor-two order of 0.4 mm over 4 km. cated from fused silica – a type of very pure glass with very low beam splitter directs laser light to mirrors at the ends of the arms and upgrade, the observatory restarted in September 2015 as aLIGO improvement over Another source of low-fre- mechanical loss – for the fi nal stage of the mir ror suspension. Pio- the refl ected light is recombined to produce an interference pattern. with an initial sensitivity four times greater than its predecessor. the aLIGO design quency noise arises from mov- neered in the GEO600 detector near Hanover in Germany, the use When a gravitational wave passes through the detector, the strain it Since the detectors measure strain in space–time, the effective ing mass interacting with the of silica fi bres in place of the steel wires used in the initial LIGO exerts changes the relative lengths of the arms and causes the inter- increase in volume, or event rate, of aLIGO is a factor 43 higher. sensitivity could be detector mirrors via the New- detectors signifi cantly reduces thermal noise from suspension. ference pattern to change. A major issue facing aLIGO designers is to isolate the detectors achieved. tonian inverse square law. The Low-loss fused silica is also used for the 40 kg interferometer The arms of the aLIGO detectors are each 4 km long to help max- from various noise sources. At a frequency of around 10 Hz, the dominant source of this noise mirrors, which use multi-layered optical coatings to achieve the ▲ imise the measured length change. Even on this scale, however, the motion of the Earth’s surface or seismic noise is about 10 orders is from surface seismic waves, high refl ectivity required. For aLIGO, a new optical coating was

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√ with contributions from 14 European countries and the US. 10–23 A survey mission called LISA Pathfinder was launched on 3 December 2015 from French Guiana. It is currently located strain (1/ 1.5 million km away at the fi rst Earth–Sun Lagrange point, and “reaction chain” side –12 will take data until the end of May 2017. The aim of LISA Path- –24 10 10 ts en fi nder was to demonstrate technologies for a space-borne gravita- m ire qu re tional-wave detector based on the same measurement philosophy “main chain” F 10–13 LP 1 2 3 side as that used by ground-based detectors. The mission has clearly 10 10 10 LISA requirements /√Hz)

frequency (Hz) –2 demonstrated that we can place test masses (gold–platinum cubes s

–14 (m 10 with 46 mm sides separated by 38 cm) into free fall, such that the The design sensitivity of aLIGO, showing the dominant noise only varying force acting on them is gravity. It has also validated penultimate mass sources. a host of complementary techniques, including: operating a drag- (3rd pendulum) –15

differential acceleration spectrum 10 10–4 10–3 10–2 10–1 100 free spacecraft using cold gas thrusters; electrostatic control of frequency (Hz) free-fl oating test masses; short-arm interferometry and test-mass reaction mass LIGO Lab LIGO 0.4 mm fused charge control. When combined, these novel features allow dif- silica fibres Initial results from LISA Pathfi nder show that the technology is ferential accelerometry at the 10–15 g level, which is the sensitivity close to meeting requirements for a full gravitational-wave needed for a space-borne gravitational-wave detector. Indeed, if detector in space (Phys. Rev. Lett. 116 231101). At frequencies Pathfi nder test-mass technology were used to build a full-scale test mass above 60 mHz, its precision is only limited by the sensing noise of LISA detector, it would recover almost all of the science originally (4th pendulum) the laser measurement system, while at lower frequencies of anticipated for LISA without any further improvements. 1–60 mHz, control over the test masses is limited by the residual The success of Pathfi nder, coming hot on the heels of the detec- Left and above: aLIGO uses a chain of four suspended masses to (and decreasing) small number of gas molecules bouncing off tion of gravitational waves, is a major boost for the international provide a factor 107 reduction in seismic motion. To achieve this them. Frequencies below 1 mHz exhibit noise as a result of gravitational-wave community. It comes at an exceptional time level of shielding, each of aLIGO’s 40 kg test masses is keeping the craft’s solar panels pointing towards the Sun, most for the fi eld, with ESA currently inviting proposals for the third suspended within a 360 kg quadruple pendulum system. of which is removable. of its Cosmic Vision “large missions” programme. Developments are now needed to move from LISA Pathfi nder to LISA proper, developed comprising a stack of alternating layers of silica and LIGO detector included a thermal compensation system to reduce Advanced Virgo, giving a network of three geographically sepa- but these are now well understood and technology development titania-doped “tantala”, reducing the coating thermal noise by about thermal lensing effects in the optics, reduced electronic noise rated detectors and thus improving our ability to locate the posi- programmes are planned and under way. The timeline for this 20%. However, at the aLIGO design sensitivity (which is roughly in control circuits and fi ner polishing of the mirror substrates to tion of gravitational-wave sources on the sky. Discussions are mission leads to a launch in the early 2030s and the success of 10 times higher than the initial aLIGO set-up) thermal noise will be reduce the amount of scattered light in the detectors. also under way for an aLIGO site in India. In Japan, the KAGRA Pathfi nder means we can look forward with excitement to the the limiting noise source at frequencies of around 60 Hz – close to detector is under construction: this detector will use cryogenic fantastic science that will result. the frequency at which the detectors are most sensitive. Upgrades on the ground cooling to reduce thermal noise and is located underground to aLIGO also has much reduced quantum noise compared Having detected their fi rst gravitational wave almost as soon as reduce seismic and gravity gradient effects. When complete, Résumé with the original LIGO. This noise source has two components: they switched on in September 2015, followed by a further event a KAGRA is expected to have similar sensitivity to aLIGO. Comment attraper une onde gravitationnelle radiation-pressure noise and shot noise. The former results from few months later, the aLIGO detectors began their second obser- Longer term, in Europe a detector known as the Einstein Tel- fl uctuations in the number of photons hitting the detector mir- vation run on 30 November. Dubbed “O2”, it is scheduled to last escope (ET) has been proposed to provide a factor 10 more sensi- L’expérience aLIGO, qui a réalisé la première détection d’ondes rors, which is more signifi cant at lower frequencies, and has been for six months. More observation runs are envisaged, with more tivity than aLIGO. ET would not only have arms measuring 10 km gravitationnelles l’année passée, a entamé sa deuxième campagne reduced by using mirrors four times heavier than the initial LIGO upgrades in sensitivity taking place between them. long but would take a new approach to noise reduction using two d’observation. Des améliorations sont prévues pour le futur, et mirrors. Photon shot noise, resulting from statistical fl uctuations The next major upgrade, expected in around 2018, will see the very different detectors: a high-power room-temperature interfer- d’autres observatoires terrestres sont également en projet dans le in the number of photons at the output of the detector, limits sen- injection of “squeezed light” to further reduce quantum noise. How- ometer optimised for sensitivity at high frequencies, where shot monde. À cela s’ajoute le succès de la mission LISA, de bon augure sitivity at higher frequencies. Since shot noise is inversely pro- ever, to gain the maximum sensitivity improvement from squeezing, noise limits performance, and a low-power cryogenic interferome- pour un futur détecteur d’ondes gravitationnelles dans l’espace. portional to the square root of the power, it can be reduced by a reduction in coating thermal noise is also likely to be required. With ter optimised for sensitivity at low frequencies (where performance La sensibilité extraordinairement élevée qu’il a fallu atteindre using higher laser power. In the fi rst observing run of aLIGO, these and other relatively short-term upgrades, it is expected that a is limited by thermal noise). ET would require signifi cant changes pour détecter les infi mes déplacements causés par les ondes 100 kW of laser power was circulating in the detector arms, with factor-two improvement over the aLIGO design sensitivity could in detector technology and also be constructed underground to gravitationnelles (plus de 200 fois plus petits que le rayon d’un the potential to increase it to up to 750 kW in future runs. Opti- be achieved. This would allow events such as the fi rst detection to reduce the effect of seismic noise and gravity-gradient noise on proton) a été l’aboutissement de dizaines d’années de recherche et cal cavities are also used to store light in the arms and build up be observed with a signal-to-noise ratio almost 10 times better than low-frequency sensitivity. de développement dans la réduction du bruit et l’amélioration de laser power. the initial result. Further improvements in sensitivity will almost l’optique. In addition to reductions in these fundamental noise sources, certainly require more extensive upgrades or new facilities, possibly The fi nal frontier many other technological improvements were required to reduce involving longer detectors or cryogenic cooling of the mirrors. Obtaining signifi cantly improved sensitivity at lower frequen- Iain Martin, Christian Killow and Giles Hammond, Institute for more technical noise sources. Improvements over the initial aLIGO is expected to soon be joined in observing runs by cies is diffi cult on Earth because they are swamped by local mass Gravitational Research, University of Glasgow, UK.

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ARCA Flow Group worldwide: Competence in valves, pumps & cryogenics The AEgIS fl ight tube from which atoms of antihydrogen will be fi red to test if antimatter falls under gravity the same way matter does. Three CERN experiments are preparing to site gravitational force to matter and therefore “falls” up. Neverthe- less, precise measurements of the free fall of antiatoms could reveal measure the gravitational behaviour subtle differences that point to a crack in our current understanding.

comsol multiphysics ® of antihydrogen. Violating equivalence To date, most efforts at the AD have focused on looking for CPT

application builder violation by comparing the spectroscopy of antihydrogen to Measuring the effect of gravity on antimatter is a long-standing its well-known matter counterpart, hydrogen. Now we are in a story. It started with a project at Stanford in 1968 that attempted position to test Einstein’s equivalence principle with antimatter to measure the free fall of positrons, but a trial experiment with by directly measuring the free fall of antiatoms on Earth. The MULTIPHYSICS electrons showed that environmental effects swamped the effect of equivalence principle is the keystone of general relativity and application gravity and the fi nal experiment was not performed. In the 1990s, states that all par ticles with the same initial position and velocity the PS200 experiment at CERN’s LEAR facility attempted the should follow the same trajectories in a given gravitational fi eld. FOR EVERYONE same feat with antiprotons, but the project ended with the termina- On the other hand, quantum theories such as supersymmetry or tion of LEAR before any robust measurement could be made. To superstrings do not necessarily lead to an equivalent force on date, indirect measurements have set limits on the deviation from matter and antimatter (technically, the terms related to gravity The evolution of computational tools for standard gravity at the level of 10–6. in the Lagrangians are not bound to be the same for matter and numerical simulation of physics-based Thanks to advances in cooling and trapping technology, and antimatter). This is also the case when Lorentz-symmetry violat- systems has reached a major milestone. the construction of a new synchrotron at CERN called ELENA, ing terms are included in the Standard Model of particle physics. Custom applications are now being developed three collaborations are now preparing experiments at CERN’s Any difference seen in the behaviour of antimatter and matter by simulation specialists using the Application Antiproton Decelerator (AD) facility to measure the behaviour of with respect to gravity would mean that the equivalence princi- Builder in COMSOL Multiphysics®. antihydrogen (a positron orbiting an antiproton) under gravity. The ple is not perfect and force us to understand quantum effects in With a local installation of COMSOL Server™, applications can be ALPHA experiment has already analysed its data on the trapping the gravitational arena. Experiments performed with free-falling deployed within an entire organization and accessed worldwide. of antihydrogen atoms to set upper limits on differences in the matter atoms have so far found no difference to that of macro- free-fall rate of matter and antimatter, and is now designing a new scopic objects. Such tests have set limits at the level of one part in Make your organization truly benefit from the power of analysis. set-up. AEgIS is currently putting its apparatus through its paces, 1013, but have not yet been able to test the equivalence principle at comsol.com/application-builder while GBAR will start installation in 2017. the level where supersymmetric or other quantum effects would Given that most of the mass of antinuclei comes from massless appear. Since the amplitude of these effects could be different for ▲ © Copyright 2016 COMSOL. COMSOL, COMSOL Multiphysics, Capture the Concept, COMSOL Desktop, COMSOL Server, LiveLink, and Simulation for Everyone are either registered trademarks or trademarks of COMSOL AB. All other trademarks are the property of their respective owners, and COMSOL AB and its subsidiaries and products are not affiliated with, endorsed by, sponsored by, or supported by those trademark owners. For a list of such trademark owners, see www.comsol.com/trademarks gluons, it is extremely unlikely that antimatter experiences an oppo- antimatter, the AD experiments might have a better opportunity

