CERN Courier January/February 2017 All new smart News

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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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.

8 9

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

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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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 cern[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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