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H and H+ antihydrogen atoms to interact with a beam of photons, promising a sensitivity in the 10–6 range. porous target Ps e+ porous target The many lives of Cooling matter e+ Ps double laser pulse In the case of AEgIS, the defl ectometer principle that underpins accelerating laser pulse the measurement has already been demonstrated with matter Ps* electric field atoms and with antiprotons, while the time-of-fl ight measure- p ment is straightforward in the case of GBAR. The diffi culty for supergravity p H beam the experiments lies in preparing suffi cient numbers of antiatoms p + Ps → H + e– * * – at the required low velocities. ALPHA has already demonstrated p + Ps → H + e + – H + Ps → H + e trapping of several hundred antiatoms at a temperature below The production of antihydrogen in AEgIS (left) and GBAR (right) 0.5 K, corresponding to random velocities of the order 10 m/s. The is performed via the interaction of antiprotons with positronium antiatoms are formed by letting the antiprotons traverse a plasma (Ps). In AEgIS, a plasma of antiprotons at rest in a Penning trap of positrons located within the same Penning trap. is showered with excited positronium atoms, producing excited A different scheme is used in AEgIS and GBAR to form and antihydrogen atoms that are accelerated to form a beam. In possibly cool the antiatoms and anti-ions. In AEgIS, antiprotons GBAR, a dense positronium cloud is traversed by a beam of are cooled within a Penning trap and receive a shower of positro- antiprotons to produce antihydrogen atoms and ions. nium atoms (bound e+e– pairs) to form the antiatoms. These are then slightly accelerated by electric fi elds (which act on the atoms’ to test such quantum effects. Any difference would probably not induced electric-dipole moments) so that they exit the charged change anything in the observable universe, but it would point to particle trap axially in the form of a neutral beam. For GBAR, the the necessity of having a quantum theory of gravity. antiproton beam traverses a cloud of positronium to form the anti- AEgIS plans to measure the vertical deviation of a pulsed hori- ions, which are then cooled to a few μK by forcing them to interact zontal beam of cold antihydrogen atoms, generated by bringing with laser-cooled beryllium ions. laser-excited positronium moving at several km/s into contact with In this race towards low energies, ALPHA and AEgIS are located cold antiprotons, travelling with a velocity of a few hundred m/s. on the beam at the AD, which delivers 5 MeV antiprotons. While The resulting highly excited antihydrogen atoms are then acceler- AEgIS is already commissioning its dedicated gravity experiment, ated horizontally and a moiré defl ectometer used to measure the ALPHA will move from spectroscopy to gravity in the coming vertical deviation, which is expected to be a few microns given the months. GBAR, which will be the fi rst experiment to make use of approximately 1 m-long fl ight tube of AEgIS. Reaching the lowest the beam delivered by ELENA, is now beginning installation and possible antiproton temperature minimises the divergence of the expects fi rst attempts at anti-ion production in 2018. ELENA will beam and therefore maximises the fl ux of antihydrogen atoms that decelerate antiprotons coming from the AD from 5 MeV to just Forty years after theorists married general In the early 1970s, grand unifi ed theories (GUTs), based on larger end up on the downstream detector. 100 keV, making it more effi cient to trap and store antimatter. Fol- gauge symmetries that include the SM’s “SU(3) × SU(2) × U(1)” In GBAR, which takes advantage of advances in ion-cooling lowing commissioning fi rst with protons and then with hydrogen relativity with supersymmetry, supergravity structure, did unify colour and charge – thereby uniting the strong – techniques, antihydrogen ions (H+) are produced with veloci- ions, ELENA should receive its fi rst antiprotons in the middle of and electroweak interactions. However, they relied on a huge new continues to carve out new directions in the 16 ties of the order of 0.5 m/s. In a second step, the anti-ions will be 2017 (CERN Courier December 2016 p16). Along with precision energy scale (~10 GeV), just a few orders of magnitude below the stripped of one positron to give an ultra-slow neutral antiatom that tests of CPT invariance, this facility will help to ensure that any search for a unifi ed theory. Planck scale of gravity (~1019 GeV) and far above the electroweak is allowed to enter free fall. The time of free fall over a height of differences in the gravitational antics of antimatter are not missed. Fermi scale (~10 2 GeV), and on new particles carrying both colour 20 cm is as long as 200 ms, which is easily measurable. These num- and electroweak charges. As a result, GUTs made the stunning pre- bers cor respond to the gravitational acceleration known for matter Résumé The early 1970s was a pivotal period in the history of particle phys- diction that the proton might decay at detectable rates, which was atoms, and the expected sensitivity to small deviations is 1% in the L’antimatière tombe-t-elle vers le haut ? ics. Following the discovery of asymptotic freedom and the Brout– eventually excluded by underground experiments, and their two fi rst phase of operation. Englert–Higgs mechanism a few years earlier, it was the time when widely separated cut-off scales introduced a “hierarchy problem” The ALPHA-g experiment will release antihydrogen atoms Le principe d’équivalence est au centre de la théorie de la relativité the Standard Model (SM) of electroweak and strong interactions that called for some kind of stabilisation mechanism. from a vertical magnetic atom trap and record their positions générale ; selon ce principe, testé avec une précision toujours plus came into being. After decades of empirical verifi cation, the theory A possible solution came from a parallel but unrelated devel- when they annihilate on the walls of the experiment. In a proof- fi ne au cours des dernières décennies, toute la matière tombe à received a fi nal spectacular confi rmation with the discovery of the opment. In 1973, Julius Wess and Bruno Zumino unveiled a new of-principle experiment using the original ALPHA atom trap, the la même vitesse. Trois collaborations (ALPHA, AEgIS et GBAR) Higgs boson at CERN in 2012, and its formulation has also been symmetry of 4D quantum fi eld theory: supersymmetry, which acceleration of antihydrogen atoms by gravity was constrained préparent actuellement des expériences auprès du Décélérateur recognised by Nobel prizes awarded to theoretical physics in 1979, interchanges bosons and fermions and, as would be better appreci- to lie anywhere between –110 g and 65 g. ALPHA-g improves d’antiprotons du CERN afi n de vérifi er si ce principe est valable 1999, 2004 and 2013. ated later, can also conspire to stabilise scale hierarchies. Super- on this original demonstration by orienting the trap vertically, également pour l’antimatière, en mesurant la manière dont It was clear from the start, however, that the SM, a spontaneously symmetry was inspired by “dual resonance models”, an early thereby enabling better control of the antiatom release and les atomes d’antihydrogène tombent sous l’effet de la gravité. broken gauge theory, had two major shortcomings. First, it is not version of string theory pioneered by Gabriele Veneziano and improving sensitivity to the vertical annihilation position. In the Toute différence par rapport à des atomes d’hydrogène normal a truly unifi ed theory because the gluons of the strong (colour) extended by André Neveu, Pierre Ramond and John Schwarz. Ear- new arrangement, antihydrogen gravitation can be measured at suggérerait que des effets quantiques entrent en ligne de compte ; force and the photons of electromagnetism do not emerge from a lier work done in France by Jean-Loup Gervais and Benji Sakita, the 10% level, which would already settle the question of whether nous aurions alors besoin d’une théorie quantique de la gravité. common symmetry. Second, it leaves aside gravity, the other fun- and in the Soviet Union by Yuri Golfand and Evgeny Likhtman, antimatter falls up or down, but improvements in cooling tech- damental force of nature, which is based on the gauge principle of and by Dmitry Volkov and Vladimir Akulov, had anticipated some niques will allow measurements at the 1% level. A long-term Patrice Perez, CEA-Irfu Saclay, Michael Doser, CERN, and general co-ordinate transformations and is described by general of supersymmetry’s salient features. ▲ aspiration of the ALPHA-g project is to use techniques that cause William Bertsche, University of Manchester. relativity (GR). An exact supersymmetry would require the existence of

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fi eld of supersymmetry, just like the photon is the gauge fi eld of internal circle rotations. If one or more local supersymmetries electromagnetic N helicity content electroweak 3 (whose number will be denoted by N) accompany general co- 1 [(2), ( 2 ( ] ordinate transformations, they grant the consistency of gravitino weak GUTs ? 2 3 interactions. In a subclass of “pure” supergravity models, super- [(2), 2 ( 2 ( , (1)] strong symmetry also allows one to connect “marble” and “wood” and 3 1 3 [(2), 3 ( 2 ( , 3(1), ( 2 ( ] therefore goes well beyond the KK mechanism, which does not supersymmetry? SSMs ? SUSY GUTs ? 4 [(2), 4 ( 3 ( , 6(1), 4( 1 ( , 2(0)] link Bose and Fermi fi elds. Curiously, while GR can be formulated gravitational 2 2 in any number of dimensions, seven additional spatial dimensions, 3 1 supergravity? 5 [(2), 5 ( 2 ( , 10(1), 11( 2 ( , 10(0)] at most, are allowed in supergravity due to intricacies of the Fermi– M-theory ? 3 1 Bose matching. 6 [(2), 6 ( 2 ( , 16(1), 26( 2 ( , 30(0)] Participants of the fi rst workshop on supergravity, held at Stony Last year marked the 40th anniversary of the discovery of superstrings? 3 1 8 [(2), 8 ( ( , 28(1), 56( ( , 70(0)] Brook in September 1979. (From P Van Nieuwenhuizen and supergravity. At its heart lie some of the most beautiful ideas in the- 2 2 D Freedman ed 1979 Supergravity. Proceedings, Workshop At oretical physics, and therefore over the years this theory has man- Current attempts to unify the fundamental interactions. The particles of “pure” supergravity theories in four Stony Brook, 27–29 September 1979 (North-Holland).) aged to display different facets or has lived different parallel lives. dimensions, which coincide for N = 7, 8. Here (0) indicates a discovery of reformulations where N = 1 4D supersymmetry is scalar, (1/2) a Majorana fermion, (1) a vector, (3/2) a gravitino superpartners in the SM, but it would also imply mass degenera- Construction begins manifest. This technical step was vital to simplify more general and (2) the graviton. The numbers not within brackets indicate cies between the known particles and their superpartners. This The fi rst instance of supergravity, containing a single gravitino constructions involving matter, since only this minimal form of particle multiplicities. option has been ruled out over the years by several experiments at (N = 1), was built in the spring of 1976 by Daniel Freedman, Peter supersymmetry is directly compatible with the chiral (parity-vio- CERN, Fermilab and elsewhere, and therefore supersymmetry can van Nieuwenhuizen and one of us (SF). Shortly afterwards, the result lating) interactions of the SM. Indeed, by the early 1980s, theorists fundamental consistency condition that is automatically granted be at best broken, with superpartner masses that seem to lie beyond was recovered by Stanley Deser and Bruno Zumino, in a simpler managed to construct complete couplings of supergravity to matter in the SM by its known particle content. the TeV energy region currently explored at the LHC. Moreover, and elegant way that extended the fi rst-order (“Palatini”) formal- for N = 1 and even for N = 2. Anomaly cancellation left just fi ve possible versions of string a spontaneous breaking of supersymmetry would imply the exist- ism of GR. Further simplifi cations emerged once the signifi cance of The maximal, pure N = 8 4D supergravity was also derived, theory in 10 dimensions: two “heterotic” theories of closed strings, ence of additional massless (“Goldstone”) fermions. local supersymmetry was better appreciated. Meanwhile, the “spin- via a circle KK reduction, in 1978 by Eugene Cremmer and Ber- where the SU(3) × SU(2) × U(1) symmetry of the SM is extended Supergravity, the supersymmetric extension of GR, came to the ning string” – the descendant of dual resonance models that we have nard Julia. This followed their remarkable construction, with Joel to the larger groups SO(32) or E8 × E8; an SO(32) “type-I” the- rescue in this respect. It predicted the existence of a new particle of already met – was connected to space–time supersymmetry via the Scherk, of the unique 11D form of supergravity, which displayed a ory involving both open and closed strings, akin to segments and spin 3/2 called the gravitino that would receive a mass in the bro- so-called Gliozzi–Scherk–Olive (GSO) projection, which refl ects a particularly simple structure where a single gravitino accounts for circles, respectively; and two other very different and naively ken phase. In this fashion, one or more gravitinos could be poten- subtle interplay between spin-statistics and strings in space–time. eight 4D ones. In contrast, the N = 8 model is a theory of unprec- less interesting theories called IIA and IIB. At low energies, tially very heavy, while the additional massless fermions would be The low-energy spectrum of the resulting models pointed to previ- edented complication. It was built after an inspired guess about the supergravity emerges from all of these theories in its different “eaten” – much as it occurs for part of the Higgs doublet in the SM. ously unknown 10D versions of supergravity, which would include interactions of its 70 scalar fi elds (see table) and a judicious use of 10D realisations, opening up unprecedented avenues for linking the counterparts of several gravitinos, and also to a 4D Yang–Mills generalised dualities, which extend the manifest symmetry of the 10D strings to the interactions of particle physics. Moreover, the Seeking unifi cation theory that is invariant under four distinct supersymmetries (N = 4). Maxwell equations under the interchange of electric and magnetic extended nature of strings made all of these enticing scenarios free Supergravity, especially when formulated in higher dimensions, A fi rst extended (N = 2) version of 4D supergravity involving two fi elds. The N = 8 supergravity with SO(8) gauge symmetry fore- of the ultraviolet problems of gravity. was the fi rst concrete realisation of Einstein’s dream of a unifi ed gravitinos came to light shortly after. seen by Gell-Mann was then constructed by Bernard de Wit and Following this 1984 “fi rst superstring revolution”, one might well fi eld theory (see diagram opposite). Although the unifi cation of When SF visited Caltech in the autumn of 1976, he became Hermann Nicolai. It revealed a negative vacuum energy, and thus say that supergravity offi cially started a second life as a low-energy gravity with other forces was the central theme for Einstein during aware that Murray Gell-Mann had already worked out many con- an anti-de Sitter (AdS) vacuum, and was later connected to 11D manifestation of string theory. Anomaly cancellation had somehow the last par t of his life, the beautiful equations of GR were for him a sequences of supersymmetry. In particular, Gell-Mann had real- supergravity via a sphere KK reduction. Regarding the ultraviolet connected Einstein’s “marble” and “wood” in a miraculous way source of frustration. For 30 years he was disturbed by what he con- ised that the largest “pure” 4D supergravity theory, in which all behaviour of supergravity theories, which was vigorously investi- dictated by quantum consistency, and defi nite KK scenarios soon sidered a deep fl aw: one side of the equations contained the curva- forces would be connected to the conventional graviton, would gated soon after the original discovery, no divergences were found, emerged that could recover from string theory both the SM gauge ture of space–time, which he regarded as “marble”, while the other include eight gravitinos. Moreover, this N = 8 theory could also at one loop, in the “pure” models, and many more unexpected can- group and its chiral, parity-violating interactions. Remarkably, this contained the matter energy, which he compared to “wood”. In allow an SO(8) gauge symme- cellations of divergences have since come to light. The case of N = 8 construction relied on a specifi c class of 6D internal manifolds called retrospect, Einstein wanted to turn “wood” into “marble”, but after try, the rotation group in eight supergravity is still unsettled, and some authors still expect that Calabi–Yau spaces that had been widely studied in mathematics, special and general relativity he failed in this third great endeavour. dimensions (see table oppo- this maximal theory be fi nite to all orders. thereby merging 4D supergravity with algebraic geometry. Calabi– GR has, however, proved to be an inestimable source of deep Attaining a deeper site). Although SO(8) would Yau spaces led naturally, in four dimensions, to a GUT gauge group insights for unifi cation. A close scrutiny of general co-ordinate theoretical not suffi ce to accommodate the The string revolution E6, which was known to connect to the SM with right-handed neutri- transformations led Theodor Kaluza and Oskar Klein (KK), in the understanding SU(3) × SU(2) × U(1) symmetry Following the discovery of supergravity, the GSO projection nos, also providing realisations of the see-saw mechanism. 1920s and 1930s, to link electromagnetism and its Maxwell poten- group of the SM, the full inter- opened the way to connect “spinning strings”, or string theory as tials to internal circle rotations, what we now call a U(1) gauge sym- of broken play between supergravity and they came to be known collectively, to supersymmetry. Although A third life metry. In retrospect, more general rotations could also have led to supersymmetry supersymmetric matter soon the link between strings and gravity had been foreseen by Scherk The early 1990s were marked by many investigations of black-hole- the Yang–Mills theory, which is a pillar of the SM. According to KK, in supergravity found a proper setting in string and Schwarz, and independently by Tamiaki Yoneya, it was only like solutions in supergravity, which soon unveiled new aspects of Maxwell’s theory could be a mere byproduct of gravity, provided theory, as we shall see. a decade later, in 1984, that widespread activity in this direction string theory. Just like the Maxwell fi eld is related to point particles, the universe contains one microscopic extra dimension beyond time appears crucial The following years, 1977 began. This followed Schwarz and Michael Green’s unexpected some of the fi elds in 10D supergravity are related to extended objects, and the three observable spatial ones. In this 5D picture, the photon today. and 1978, were most productive discovery that gauge and gravitational anomalies cancel in all generically dubbed “p-branes” (p = 0 for particles, p = 1 for strings, arises from a por tion of the metric tensor – the “marble” in GR – with and drew many people into the versions of 10D supersymmetric string theory. Anomalies – quan- p = 2 for membranes, and so on). String theory, being based at low one “leg” along space–time and the other along the extra dimensions. fi eld. Important developments tum violations of classical symmetries – are very troublesome energies on supergravity, therefore could not be merely a theory of ▲ Supergravity follows in this tradition: the gravitino is the gauge followed readily, including the when they concern gauge interactions, and their cancellation is a strings. Rather, as had been strongly advocated over the years by

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11D M-theory revealed a unique, if elusive, underlying principle connecting the known types of string theory, Linking waves to particles since the six theories at the edges of the diagram are all heterotic E8 x E8 type IIA equivalent. The sides of the diagram refl ect different duality links. Some were inspired by supergravity, while M-theory the others had already surfaced in the late 1980s. They are beyond its reach but fi nd their rationale in the “T-duality” heterotic SO(32) type IIB link between strings in large and small KK volumes, Gravitational waves do not just tell us about the largest objects in the universe – they may also and in the “orientifold” link proposed by one of us (AS). type I shed light on searches for dark matter, new light fi elds and other microscopic phenomena.

Michael Duff and Paul Townsend, we face a far more complicated foundations lie in the prescient 1973 work of Volkov and Akulov. soup of strings and more general p-branes. A novel ingredient was Non-linear supersymmetry arises when super par tners are exceed- a special class of p-branes, the D-branes, whose role was clarifi ed ingly massive, and seems to play an intriguing role in string theory. by Joseph Polchinski, but the electric-magnetic dualities of the low- The current lack of signals for supersymmetry at the LHC makes energy supergravity remained the key tool to analyse the system. one wonder whether it might also hold a prominent place in an The end result, in the mid 1990s, was the awesome, if still somewhat eventual picture of particle physics. This resonates with the idea vague, unifi ed picture called M-theory, which was largely due to of “split supersymmetry”, which allows for large mass splittings Edward Witten and marked the “second superstring revolution”. among superpartners and can be accommodated in supergravity Twenty years after its inception, supergravity thus started a third at the price of reconsidering hierarchy issues. parallel life, as a deep probe into the mysteries of string theory. In conclusion, attaining a deeper theoretical understanding of The late 1990s witnessed the emergence of a new duality. The broken supersymmetry in supergravity appears crucial today. In AdS/CFT correspondence, pioneered by Juan Maldacena, is a breaking supersymmetry, one is confronted with important con- profound equivalence between supergravity and strings in AdS ceptual challenges: the resulting vacua are deeply affected by quan- and conformal fi eld theory (CFT) on its boundary, which con- tum fl uctuations, and this reverberates on old conundrums related nects theories living in different dimensions. This “third super- to dark energy and the cosmological constant. There are even signs string revolution” brought to the forefront the AdS versions of that this type of investigation could shed light on the backbone of supergravity, which thus started a new life as a unique tool to string theory, and supergravity may also have something to say probe quantum fi eld theory in unusual regimes. The last two about dark matter, which might be accounted for by gravitinos or Gravitational waves could provide a link between strong gravity (left) and particle physics (right). decades have witnessed many applications of AdS/CFT outside other light superpartners. We are confi dent that supergravity will of its original realm. These have touched upon fl uid dynamics, lead us farther once more. Black holes are arguably humankind’s most intriguing intellectual The existence of black holes quark–gluon plasma, and more recently condensed-matter phys- construction. Featuring a curvature singularity where space–time The standard criterion with which to identify a black hole is ics, providing a number of useful insights on strongly coupled ● Further reading “ends” and tidal forces are infi nite, black-hole interiors cannot be straightforward: if an object is dark, massive and compact, it’s a black matter systems. Perhaps more unexpectedly, AdS/CFT duality K Becker, M Becker and J H Schwarz 2007 String Theory and M-Theory: properly understood without a quantum theory of gravity. They hole. But are there other objects which could satisfy the same crite- has stimulated work related to scattering amplitudes, which may A Modern Introduction (Cambridge University Press). are defi ned by an event horizon – a surface beyond which noth- ria? Ordinary stars are bright, while neutron stars have at most three also shed light on the old issue of the ultraviolet behaviour of S Deser and B Zumino 1976 Phys. Lett. B 62 335. ing escapes to the outside – and an exterior region called a photo- solar masses and therefore neither is able to explain observations of supergravity. The reverse programme of gaining information D Freedman, P van Nieuwenhuizen and S Ferrara 1976 Phys. Rev. D 13 3214. sphere, which is able to trap light rays. These uncommon properties very massive dark objects. In recent years, however, unknown phys- about gravity from gauge dynamics has proved harder, and it is D Freedman and A Van Proeyen 2012 Supergravity (Cambridge University Press). explain why black holes were basically ignored for half a century, ics and quantum effects in particular have been invoked that change diffi cult to foresee where the next insights will come from. Above considered little more than a bizarre mathematical solution of Ein- the structure of the horizon, replacing it by a hard surface. In this all, there is a pressing need to highlight the geometrical princi- Résumé stein’s equations but one without counterpart in nature. scenario, the exterior region – including the photosphere – would ples and the deep symmetries underlying string theory, which Les multiples vies de la supergravité LIGO’s discovery of gravitational waves provides the strongest remain unchanged, but black holes would be replaced by very com- have proved elusive over the years. evidence to date for the existence of black holes, but these tiny pact, dark stars. These stars could be made of normal matter under The interplay between particle physics and cosmology is a Quarante ans après le mariage célébré par les théoriciens entre distortions of space–time have much more to tell us. Gravitational extraordinary quantum conditions or of exotic matter such as new natural arena to explore consequences of supergravity. Recent la relativité générale et la supersymétrie, la supergravité continue waves offer a unique way to test the basic tenets of general relativ- scalar particles that may form “boson stars”. experiments probing the cosmic microwave background, and in d’ouvrir de nouvelles voies dans la quête d’une théorie unifi ée. La ity, some of which have been taken for granted without observa- Unfortunately, the formation of objects invoking poorly under- particular the results of the Planck mission, lend support to infl a- supergravité, qui repose sur quelques-unes des plus belles idées tions. Are black holes the simplest possible macroscopic objects? stood quantum effects is diffi cult to study. The collapse of scalar tionary models of the early universe. An elusive particle, the infl a- de la physique théorique, a dévoilé au fi l des années plusieurs de Do event horizons and black holes really exist, or is their formation fi elds, on the other hand, can theoretically allow boson stars to ton, could have driven this primordial acceleration, and although ses facettes. En particulier, la supergravité s’est révélée être une halted by some as-yet unknown mechanism? In addition, gravita- form, and these may become more compact and massive through our cur rent grasp of string theory does not allow a detailed analysis manifestation à faible énergie de la théorie des cordes, et un outil tional waves can tell us if gravitons are massless and if extra-light mergers. Interestingly, there is mounting evidence that compact of the problem, supergravity can provide fundamental clues on this essentiel pour l’étude des objets étendus appelés branes. S’il n’y degrees of freedom fi ll the universe, as predicted in the 1970s by objects without horizons but with a photosphere are unstable, rul- and the subsequent particle-physics epochs. a toujours pas de preuve de l’existence de la supersymétrie, la Peccei and Quinn in an attempt to explain the smallness of the neu- ing out entire classes of alternatives that have been put forward. Supersymmetry was inevitably broken in a de Sitter-like supergravité se porte toujours à merveille. tron electric-dipole moment, and more recently by string theory. Gravitational waves might soon provide a defi nite answer to such infl ationary phase, where superpartners of the infl aton tend to Ultralight fi elds affect the evolution of black holes and their grav- questions. Although current gravitational-wave detections are not experience instabilities. The novel ingredient that appears to Sergio Ferrara, CERN and INFN Frascati, and Augusto Sagnotti, Scuola itational-wave emission in a dramatic way that should be testable proof for the existence of black holes, they are a strong indicator that ▲ get around these problems is non-linear supersymmetry, whose Normale Superiore and INFN Pisa. with upcoming gravitational-wave observatories. photospheres exist. Whereas observations of electromagnetic

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Exotic phenomena Exotic phenomena

1.0 Gravitational lighthouses ● Further reading black hole 0.4 0.8 spin–0 Fur thermore, numerical simulations suggest that the super radiant A Arvanitaki et al. 2010 Phys. Rev. D 81 12350. 0.6 instability mechanism eventually causes a slowly evolving and R Brito et al. 2013 Phys. Rev. D 88 023514. 0.2 ringdown 0.4 non-symmetric cloud to form around the black hole, emitting V Cardoso et al. 2016 Phys. Rev. Lett. 116 171101.

radiation BH spin from 0.2 EM periodic gravitational waves like a gravitational “lighthouse”. S Giddings 2016 Class. Quant. Grav. 33 235010. GW signal 0.0 photosphere GW This would not only mean that black holes are not as simple as we P Pani et al. 2012 Phys. Rev. Lett. 109 131102. –0.2 0.8 spin–1 thought, but lead to a defi nite prediction: some black holes should N Yunes et al. 2016 Phys. Rev. D 94 084002. 0.6 be emitting nearly monochromatic gravitational waves whose exotic compact object 0.4 0.4 Résumé BH spin frequency is dictated only by the fi eld’s mass. This raises terrifi c 0.2 opportunities for gravitational-wave science: not only can gravi- Lier les ondes aux particules 0.2 radiation ringdown tational waves provide the fi rst direct evidence of ultralight fi elds from 0.8 spin–2 and of possible new effects near the horizon, but they also carry La découverte des ondes gravitationnelles par LIGO fournit GW signal 0.0 photosphere 0.6 detailed information about the black-hole mass and spin. If light l’indice le plus probant jusqu’ici de l’existence des trous noirs, mais –0.2 GW echo 0.4 BH spin fi elds exist, the observation of a few hundred black holes should ces distorsions de l’espace-temps ont bien d’autres choses à nous 0.2 show “gaps” in the mass-spin plane corresponding to regions apprendre. Elles nous offrent un moyen sans égal de vérifi er si les –10 0 10 20 30 40 0.0 where spinning black holes are too unstable to exist. trous noirs sont les objets macroscopiques les plus simples possible, time (ms) 100 102 104 106 108 1010 BH mass (M ) This is a surprising application of gravitational science, which si les horizons des événements existent vraiment, et si les gravitons Fig. 1. Typical gravitational-wave signal generated by a small can be used to investigate the existence of new particles such n’ont effectivement pas de masse. Élément peut-être encore plus star falling into a massive compact object with (top) and without Fig. 2. Exclusion plots in the black-hole mass-spin plane for as those possibly contributing to the dark matter. The idea of surprenant, les ondes gravitationnelles pourraient révéler la nature (bottom) a horizon. In the latter case, “echoes” of gravitational ultralight scalar (top), vector (middle) and tensor (bottom) fi elds, using observations of supermassive black holes to provide new de la matière noire et l’existence de champs scalaires légers – ce qui waves appear at late time and provide a smoking gun for showing electromagnetic (black) and gravitational-wave (red) insights not accessible in laboratory experiments would cer- établirait un lien entre la physique des particules et les objets les putative quantum effects that halt the gravitational collapse. observations. Above each curve (grey), superradiance would tainly be exciting. Perhaps these new frontiers in gravitational- plus extrêmes de l’Univers. spin the black hole down to the threshold, whereas below the wave astrophysics, in addition to probing the most extreme processes in the vicinities of black holes only probe the region curve accretion is dominant and there is no spin-down effect. objects, will also give us a clearer understanding of the micro- Vitor Cardoso, Universidade de Lisboa, and Paolo Pani, Sapienza outside of the photosphere, gravitational waves are sensitive to the CERN_125x193:Misescopic universe. en page 1 18/09/12 17:17 Page 1 University of Rome. entire space–time and are our best probe of strong-fi eld regions. hole’s kinetic energy, causing the spin of the black-hole to decrease. A typical gravitational-wave signal generated by a small star fall- Not only electromagnetic waves, but also gravitational waves and ing head-on into a massive black hole looks like that in fi gure 1. any other bosonic fi eld can be amplifi ed by a rotating black hole. In As the star crosses the photosphere, a burst of radiation is emitted addition, if the fi eld is massive, low-energy fl uctuations are trapped and a sequence of pulses dubbed “quasinormal ringing” follow, near the horizon and are forced to interact repeatedly with the black determined by the characteristic modes of the black hole. But if the hole, producing an instability. This instability extracts rotational star falls into a quantum-corrected or exotic compact object with energy and transfers it to the fi eld, which grows exponentially in www.goodfellow.com no horizon, part of the burst generated during the crossing of the amplitude and forms a rotating cloud around the black hole. For a photosphere refl ects back at the object surface. The resulting signal one-million solar-mass black hole and a scalar fi eld with a mass of in a detector would thus initially look the same, but be followed by 10 –16 eV, the timescale for this to take place is less than two minutes. lower amplitude “echoes” trapped between the photosphere and the Therefore, the very existence of ultralight fi elds is constrained by surface of the object (fi gure 1, lower panel). These echoes, although the observation of spinning black holes. With this technique, one Metals tricky to dig out in noisy data, would be a smoking gun for new phys- can place unprecedented bounds on the mass of axion-like particles, ics. With increasing sensitivity in detectors such as LIGO and Virgo, another popular candidate for dark matter. For example, we know observations will be pushing back the object’s surface closer to the from current astrophysical observations that the mass of dark pho- and materials horizon, perhaps even to the point where we can detect the echo of tons must be smaller than 10–20 eV, which is 100 times better than quantum effects. accelerator bounds. The technique relies only on measurements of the mass and spin of black holes, which will be known with unprec- for research Dark questions edented precision with future gravitational-wave observations. Understanding strong-fi eld gravity with gravitational waves can Superradiance, together with current electromagnetic obser- Goodfellow Cambridge Limited ON-LINE CATALOGUE also test the nature of dark matter. Although dark matter may vations of spinning black holes, can also be used to constrain Ermine Business Park interact very feebly with Standard Model particles, according the mass of the graviton, since any massive boson would trig- Huntingdon PE29 6WR UK to Einstein’s equivalence principle it must fall just like any other ger superradiant instabilities. particle. If dark matter is composed of ultralight fi elds, as recent Spin measurements of the Tel: 0800 731 4653 or +44 1480 424 800 studies argue, then black holes may serve as excellent dark-matter supermassive black hole in gal- Fax: 0800 328 7689 or +44 1480 424 900 detectors. You might ask how a monstrous, supermassive black Gravitational waves axy Fairall 9 requires the mass [email protected] hole could ever be sensitive to ultralight fi elds. The answer lies in can also test the of the graviton to be lighter superradiant resonances. When black holes rotate, as most do, they nature of dark than 5 × 10 –23 eV – an impres- display an interesting effect discovered in the 1970s called superra- sive number which is even diance: if one shines a low-frequency lamp on a rotating black hole, matter. more stringent than the bound 70 000 PRODUCTS SMALL QUANTITIES FAST DELIVERY CUSTOM MADE ITEMS the scattered beam is brighter. This happens at the expense of the recently placed by LIGO.

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a ppOintMEnts New management at linear collider K James/University of Oregon K James/University

Shinichiro Michizono from KEK has been LCC appointed as associate director for the International Linear Collider (ILC), taking over from Mike Harrison, while Jim Brau of the University of Oregon has replaced Hitoshi Yamamoto as associate director for physics and detectors. The Linear Collider collaboration, which encompasses the ILC and CLIC, has recently been granted a further three-year mandate by Multi Project Wafer (MPW) the International Committee for Future Accelerators.

Incoming associate directors Shinichiro Run for Silicon Radiation Detectors Michizono (left) and Jim Brau. ESO appoints astronomer LHC operations Prototyping service for silicon detectors Barcons as new director general changes hands

The council of the European Southern Rende Steerenberg has been appointed SINTEF Minalab MPW service offers prototyping We offer: Observatory (ESO), which builds and head of operations in CERN’s Beams of silicon detectors including strip detectors, pixel operates some of the world’s most powerful Department, effective from 1 January 2017.

ground-based telescopes, has appointed ESO/F J Carrera He takes over from Mike Lamont, who has detectors and PIN diodes. • Strip detectors Xavier Barcons as its next director general. been in the role since 2009 and oversaw The 57 year-old astronomer will take up his operations from the LHC’s rollercoaster By combining the orders from different customers into • Pixel detectors new position on 1 September 2017, when start-up to its latest record performance. a single wafer run, the fabrication costs are reduced • PIN diodes the current director general Tim de Zeeuw Lamont remains deputy group leader of the • From 1 to 6 wafers completes his mandate. He began his career as Beams Department. significantly. The cost savings start at around 50 % and a physicist, completing a PhD on hot plasmas. can be as high as 80 %. • 5-layer process incl. passivation N Steerenberg • Detector thickness 300 µm to 1 mm Xavier Barcons will become the new Individual wafers and a separate photomask set are • 50 to 80 % savings on fabrication cost ESO director later in the year. used for each customer, thereby ensuring flexibility and confidentiality. Between 1 and 6 wafers can be ordered Next theory leader for Jefferson Lab per customer.

In October 2016, Jianwei Qiu joined the

The detectors are fabricated on high-quality 150 mm JLAB An unique opportunity to benefit from Thomas Jefferson National Accelerator diameter FZ silicon wafers. Wafer thicknesses from SINTEF’s 35 years experience in the field Facility as its new associate director for 300 µm to 1 mm are available for individual selection. theoretical and computational physics. Our full field wafer size lithography allows maximum of silicon radiation detector development, Qiu, whose research focus is QCD and its flexibility for the layout. Different detector types prototyping and production! applications in both high-energy particle and nuclear physics, will oversee a broad and test structures can be combined onto a single programme of theoretical research in photomask set. support of the physics studied with the Continuous Electron Beam Accelerator Prices and time schedule on request : [email protected] Facility (CEBAF). Qiu, who previously led the nuclear theory Rende Steerenberg, previously deputy group at Brookhaven National Laboratory. operations group leader.

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Untitled-1 1 30/09/2016 14:07 CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Faces & Places Faces & Places

a W a r D s CERN Neutrino physicist Russian Academy of Sciences elects Heuer given highest French honour takes up Pascal Chair theorists as latest new members

Former CERN Director-General Rolf-Dieter SESAME Council, among other roles, was Heuer has been appointed Chevalier de la presented with the medal on 22 November Fumihiko In late 2016, theorists Mikhail Danilov, from the University of California in Santa Barbara Légion d’Honneur (Knight of the Legion at the residence of the French permanent Suekane wins the Lebedev Institute in Moscow, Sergio were elected as members of the Russian of Honour), one of the highest recognitions representative in Geneva. the French Ferrara from CERN and David Gross from Academy of Sciences. Established in 1724, of achievement in France. Heuer, who is award. the Kavli Institute for Theoretical Physics and the body has more than 2000 members. currently president of the German Physical Rolf Heuer with French ambassador

Society (DPG) and president-elect of the Elisabeth Laurin. RCNS/Tohoku University Getty images Getty String theorists snare PT2026 NMR Precision Teslameter Breakthrough Prize Fumihiko Suekane of Tohoku University, Reach new heights The 2017 Breakthrough Prize in Japan, has been awarded a 2016 Blaise Pascal Fundamental Physics has been awarded to Chair to further his research into neutrinos. Joseph Polchinski, University of California Established in 1996, and named after the in magnetic eld at Santa Barbara, and Andrew Strominger 17th-century French polymath Blaise Pascal, and Cumrun Vafa of Harvard University. the ¤200,000 grant allows researchers from measurement The three winners, who received the $3 abroad to work on a scientifi c project in an million award at a glitzy ceremony in San institution in the Ile-de-France region. Suekane Francisco on 4 December, have made Andrew Strominger, Joseph Polchinski and Cumrun Vafa (left to right) at the award ceremony. will spend a year working at the Astroparticle The Metrolab PT2026 sets a new important contributions to fundamental and Cosmology Laboratory in Paris, where he standard for precision magnetometers. physics including quantum gravity and Ronald Drever and Kip Thorne of Caltech Berkeley); Simone Giombi (Princeton will focus on R&D for novel neutrino detectors Leveraging 30 years of expertise building string theory. Polchinski was recognised and Rainer Weiss of MIT, who were University) and Xi Yin (Harvard University); and measurements of reactor neutrinos. in particular for his discovery of D-branes, recognised in May along with the entire and Frans Pretorius (Princeton). the world’s gold standard magnetometers, while the citation for Strominger and Vafa LIGO team for the discovery of gravitational This year’s Breakthrough Prize, which V i s i t s it takes magnetic  eld measurement to included their derivation of the Bekenstein– waves – were also present. A further prize, was founded in 2012 by Sergey Brin, Anne new heights: measuring higher elds with Hawking area-entropy relation, which the $100,000 New Horizons in Physics Wojcicki, Yuri and Julia Milner, Mark unifi ed the laws of thermodynamics and Prize, went to six early-career physicists: Zuckerberg and Priscilla Chan, saw $25 better resolution. black-hole dynamics. Asimina Arvanitaki (Perimeter Institute), million in prizes awarded for achievements M Brice/CERN Recipients of the previously announced Peter Graham (Stanford University) and in the life sciences, fundamental physics and The PT2026 offers unprecedented  exibility Special Prize in Fundamental Physics – Surjeet Rajendran (University of California, mathematics. in the choice of parameters, interfacing Humboldt award for Atomic pioneer wins presidential medal and probe placement, as well as greatly improved tolerance of inhomogeneous Brookhaven physicist US physicist and science policy adviser The White House President of the Republic of Poland, elds. And with Ethernet & USB interfaces to the US government, Richard Garwin, Andrzej Duda, visited CERN on 15 November and LabVIEW software, it  ts perfectly into On 30 November, the Alexander von was awarded the Presidential Medal of and toured the CERN Control Centre. modern laboratory environments. Humboldt Foundation in Bonn, Germany, Freedom at a White House ceremony on

granted a Humboldt Research Award to Raju 22 November. The award is the highest le - Photo: Scott Maxwell, Master www.agence-arca.com Venugopalan, a senior physicist at Brookhaven honour that the US government can confer National Laboratory and Stony Brook to civilians. Garwin was recognised for University. The ¤60,000 award recognises his long career in research and invention,

Venugopalan’s achievements in theoretical which saw him play a leading role in the Bennett/CERNS nuclear physics, and comes with the opportunity development of the hydrogen bomb, and for to collaborate with German researchers at his advice to policy makers. Heidelberg University and elsewhere. Introducing Garwin, President Obama remarked: “Dick’s not only an architect of

BNL the atomic age. Reconnaissance satellites, the MRI, GPS technology, the touchscreen all bear his fi ngerprints – he even patented

a mussel washer for shellfi sh. Dick has Pantone 286 Pantone 032 advised nearly every president since Director of SLAC National Accelerator Laboratory Eisenhower, often rather bluntly. Enrico in the US, Chi-Chang Kao, signed the guestbook Fermi, also a pretty smart guy, is said to with CERN Director-General Fabiola Gianotti on have called Dick the only true genius he Richard Garwin was one of 21 recipients of 23 November. Magnetic precision has a name www.metrolab.com Venugopalan joined Brookhaven in 1998. ever met.” the 2016 Presidential Medal of Freedom.

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Faces & Places Faces & Places S Ritt/PSI C O n F E r E n C E s measurements of beta-decay correlations and searches for exotic interactions. The future European Spallation Source in Triangulating in Mumbai Sweden will also allow a new and much improved search for neutron–antineutron From 28 November to 2 December, more oscillations. Atomic physics and related than 200 fl avour physicists gathered at the methods offer unprecedented sensitivity Tata Institute of Fundamental Research in to fundamental-physics aspects ranging Mumbai for the 9th International Workshop from QED tests, parity violation in weak on the Cabibbo–Kobayashi–Maskawa interactions, EDM and exotic physics to Unitarity Triangle (CKM2016). The dark-matter (DM) and dark-energy searches. TIFR Photography SectionTIFR Photography workshop focuses on weak transitions With the absence of signals from direct DM Attendees enjoy a music event at PSI2016, which comprised 65 plenary talks. of quarks from one fl avour to another, as searches so far, light and ultralight DM is described by the CKM matrix, and on the a focus of several upcoming experiments. (μ → e conversion) devoted to muons and C O r r E C t i O n charge–parity (CP) violation present in these Atomic physics also comprises precision their lepton-fl avour violating decays, and transitions, as visualised by the unitarity spectroscopy of exotic atoms, and several the upcoming muon g-2 experiments at The Compiler’s Note in the December 2016 triangle (UT). Input from theory, particularly highlight talks included the ongoing efforts FNAL and J-PARC have reported impressive issue of the Courier (p50) inadvertently lattice QCD, is vital to fully leverage the CKM2016 participants at the Tata Institute of Fundamental Research in Mumbai. at CERN’s Antiproton Decelerator with progress. Last but not least, rare kaon decays reported that the touchscreen and tracker power of such measurements. antihydrogen and with light muonic atoms (at CERN and J-PARC), new long-baseline ball used at the SPS were inventions of an

It is an exciting time for fl avour physics. The excluded at CL > 0.95 ultimately expected to increase the size of at J-PARC and at PSI. For antiprotons neutrino oscillation results, developments individual. excluded area has CL > 0.95 mass scales potentially involved in such weak γ the LHCb data samples by approximately and nuclei, impressive results from recent towards direct neutrino-mass measurements, Such projects are, of course, team efforts, processes are much higher than those that a factor four. Longer term, the Belle II Penning-trap mass and g-factor measurements and CP and CPT tests with B mesons were sometimes involving industry, and useful Δmd & Δm s can be directly probed at the LHC, due to the sin 2β experiment based at the SuperKEKB were presented with impacts on CPT tests, reported. The fi eld of low-energy precision products emerge and evolve over time and

presence of quantum loops that mediate many– collider recently enjoyed its fi rst beam, and bound-state QED tests and more. physics has grown fast over the past few place. Credit should have been more fairly 0 0 Δmd of the processes of interest, such as B(s) – B(s) εK α will begin its full physics programme in Major international efforts are under way years, and participants plan to meet again at attributed to refl ect the history of these mixing. Compared with the absence of new γ β 2018. By 2024, Belle II should have collected at PSI (μ → eγ, μ → eee), FNAL and J-PARC PSI in 2019. important CERN devices. particles so far at the energy frontier, LHCb α 50 times more data than Belle, allowing V and other B factories already have signifi cant ub α unprecedented tests of rare B-meson decays hints of deviations between measurements and precision CP-violation measurements. Nanotechnology meets HEP in Darmstadt and Standard Model (SM) predictions. γ εK On the same timescale, the LHCb upgrade CKM An example is the persistent discrepancy f i t t e r sol. w/cos 2β < 0 will also be in full swing, with the goal of EPS 15 (excl. at CL > 0.95)

in the measured differential distributions increasing the data size by least a factor The fi elds of nanomaterials and GSI of the decay products of the rare 10 compared to Run 1 and Run 2. Plans nanotechnology are quickly evolving, with fl avour-changing neutral-current process The sides, angles and height of the for a second LHCb upgrade presented at discoveries frequently reported across B0 → K*0 μ+ μ–, fi rst reported by the LHCb unitarity triangle constitute a highly the meeting would allow LHCb, given the a wide range of applications including collaboration in 2015. A highlight of overconstrained system where small long-term future of the LHC, to run at much nanoelectronics, sensor technologies, drug CKM2016 was the presentation of fi rst deviations from predictions would indicate higher instantaneous luminosities to yield an delivery and robotics, in addition to the results of the same distributions from the presence of non-SM physics. enormous data set by 2035. energy and healthcare sectors. the Belle experiment in Japan, which With more data the puzzles of fl avour At an academia–industry event on 20–21 also included the related but previously time-dependent CP violation in the decay physics will be resolved thanks to the October at GSI in Darmstadt, Germany, 0 *0 + – 0 unmeasured process B → K e e . The of Bs mesons in two separate fi nal states, ongoing programme of LHCb, imminent co-organised by the technology-transfer + – + – Belle results are more compatible with those Ds K and K K . The latter involves loop results from rare-kaon-decay experiments network HEPTech, delegates explored novel of LHCb than the SM, further supporting the diagrams allowing a new-physics-sensitive (KOTO and NA62), and the Belle II/LHCb connections between nanotechnology and idea that new physics may be manifesting determination of a UT angle (γ) that can be upgrade projects. No doubt there will be high-energy physics (HEP). itself, via interference effects, in these compared to a tree-level SM determination more revealing results by the time of the next The forum included an overview observables. Progress on measuring CP in the decay B– → D0 K–. CKM workshop, to be held in Heidelberg in of the recent experiments at DESY’s violation in B decays was also reported, For the fi rst time, LHCb also presented September 2018. hard X-ray source PETRA III, which with LHCb presenting the fi rst evidence for results with data from LHC Run 2, which is ● www.tifr.res.in/~ckm16. allows the investigation of physical and 70 participants from 11 countries attended the event and 30 bilateral meetings took place. chemical processes in situ and under working conditions and serves a large the core of which are nano-structured Characterisation of Grenoble. PSI event probes the low-energy frontier user community in many fi elds including tungsten-carbide-based coatings that have The meeting addressed how collaboration nanotechnology. Thermal-scanning probe promising applications in HEP and vacuum between academia and industry in the lithography, an increasingly reliable method engineering. Industry also presented nanotechnology arena can best serve the While there are many conferences focusing PSI2016, took place from 16–21 October anomalies presently seen in B decays. On the for rapid and low-cost prototyping of 2D ion-track technology, which is being used needs of HEP, with CERN presenting on physics at the high-energy frontier, the and attracted more than 170 physicists. experimental side, several new results were and quasi-3D structures, was also discussed. to synthesise 3D interconnected nanowire applications in gaseous detectors using the triennial PSI workshop at the Paul Scherrer Theoretical overviews covered: precision presented. Much attention was paid to the production networks in micro-batteries or gas sensors, charge-transfer properties of graphene. Institute (PSI) in Switzerland concerns QED calculations; beyond-the-Standard- Fundamental neutron physics and application of nanostructures, where among other applications. Neutron-research The technology-transfer offi ce at DESY searches for new phenomena at non-collider Model implications of electric-dipole- featured prominently, ranging from the achievements of the Ion Beam Center at infrastructures and large-scale synchrotrons also shared its experience in developing experiments. These are complementary to moment (EDM) searches; axions and other cold-neutron-beam experiments to those with Helmholtz-Zentrum Dresden-Rossendorf in are emerging as highly suitable platforms for a marketing strategy for promoting direct searches at the LHC and often cover a light exotic particles; fl avour symmetries; stored ultracold neutrons at facilities such as surface nanostructuring and nanopatterning the advanced characterisation of micro- and the services of the DESY NanoLab to parameter space that is beyond the reach of the muon g-2 problem; NLO calculations of ILL, PSI, LANL, TRIUMF and Mainz. Key were introduced. nano-electronic devices, and the audience companies. Both academia and industry the LHC or even future colliders. the rare muon decay μ → eeeνν; and possible experiments are measurements of the neutron UK fi rm Hardide Coatings Ltd presented heard the latest developments from the representatives left the event with a set of The fourth workshop in this series, models to explain the exciting fl avour lifetime, searches for a permanent EDM, its advanced surface-coating technology, IRT Nanoelec Platform for Advanced contacts and collaboration arrangements.

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Faces & Places Faces & Places Super future for medical accelerators Hard probe for QCD matter Xi-Chang Chen Xi-Chang

On 24–25 November, academics and leading PSI presented medical accelerators such as the The 8th International Conference on Hard companies in the fi eld of superconductivity MEVION S250 – a proton-therapy system and Electromagnetic Probes of High-energy met in Madrid, Spain, to explore the based on a gantry-mounted 250 MeV Nuclear Collisions (Hard Probes 2016) technical challenges of applying new superconducting synchrocyclotron that was held in Wuhan, China, on 23–27 accelerator technology to medicine. weighs less than 15 tonnes and generates September. Hard and electromagnetic Organised by CIEMAT in collaboration magnetic fi elds in excess of 10 T. Global probes are powerful tools for the study of with HEPTech, EUCARD2, CDTI, GSI medical-technology company IBA the novel properties of hot and dense QCD and the Enterprise Europe Network, the described its two main superconducting matter created in high-energy nucleus– event brought together 120 participants cyclotrons for particle therapy: the nucleus collisions, and have provided much from 19 countries to focus on radioisotope Cyclone 400 for proton/carbon therapy important evidence for the formation of production, particle therapy and gantries. and the S2C2 dedicated to proton quark–gluon plasma (QGP) in heavy-ion Hard Probe 2016 attracted a record number of participants. Superconductivity has a range of therapy, with a particular emphasis on collisions at RHIC and the LHC. applications in energy, medicine, fusion their superconducting coil systems. IBA Hard Probe 2016 attracted close to 300 excitations; jet properties in small ATLAS, CMS, LHCb, PHENIX and STAR and high-energy physics (HEP). The latter also introduced the latest developments participants from 28 countries. The main systems; heavy fl avour hadrons and collaborations, together with many new are illustrated by CERN’s high-luminosity concerning ProteusONE – a single-room topics discussed were: jet production quarkonia; photons and dileptons and exciting theoretical and phenomenological LHC (HL-LHC), now near construction system that delivers the most clinically and modifi cation in QCD matter; high initial states and related topics. The most developments, were discussed. The next with superconducting magnets made from advanced form of proton-radiation transverse-momentum hadron spectra recent experimental progress on hard and Hard Probe conference will be held in Aix

advanced Nb3Sn technology capable of therapy. Researchers from MIT in the US and correlations; jet-induced medium electromagnetic probes from the ALICE, Les Bains, France, in 2018. 12 T fi elds. The HL-LHC demands greatly presented a novel compact superconducting advanced superconducting cavities with synchrocyclotron based on an ironless more effi cient and higher-gradient RF A proton-therapy gantry facility at the magnet with a much reduced weight, while Exotic nuclei and super-heavy elements systems, plus the development of new Paul Scherrer Institute. the TERA Foundation in Italy is developing devices such as crab cavities that can defl ect superconducting technology for “cyclinacs” or rotate single bunches of protons. these isotopes in addition to 68Ga. Antaya – accelerators that combine a cyclotron The International Symposium on EXOtic is an experiment on the synthesis of element On the industry side, new Science and Technology, meanwhile, injector and a linac booster. Nuclei (EXON-2016), took place from JINR 117 held at the cyclotron of JINR. Recently, superconducting technology is ready to go reported on the development of a portable Finally, the session on gantries covered 5–9 September in Kazan, Russia, attracting the International Union of Pure and Applied into production for medical applications. high-fi eld superconducting cyclotron for developments such as a superconducting around 170 nuclear experts from 20 Chemistry approved the discovery of the A dedicated session presented novel the production of ammonia-13N in near bending-magnet section for future countries. The scientifi c programme focused new elements with atomic numbers 113 developments in cyclotron production, proximity to the PET cameras. The meeting compact isocentric gantries by researchers on recent experiments on the synthesis (“nihonian”), 115 (“moscovium”), 117 illustrated by the AMIT project of also heard from MEDICIS, the new facility at the Paul Scherrer Institute, and a and study of new super-heavy elements, (“tennessine”) and 118 (“oganesson”). CIEMAT (based on a cyclotron with a under construction at CERN that will superconducting rotating gantry for carbon the discovery of which demonstrates the Five laboratories, which are the compact superconducting design that will extend the capabilities of the ISOLDE radiotherapy designed by the Japanese effi ciency of international co-operation. co-founders of the symposium, are now be able to produce low-to-moderate rates radioactive ion-beam facility for production National Institute of Radiological Sciences. Interesting results were obtained in joint creating a new generation of accelerators for of dose-on-demand 11C and 18F) and the of radiopharmaceuticals and develop With demand for medical isotopes and experiments on chemical identifi cation of the synthesis and study of new exotic nuclei. French industry–academia LOTUS project new accelerator technologies for medical advanced cancer therapy rising, we can elements 112 and 114 performed at JINR Projects such as SPIRAL2, RIKEN RI Beam system, which features a compact 12 MeV applications (CERN Courier October look forward to rich collaborations between (Russia), the GSI (Germany) and the Paul Factory, FAIR, DRIBs, NICA and FRIB will superconducting helium-free magnet 2016 p28). accelerator physics and the medical Scherrer Institute (Switzerland). A vivid Participants of the VIII International allow us to delve further into the upper limits cyclotron suitable for the production of Concerning particle therapy, industry community in the coming years. example of co-operation with US scientists Symposium on EXOtic Nuclei. of the periodic table. Higgs Couplings 2016 R Kish/SLAC

The fi fth in the series of Higgs Couplings Thaler Tamas workshops, which began just after the Higgs-boson discovery in 2012 to bring together theorists and experimentalists, was held at SLAC on 9–12 November and drew 148 participants from fi ve continents. Higgs experts from theory and experiment at Higgs Couplings 2016. Discussions focused on lessons from the current round of LHC analyses that could be Two new themes emerged at the meeting. also debated the application of effective fi eld applied to future data. Modelling of signal The fi rst was the possibility of exotic decays theory as a framework for parametrising and background is already limiting for some of the 125 GeV Higgs boson. These include precise Higgs measurements. The CERN Accelerator School (CAS) and the Wigner Research Centre for Physics jointly organised an introduction-to-accelerator-physics measurements, and new theoretical results not only Higgs decays to invisible particles The 6th Higgs Couplings meeting will be course in Budapest, Hungary, from 2–14 October, attended by more than 120 participants spanning 28 nationalities. This year, CAS will and strategies were presented. Other key but also decays to lighter Higgs particles, light held in Heidelberg on 6–10 November 2017. organise a specialised course on beam injection, extraction and transfer (to be held in Erice, Sicily, from 10–19 March) and a second issues were the use of vector-boson fusion quarks and leptons (possibly with fl avour We look forward to new ideas for the creative specialised course on vacuum for particle accelerators (near Lund, Sweden, from 6–16 June). The next course on advanced-accelerator production as a tool, and the power and violation) and new, long-lived particles. A use of the large data samples of Higgs bosons physics will be held in the UK in early September, and a Joint International Accelerator School on RF technology will be held in Hayama, complementarity of diverse searches for number of searches from ATLAS and CMS that will become available as the LHC Japan, from 16 –26 October (www.cern.ch/schools/CAS). heavy Higgs bosons. reported their fi rst results. The workshop programme continues.

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Faces & Places Faces & Places

O B i t u a r i E s Ovsat Abdinov 1944–2016 Valery Khovanskiy 1940–2016 Russian physicist Valery Dmitrievich the search for new particles and neutrino Ovsat Abdinov, member of the Azerbaijan scientists in the LHC, but this did not Khovanskiy passed away in Moscow oscillations. From 1990 onwards, he National Academy of Sciences (ANAS), interrupt connections with Dubna: Abdinov on 7 September. A veteran of Russian participated in the ATLAS experiment. His

died on 29 October at the age of 72, after a Gökhan Ünel was a staff member of JINR, deputy of experimental high-energy physics and group was active in the preparation of the long illness. He was born in Belokan city, authorised representative of the government long-time leader of the ITEP team in Letter of Intent, working on the concept of Azerbaijan, graduated from Baku State of Azerbaijan Republic in JINR, and a ATLAS, he will be remembered not only radiation-resistant forward calorimeters, University in 1966, and defended his PhD member of JINR Scientifi c Council. as an energetic contributor to the CERN and, from 1995 to 2009, worked on the thesis in 1972. The creation of Azerbaijan’s fi rst neutrino and LHC programmes, but also as construction and commissioning of the It is impossible to overstate the impact that Worldwide LHC Computing Grid segment an honest and principled person who loved ATLAS liquid-argon forward calorimeters, Abdinov had in the creation and development also owes its thanks to Abdinov. science and life. providing the major part of the tungsten of high-energy physics in Azerbaijan. His Abdinov was a famous scientifi c Valery was born in Sverdlovsk in the electrodes. wide knowledge, inexhaustible energy, representative of the Azerbaijan former USSR, and received his PhD From 1995 to 2012, Valery was the leader talent in organisation and search for young intelligentsia. He was an organiser and (for the study of cumulative effects of the neutrino-physics laboratory at ITEP. He specialists led to the creation of his own invited speaker at international conferences, in πN-interactions) at the Institute of served on the LHCC from 1992 to 1994 and school in this fi eld that serves as an example Ovsat Abdinov had a major impact on a presenter of high-level reports and the Experimental and Theoretical Physics Khovanskiy at CERN in the late 1990s. for a long period on the Russian government’s for future generations. high-energy physics in Azerbaijan. winner of numerous research grants both in (ITEP, Moscow) in 1969. Since then, his commission on fundamental research. He was Scientifi cally, Abdinov’s main interest was the former Soviet Union and in Azerbaijan. main scientifi c interests were in the fi elds of interactions to validate the then very young also one of the founders and lecturers of the the theoretical description of hadron-nuclear for Nuclear Research (JINR) in Dubna and He dedicated almost 20 years of his neutrino physics, novel particle-detection quark-parton model. In the late 1970s, famous ITEP Winter School of Physics. interaction processes. He was the fi rst the Institute of High Energy Physics (IHEP) scientifi c activity to investigations carried methods and hadron collider physics. Valery joined the CERN experimental Valery had a vivid individuality and was to propose a hypothesis of the cluster in Serpukhov, both in Russia, followed by out within the ATLAS collaboration. We In the fi rst Russian accelerator neutrino neutrino programme at the SPS and PS, invariably good humoured. His many pupils, formation in light nuclei, which was later CERN. hope that his work will be continued by experiment at the Serpukhov 70 GeV proton and became one of the senior scientists colleagues and friends admired him and he experimentally proven. The laboratory The creation and expansion of relations his scientifi c heirs and further benefi t synchrotron (IHEP-ITEP, 1970–1978), of the CHARM, PS-181, CHARM-2 will be very much missed. he headed at ANAS Institute of Physics between Azerbaijan and CERN paved the Azerbaijan high-energy physics. Valery lead the detector construction and CHORUS experiments devoted to a ● His friends and colleagues, ITEP and collaborated initially with the Joint Institute way for the participation of Azerbaijan ● His colleagues. and studied neutrino and antineutrino systematic study of neutral currents, and ATLAS. Malcolm Derrick 1933–2016 Ted Wilson 1938–2016

Malcolm Derrick, a long-time leader in ANL produced by the MINOS programme is the Edmund (Ted) Wilson, a well-known fi gure Ted was a natural and gifted teacher. the Argonne high-energy physics (HEP) direct result of these early experiments. in the world of particle accelerators and During the days of SPS construction he ran

division, passed away on 31 October After the closure of the ZGS programme, former director of the CERN Accelerator WilsonAlex a series of courses on accelerator theory for after a long illness. Born in Hull, UK, in Malcolm initiated Argonne participation School (CAS), died after a short illness on members of the 300 GeV laboratory, which 1933, Malcolm received his BSc and PhD in two important experiments: HRS at the 3 November. evolved into the book An Introduction degrees in physics from the University PEP collider at SLAC, where he proposed The son of a schoolteacher in to Particle Accelerators. Following his of Birmingham. After working on the using the superconducting magnet of the Liverpool, UK, he graduated in physics appointment as CAS director in 1992, he cyclotron at Carnegie Tech, he moved to 12 foot bubble chamber as the solenoid at the University of Oxford in 1959 and was responsible for organising 25 schools, Oxford University in 1962 to help establish for the HRS spectrometer, and the ZEUS immediately joined the nearby Rutherford in addition to special schools in India, a bubble-chamber group working at CERN. experiment at the HERA collider in DESY. Appleton Laboratory. His fi rst stay at China and Japan. He also coauthored a In 1963 he moved to Argonne National Malcolm took sabbatical leave at University CERN was in 1962–1963 and he returned fascinating book on the history of particle Laboratory to work on the 12 GeV ZGS College London and later at DESY, where in 1967 as a fellow, working in Werner accelerators and their applications: Engines synchrotron then in construction. he served as physics chairman and oversaw Hardt’s group on the design of the of Discovery, a Century of Particle While working on several bubble-chamber such activities as physics publications. A booster for the new large synchrotron: Accelerators. experiments with the 30 inch chamber, gifted speaker, he served on several review the “300 GeV” machine, later to become Accelerator physicist Ted Wilson. On his retirement, Ted renewed his Malcolm’s main interest was in establishing Malcolm Derrick was a long-time CERN committees and was a HEPAP member the Super Proton Synchrotron (SPS). He association with Oxford University by a programme of neutrino physics using the collaborator. and an active participant in the Snowmass became the right-hand man of John Adams essential for the smooth commissioning of becoming a guest professor at the John 12 foot bubble-chamber then being built. Conferences. He retired in 2006. in 1969, helping him to prepare the project the SPS, for which he was responsible a few Adams Institute of Accelerator Physics, He was spokesman for the fi rst experiment supported the division's collaboration Besides being a brilliant physicist, for approval by CERN Council, which years later. Following the approval in 1978 where he taught and supervised students. He using the deuterium-fi lled chamber, which with the University of Minnesota to Malcolm had a knack for entertaining his was given in 1971. He became one of the of the bold proposal of Carlo Rubbia to turn has helped to bring on a new generation of produced several important results including build an underground detector to search guests with stories about his life and endless fi rst staff members of the new “300 GeV the SPS into a part-time proton–antiproton machine builders. the fi rst measurement of the axial-vector form for proton decay in the Soudan Mine anecdotes about history and philosophy. His laboratory” set up for the construction of collider, Ted started working on how to Ted Wilson will be sorely missed by the factor in muon neutrino–neutron quasi-elastic in Minnesota. This resulted in a rich spare time was spent reading good books, the SPS. convert the machine from a synchrotron to a world’s accelerator community. He will scattering. This result was verifi ed by later programme of neutrino physics with a fi ne dining and listening to classical music. In 1973–1974, at the request of Adams, storage ring. He later worked on the design always be remembered for his impish smile BNL and FNAL experiments. series of multi-kiloton detectors and in new Malcolm leaves behind his wife Eva and his Ted spent a sabbatical year at Fermilab to and construction of CERN’s antiproton and his dry sense of humour. He is survived Malcolm served on two occasions as HEP underground laboratories at Soudan, using many children and grandchildren. He will be work on the commissioning of the “main complex: fi rst the antiproton accumulator, by his wife Monika, his three children and division director and was always a source both atmospheric neutrinos and Fermilab missed by all who knew and loved him. ring”, a machine very similar to the SPS. to which a second ring, the antiproton fi ve grandchildren. of good career advice. He enthusiastically neutrino beams. The important physics ● His colleagues. The lessons he learnt there would prove collector, was later added. ● His friends and colleagues.

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 Recruitment Beam Physicist CERN Experimental Areas Group 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 . A new year, a new challenge? Set up, adapt and develop particle beams. Participate in the design of experimental facilities. Collaborate and guide the operations team to optimally exploit the beam lines according to the needs of experiments. If you are an experienced physicist interested in both particle and accelerator physics who would relish this challenge, join CERN’s Experimental Areas Group. The Neutron Sciences Directorate invites applicants for CERN: Take part in great times with `Physics Beyond Colliders’which brings in many new ideas Research Accelerator Division Director (RAD) for experiments and beam lines! In this executive leadership role, you will lead an organization of approximately 240 Deadline for applications: 12th February 2017 staff and $93M in annual funding to enable neutron science research in support of Department of Energy (DOE) missions. The RAD Director reports to the Associate Laboratory Director for Neutron Sciences and represents the ORNL core capability of accelerator science and technology. This position also directs the technical initiatives necessary to maintain pre-eminent standing in high power hadron linear accelerators, and supports cutting edge neutron scattering science. Broad experienceexperien in both accelerator science and operations in a fast-paced, multi-disciplinary environment is essential. The successful candidate will be expected to ensure the Spallation Neutron Source accelerator and target complex maintain a world-leading position in pulsed accelerator-based neutron sources by sustaining highly reliable operation (>90% against schedule) for over 5000 hours per year at a beam power of 1.4 MW, and contribute to projects aimed at doubling Visit beam power and neutron scattering capacity. for your next career move To apply to this position, please visit neutrons.ornl.gov/careers and reference posting # NB50608623

Oak Ridge National Laboratory is managed by UT-Battelle for the US Department of Energy. 16-G01844/gim

WE ARE HIRING The jobs site Pontificia Universidad Catolica de Chile RESEARCH ENGINEER (MAGNET ENGINEERING) Two Faculty Positions in experimental or computational Plasma Physics for physics and Read more about the position $Attractive | South America | 07 Dec 2016 engineering at www.maxlab.lu.se/career

The Institute of Physics of the Pontificia Universidad Católica de Chile invites applications for two tenure-track faculty positions at the Assistant Professor level, to begin as early as August 2017. A Ph. D. degree in physics is required and postdoctoral experience is expected. The successful candidate is expected to establish a leading research program in the areas relevant to the Plasma Physics group, as well as teach at the undergraduate and graduate levels. One of the selected candidates is expected to develop research in experimental Plasma Physics, with particular emphasis in dense transient plasmas. A good working knowledge of pulsed power technology and electronics together with plasma diagnostics is advantageous. The area of research expertise of the second selected candidate could be either in experimental plasma physics applied to materials science or biomedicine, or to computational Plasma Physics related to transient high energy density plasmas. Applications should include a letter of application, curriculum vitae, list of publications, and statements of past and proposed research and teaching interests. Furthermore, at least two confidential letters of reference must be sent The jobs site for physics The jobs site directly by the referees. All the documents should be sent by email before February 28, 2017 to the Head of the More than Selection Committee, Prof. Heman Bhuyan, [email protected]. and engineering for physics and engineering 23 000 58 The jobs site for monthly unique physics and visitors engineering CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017

Call to scientific institutes for collaboration in the context of the Beamline for Schools competition at CERN

Call to scientific institutes for collaboration in the context of the For further information, interested institutes may contact: Beamline for Schools competition at CERN [email protected] In 2017 CERN will, for the fourth time, organize a Beamline for Details about the competition itself can be found at: Schools (BL4S) Competition that invites high school students www.cern.ch/bl4s from around the world to make a proposal for an experiment at a beam line of the PS accelerator. In the framework of this project, CERN invites scientific institutes to participate in the organization of the competition by contributing the expertise of two young researchers (physicist, computer scientist or engineer) for the period from 1 February 2017 to 30 September 2017, subject to a possible extension. A detailed description of the project and the qualification and skills required from the young researchers can be found at: http://cern.ch/go/tdD8 The modalities of the proposed collaboration will be set out in a dedicated agreement between CERN and the institute(s) concerned.

INTERNATIONAL SELECTION PROCESS FOR ELI BEAMLINES FACILITY IN CZECH REPUBLIC GraduateCareers LEADER OF RESEARCH PROGRAMME 2 X-ray sources driven by ultrashort laser pulses

The suitable candidate will be responsible for the delivery of X-ray sources driven by ultrashort laser pulses and their integration into the March 2017 ELI Beamlines facility.

The candidates are expected to comply with the following requirements: 1. PhD in the field of laser plasma physics Target the best candidates for your 2. Post-doc in laser driven X-ray sources would be a plus graduate vacancy 3. Working experience of minimum 5 years in the field of laser driven X-ray sources with an excellent record of publications in this field in international peer-reviewed journals 4. Working experience in management of a larger research group Contact Natasha Clarke today to find out 5. Willing to travel and English language on a very good level (written and spoken) how to get your vacancy noticed.

Location: ELI Beamlines, Institute of Physics ASCR, Dolní Břežany, Czech Republic E-mail [email protected] Applicants should provide their CV and cover letter (in English) along with a complete list of publications. They should single out 5 most important publications with the description of their contribution. All these materials should be sent to [email protected]. The deadline for applications is open. Tel +44 (0) 117 930 1864 Please include the following text in your cover letter, to allow us to process your personal details:

I agree that, according to the decree 101/2000 coll. (Czech Republic), my personal details sent to FZU AV CR, v.v.i., Na Slovance 2, 18221 Praha 8, Czech Republic can be used for the purpose of obtaining employment and management of database of employment candidates. This permission is given for the period of one year and can be at any time withdrawn by giving a notice in writing.

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C OMPILED BY V IRGINIA G RECO, CERN

Particle Physics in the LHC Era scattering, the quark–parton model and By G Barr, D Devenish, R Walczak and T Weidberg neutrino interactions, and concludes its fi rst Oxford University Press part with electron–nucleon deep inelastic This book’s aim, as stated in the scattering. This is a departure from standard introduction, is to provide a practical practice in most textbooks. The second introduction to particle physics in the LHC part of the chapter is on the introduction of era at the level of an advanced undergraduate colour, QCD, parton distribution functions or introductory graduate course. Indeed, and hadron–hadron collisions, and the Technology at your fingertips in its almost 400 pages, it covers a wide Drell–Yan process. The material, which is range of topics, from instrumentation extensive but presented quite briefl y, is more and detector technologies to some appropriate for undergraduates. mathematical techniques and the traditional Chapters 10 (oscillations and CP particle-physics topics that are usually violation in meson systems) and included in similar textbooks. It hovers, by 11 (neutrino oscillations) are great design, at the border between the established introductions to physics mixing, both in the textbooks aimed at undergraduates and the quark and the lepton sector. The discussion Technology more advanced graduate texts that often in chapter 10 is modern, with results from start with quantum fi eld theory. experiments at LEP, the B factories and Following the introduction, the book hadron colliders. Chapter 11 has one of the at your fingertips commences with a three-chapter sequence best summaries on neutrino physics for with somewhat technical content. Chapter 2, this level: it starts with the fi rst evidence dedicated to mathematical methods, covers of mixing in atmospheric neutrinos, and discrete symmetries, angular momentum “concepts, tools and methods”. There is a proceeds to laboratory experiments, TEKNOSERVICE is a Spanish company and rotations in space, Lorentz invariance modern angle in this chapter: as an example, and then the MSW effect, solar-neutrino and the calculation of phase-space factors, Weyl spinors are introduced and used, along oscillations and then three-fl avour with more than 25 years of experience in decay widths and cross-sections, and with the associated Lorentz transforms oscillations, concluding with the the ICT sector. It is specialized in offering concludes with a brief review of group and spin matrices. This material is better measurement of θ13. This chapter is a novel Integrated Technological Solutions, based theory. Chapter 3, on accelerators, includes absorbed by graduate students. The rest of and useful addition to the textbook. a concise yet clear description of the basic the chapter covers the traditional Klein– Chapter 12 is on the Higgs boson. It starts on the quality of TTL Professional® pro- concepts and terminology often encountered Gordon and Dirac equations, and introduces with a short introduction to spontaneous ducts and top-level service. by students starting to work on experiments the electromagnetic interaction. It concludes symmetry breaking and proceeds to a but not readily available. The topics include with a short introduction to gauge symmetry. description of the discovery of the Higgs synchronicity, beam optics, Q values Chapters 7–10 constitute a second part boson by the ATLAS and CMS experiments. Under our brand TTL Professional®, we produce and beam tunes, luminosity, and even that concentrates on particle physics. The material, with the exception of a section a wide range of computers, laptops, ultralight some characteristics of past accelerators. Chapter 7, on weak interactions, covers all on the statistical signifi cance, which is too laptops, lightweight terminals, servers, storage Chapter 4 is on particle detectors. Beyond of the material from the four-point Fermi short and ill-placed to be useful, is at the arrays and graphic workstations, all with the the standard topics expected in such an interaction to the Standard Model (SM), right level for the advanced-undergraduate- latest technology. We also create virtualization overview, e.g. the interaction of particles and although without symmetry breaking. The to-graduate student audience. radiation with matter, the chapter includes descriptions of V–A, parity violation and the The book concludes with chapter 13 software, operating systems and personalized topics that are usually neglected, including weak interactions of quarks, the CKM matrix on the LHC and BSM (physics Beyond audiovisuals solutions. Our products are constantly short presentations on signal generation, and hadron decays via the weak interaction the Standard Model). It has an interesting evolving under the supervision and monitoring triggering of experiments and the selection are clear, as is the extended introduction selection of topics, including expected ones of our Engineering and Networking laboratory, of a magnetic fi eld. As would be expected, of SU(2) × U(1) symmetry as the basis of like supersymmetry and some unexpected wich manages I+D+i projects. This department is, calorimetry is well covered, as are tracking the SM. Chapter 8, on experimental tests ones (for a textbook) like the search for new without a doubt, the cornerstone of all our detectors, to which an extensive description, of electroweak theory, is one of the more contact interactions and new resonances. projects and technological solutions. including an introduction to solid-state modern presentations of the topics covered: it The approach is quite experimental in that detectors, is included. The topics and detector starts with neutrino interactions and charged only the motivation for new phenomena is examples provided are too centred on the and neutral currents, and moves to Z physics presented, and the theory is skipped. It is LHC and its experiments, though. and then WW production at LEP. It includes nevertheless a useful introduction to the Chapter 5, on the static quark model, is some experimental aspects such as the use subject, adequate for motivating students to the fi rst “particle-physics-proper” section. of resonant depolarisation for the precise explore further. It’s a clear and self-contained introduction determination of the LEP beam energy. Overall, the book achieves its goal of to mesons and baryons, with a modern Moving away from convention, the discovery bridging the gap between undergraduate and www.teknoservice.es perspective. The authors have decided to of the W and Z bosons at the CERN SPS graduate textbooks. The descriptions of the include heavy quarks (with the exception is left for after the LEP presentation. The various topics are mostly clear, although at of the top quark) and their mesons and chapter concludes with a brief presentation of times too short. In a formal course, the tutor baryons, and the result is a full overview for the discovery of the top quark and some later would probably choose to cover the material the reader. Finally, chapter 6 on relativistic results from the Tevatron. in a slightly different mix to the order it is

quantum mechanics concludes what could Chapter 9, on dynamic quarks, breaks presented here, combining material from the▲ be called the fi rst part of the book on the fl ow slightly. It contains Rutherford fi rst part (chapters 2–6) and the second

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CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017 CERN Courier January/February 2017 Bookshelf Bookshelf Silicon Drift Detectors • Solid State Design • Easy to Use part (mainly chapters 7–10). In summary, motion that describe the positions of the energy levels, and continues with a evolved during the past 50 years. In particular, • Low Cost this is a welcome, useful and modern various parts of a system as functions of discussion of coherence effects effects (of he dedicates various chapters to the addition to the current list of textbooks in time using standard analytic functions. If, fi rst-, second- and third-order). connections of string theory with quantum particle physics. on one side, the formulations of mechanics Finally, a section is dedicated to selected fi eld theory, mathematics, cosmology, FAST SDD® ● Paraskevas Sphicas, CERN, and University of of Lagrange and Hamilton lead to systems examples from recent research topics particle physics and quantum gravity. Athens, Greece. that cannot be solved in the usual sense of in which the use of the density matrix The last part of the book discusses the Count Rate = >1,000,000 CPS the word, perturbation theory, in turn, fails is profi table, including laser tweezers, social aspects of science: the diverse ways Tutorials in Radiotherapy Physics: in providing approximate solutions because laser cooling, coherent population of approaching the topic as well as various Resolution Peaking Time Advanced Topics with Problems of the problem of small dividers. This is trapping and transfer, optical magnetism, personal driving forces. A chapter is also 125 eV FWHM 4 µs and Solutions the path that led originally to the discovery electromagnetically induced transparency, dedicated to the most signifi cant criticisms 130 eV FWHM 1 µs By Patrick N McDermott of chaos, and it is the one that the author squeezed light and quantum information of string theory, to which the author 140 eV FWHM 0.2 µs CRC Press pursues in the book. processing. provides a reply. 160 eV FWHM 0.05 µs This book addresses fi ve selected physics The fi rst part is dedicated to the basic The text is based on two decades of The book is intended to appeal to topics in modern cancer radiation therapy. concepts of the Lagrangian and Hamiltonian lectures and is oriented to graduate students laypersons interested in fundamental Examining them in more detail than can formulation of mechanics, and to canonical not only of traditional disciplines such as physics as well as to physics students, so 5.9 SDD Spectrum keV be found in standard medical-physics transformations. The author then deals with physics, chemistry, electrical engineering the author chooses to avoid mathematical 55 textbooks, the author has also formulated more advanced topics, including Liouville’s and materials science, but also of formulations of the theory. However, the Fe and solved a large number of exercises that theorem and perturbation theory. In the interdisciplinary courses such as biophysics, risk is that the book is then not suffi ciently eV FWHM Counts 125 are provided at the end of each chapter, third part of the book, the modern theory of biomedicine and photochemistry. clear and explanatory to be an easy read 25 mm2 x 500 µm 11.2 µs peaking time 6.4 together with a detailed bibliography. chaos is introduced. The author describes In this second revised edition, new for non-experts, nor technical and detailed keV Despite its title, the book is not a chaotic motion using the tools of discrete sections on quantum interference, Fano enough to appeal to students. P/B Ratio: 20000/1 Energy (keV) substitute for comprehensive textbooks maps and Poincaré sections, along with resonances, optical magnetism, quantum Exactly Solvable Models in Many-Body in medical-radiation physics, rather it the Poincaré–Birkhoff and Kolmogorov– computation, laser cooling of solids, and Resolution vs Peaking Time Theory 180 complements them. It is therefore of interest Arnold–Moser (KAM) theorems and their irreducible representation of magnetic 2 By N H March and G G N Angilella 25 mm to experienced medical physicists who The last theme, tumour control and normal applications. interactions have been included, along with 170 would like to better understand the physics tissue complications, is the most relevant for Each chapter is accompanied by a set of more than 40 new problems. World Scientifi c of their daily work, as well as to young the patient. Is the therapy effective? What problems, with the last section providing Following their previous book 160 Standard SDD Why String Theory? researchers approaching this discipline is the quality of life after treatment? The more advanced projects that require some on many-body theory, the ® for the fi rst time, often following a PhD in answers to these questions may be searched expertise in computing. As a conclusion, By Joseph Conlon authors have written a new 150 FAST SDD particle physics. for using the bridge that connects physics to an appendix discusses the relevance of the CRC Press volume focused on exactly 140 The fi rst section deals with the main medicine. To accomplish this task, models KAM theorem to the ergodic hypothesis and As the author himself states, solvable models, to add to the tool of modern cancer radiation therapy: are necessary. Starting from the concepts of the second law of thermodynamics. the primary aim of this book literature in this fi eld. Several 130 Resolution (eV FWHM @ 5.9 keV)

the electron linear accelerator (linac). probability and of dose-volume histograms, is to explain why so many theoretical models are presented for selected 120 Lectures on Light: Nonlinear and Quantum 0 1 2 3 4 5 Starting from the basics of electrodynamics, empirical and mechanistic models are scientists choose to work on systems in condensed states of matter – Peaking Time (μs) travelling- and standing-wave linear presented together with the serial and parallel Optics using the Density Matrix (2nd a theory that has no direct including solid, liquid and disordered states accelerators are discussed together with architecture of the organs in the human body. edition) experimental support and is – and for systems of few or many bodies. Throughput resonating cavities. Particular care is given The application of radiation physics to By Stephen C Rand unlikely to have so anytime soon. The book starts with an introduction to 1,00,0000 Oxford University Press to mathematical formulations and to the medicine is an expanding multidisciplinary String theory, the origins of which date low-order density matrices, then discusses 0.2 μs defi nition of symbols. This chapter could fi eld based on knowledge, tools and The aim of this book is to back to 1968, has developed into a major exactly or nearly exactly solvable models for also appeal to accelerator physicists willing techniques derived from nuclear and particle bridge the gap between component of theoretical particle physics. several few-particle systems. The material 100,000 1 μs to know more about electron acceleration at physics. This book will therefore appeal introductory quantum It is most famous as a theory of quantum is arranged according to the statistics of energies of a few MeV. not only to curious medical physicists and mechanics and the most recent gravity and as a candidate unifi ed theory these particle assemblies, going from small 4 μs Proton therapy, which is generally scientists active in the fi eld, but also to advances in modern optics. of fundamental interactions at the smallest clusters of fermions to small clusters of 10,000

considered an advanced topic in medical physicists in general who – as the author The author opts for an scales – so small that, unfortunately, we bosons – with specifi c reference to Efi mov Rate (OCR) Output Count radiation therapy, is approached in a comments – “like understanding”. unconventional approach. Rather than cannot directly test it with experiments. trimers in nuclear and condensed-matter somewhat easier way. Starting from an ● Saverio Braccini, AEC-LHEP, University of Bern, providing an exhaustive treatment, he Although string theory is built on assemblies – to anyon statistics. 1,000 1,000 10,000 100,000 1,000,0000 historical introduction, emphasis is given Switzerland. introduces a single analytic tool – the a very solid mathematical basis and The second group of chapters is Input Count Rate (ICR) to accelerators and to dose-distribution density matrix – to analyse complex optical allows rigorous calculations, the author dedicated to models for selected systems, with a glimpse of future Books received phenomena and applies it to a wide range of uses almost no equations. Rather than a many-body systems in condensed matter, developments. It is a pity that carbon-ion problems. Among the many mathematical textbook, this is a book on the history, where particular attention is given to therapy is not mentioned and that active Lectures in Nonlinear Mechanics and tools available to treat nonlinear and science and philosophy lying behind a superconductivity and superfl uidity, and to dose-distribution systems are not discussed Chaos Theory quantum optics, he chooses the density fascinating and speculative theory. isolated impurities in a solid. Pair-potential in more detail. By Albert W Stetz matrix because it is extremely versatile In the fi rst part, the theory of and many-body force models for liquids are The two topics that follow address World Scientifi c and applicable virtually to any problem. quantum-mechanical relativistic strings also discussed, as well as disorder and its the daily work of the medical physicist. This concise book provides a In particular, it is well suited for dealing is placed within the broader context of implications for transport in solids. Dose-computation algorithms are treated rigorous introduction to the with coherence in isolated or interactive theoretical particle physics, and ultimately The authors then deal with more general following a careful mathematical formulation theory of nonlinear mechanics systems, and allows researchers to ignore science in general. It is then discussed why topics, in particular statistical fi eld theory Please see our web site for complete complemented by examples and references and chaos, suitable for students parts of a problem that appear irrelevant. there is still a need for ideas and paradigms (discussing some specifi c models and specifications and vacuum applications to practical cases. Deterministic radiation across physics, mathematics and After covering the basics, the book that go beyond what we already know, and critical exponents) and relativistic fi eld transport is introduced, starting from the engineering. quickly passes to more sophisticated why string theory is a candidate for being theory. Open problems in quantum gravity basic quantities used in medical radiation Nonlinear dynamics treats problems topics. It starts with the simplest systems a global theory that includes all others. are also briefl y reviewed in the concluding ® AMPTEK Inc. physics. The transport and Fermi–Eyges that cannot be “solved”, in the sense that (stationary two-level atoms) and then Following this, the author describes the chapter, and several appendices are included [email protected] equations are then derived and discussed. it is not possible to derive equations of introduces atomic motion and additional motivation driving this fi eld and how this has at the end of the book. www.amptek.com

64 65

CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERN Courier January/February 2017  CERN Courier Archive: 1974   A LOOK BACK TO CERN C OURIER VOL . 14, F EBRUARY 1974, COMPILED BY P EGGIE R IMMER  n E W s new Mpod version 2

All the world’s a hadron • New very compact design , cooling from side to

SLAC Frascati side Following the coming into operation of the 6 GeV Bevatron at Berkeley in February • Removable fan unit including air filter

1954, the particle population explosion • Mpod Mini crate for 4 LV or HV modules defi ed understanding. Then came a beautiful application of unitary symmetry theory, • LV and HV modules freely combinable

which grouped particles in an orderly way • MPOD-Controller with Ethernet, CAN-bus, USB with well-defi ned relationships between • Web-ready + SNMP, OPC server , EPICS them. Noting an absent member in one of these groups, the omega minus was predicted • Low Voltage: 8 channels 0..8V to 0..120V and, in February 1964, Brookhaven range, identifi ed this particle, crowning one of the The detection system surrounding a beam The ADONE storage ring at Frascati, where great achievements of high-energy physics. collision region at SPEAR, used in gathering combined electron–positron energies of up low noise (<2mVpp 20MHz) The famous quark hypothesis is one the new astonishing results on hadron to 3 GeV had already indicated that the attempt to explain the particle grouping and production. hadron-production cross-section was high. relationships. It postulates three types of

fractionally charged particles [up, down and covered at the electron–positron storage ring measurements can be explained by no quark strange] coming together in different ways to [SPEAR] at Stanford. Experiments there model, no matter how coloured. They show WIENER Mpod LV parallel module build up the multitude of discovered hadrons have resoundingly confi rmed the Cambridge the ratio rising with increasing energy and by (which respond to the strong interaction). measurements and completely overthrown 5 GeV it has reached a value of about 6. • Mpod module with 4 low voltage DC channels, up However, quarks have never been isolated our understanding of what is going on. The results can also be applied to 120V and 100W/channel The total cross-section for the production subversively to another revered concept – as separate entities despite a multitude of combinable with 50W channels for example searches, and some results do not line up of hadrons is about 25 nb and is virtually scaling. Scaling makes it possible to predict 2x100W and 4x50W output channels/module precisely with predictions. constant over energies up to 5 GeV. This is in the energy distribution of the hadrons at The past 10 years have seen no let-up in complete contradiction to the prediction of the any energy once they have been measured • lowest noise and ripple <3mVPP, high stability the accumulation of fresh information. This quark model, which says that the cross-section at another energy. It has worked beautifully 0,2%/10k ; voltage or current controlled

has been particularly true of recent years should fall off as the square of the energy. in studies of lepton–hadron interactions, for operation , 0,5mA/0,5mV resolution when the opening up of new energy ranges The quark model gets another jolt when example the elastic scattering of electrons off has produced fascinating results. The 76 GeV the total cross-section for producing hadrons nucleons. Why then does scaling not apply • all channels are individually controlled, floating proton synchrotron at Serpukhov, the CERN is compared with that for producing pairs for electron–positron collisions? and sensed programmable trip points, ramps, Intersecting Storage Rings [ISR], and the of muons. The simple quark model says the It is also intriguing that the hadron failure action and group behavior 400 GeV proton synchrotron at NAL Batavia ratio should be constant at 2/3, independent energy distribution from electron–positron have all contributed something new. Fresh of energy. ADONE results had already upset collisions looks like that in very high energy surprises from experiments on electron– the apple cart but they were still compatible proton collisions, such as pion production positron storage rings were reported by with a more complicated variant of the data at 90° in the centre of mass at NAL and B Richter (SLAC) at the American Physical quark model involving “coloured” quarks the ISR. It is as if the electron is sensitive to Society Meeting in Chicago, 4–7 February. (introducing a property for the quarks like an the strong interaction within a tiny radius of The high-energy collision of an electron ultra-strangeness). The coloured variant still 10 –16 cm. So, is even the best-known lepton VME 475 Mini and a positron brings matter and antimatter insisted on a constant value for the ratio, this really a hadron at heart? • 7 slot monolithic backplane together, resulting in annihilation into time of 2. But the Cambridge and SPEAR ● Compiled from texts on pp39–42. energy. This energy (photons) can convert VME/VME64, cPCI/PXI backplane, 250 into hadrons (predominantly pions). Thus or 500W total power hadrons emerge from lepton collisions. Compiler’s Note • Very compact design, variable cooling The fi rst inkling that things were going In 1964, Gell-Mann and Zweig proposed a quark model of hadrons, adrift came from experiments at the purely for bookkeeping purposes. But increasing accelerator energies options (front to rear, side to side) electron–positron storage ring ADONE brought growing evidence that the hypothetical up, down and strange • WIENER CML Shelf Manager for local at Frascati. Measurements indicated the quarks were in fact real and point-like. For example, particles with high and remote monitoring and control, hadron-production cross-section up to 3 GeV transverse momentum were emerging from proton–proton collisions at centre-of-mass energy is over twice that monitors and controls power supply, fan, the ISR, reminiscent of the large-angle scattering of alpha particles that expected. A few measurements with electrons remote on/off, SYSRES, thermal and positrons at energies up to 5 GeV centre led to Rutherford’s discovery of the atomic nucleus. The GIM mechanism, monitoring, user I/O programming, with proposed by Glashow, Iliopoulos and Maiani in 1970, required the of mass then came from the Cambridge Ethernet (SNMP V3) and USB interface bypass. They were very much higher than existence of a fourth, heavier quark, and by the end of 1974 it had been predictions, but the accelerator was closed identifi ed, by Richter at SLAC and Ting at BNL, in the charm/anticharm down before they could be checked. In recent J/ψ meson. And with real quarks, there was no need for hadronic leptons. W-IE-NE-R, Plein & Baus GmbH – Linde 18, D51399 Burscheid (Germany) months the same energy range has been Fon:+49 2174 6780 – FAX: +49 2174 678 55 Web: www.wiener-d.com 66

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Marzo.indd 1 23/12/16 15:35 CERNCOURIER www. V o l u m e 5 7 N u m b e r 1 J a n u ary /F e b r u a r y 2 0 1 7 CERNCOURIER V o l u m e 5 7 N u m b e r 1 J a n u a r y /F e b r u a r y 2 0 1 7 Contents

5 V i ew p o i n t F e at u r e s 39 Does antimatter fall up? 16 The dawn of a new era CERN experiments to test the free-fall of antiatoms. 7 N ew s Gravitational waves open a profound new vista on nature. 41 The many lives of supergravity India to become associate Member State Slovenia to become • • 40 years at the forefront of attempts to unify nature’s forces. associate Member State in pre-stage to membership • Antihydrogen 21 General relativity at 100 atoms show their colour • AWAKE makes waves • Proton–lead Testing Einstein’s masterpiece with ever increasing precision. 45 Linking waves to particles run tops record year of LHC operations • ATLAS makes precision 27 Gravity’s quantum side Gravitational waves could also shed light on the microscopic world. measurement of W mass Run 2 promises a harvest of beauty • Quantum gravity continues to confound theorists. for LHCb • ALICE zeroes in on cold-matter effects • Protons 49 F a ce s & P l a ce s probe quark–gluon plasma at CMS Electron gun shrunk to 31 The LHC’s extra dimension • 58 R ec r u i t me n t matchbox size Searches at ATLAS and CMS constrain models of extra dimensions. 63 oo k s h elf 13 S c i e n cewat c h 34 Catching a gravitational wave B The technology behind LIGO’s epochal discovery. 15 A s t r owat c h 66 A r c h i ve

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