Vol57-Issue6-P007-E.Pdf

CERN Courier July/August 2017 News

I nternatIonal Lithuania joins CERN as associate member

On 27 June, representatives of CERN and the CERN Director-General, Fabiola Gianotti, Republic of Lithuania signed an agreement in president of Lithuania, Dalia Grybauskaitė, the capital city of Vilnius admitting Lithuania R D a cˇ k u s and Lithuanian minister of foreign affairs, as an associate Member State. The agreement Linas Antanas Linkevičius, at the signing of will enter into force once official approval is the agreement in Vilnius. received from the Lithuanian government. “The involvement of Lithuanian scientists role in developing databases for the at CERN has been growing steadily over the experiment. The country actively promoted past decade, and associate membership can the BalticGrid in 2005, and more generally now serve as a catalyst to further strengthen participates in detector development relevant particle physics and fundamental research in to the High Luminosity LHC. the country,” said CERNʼs Director-General, Lithuania’s associate membership will Fabiola Gianotti. “We warmly welcome strengthen the long-term partnership Lithuania to the CERN family, and look between CERN and the Lithuanian scientific forward to enhancing our partnership community. It will allow Lithuania to take in science, technology development and part in meetings of CERN Council and its education and training.” committees, and Lithuanian scientists will Lithuania’s relationship with CERN and scientific institutions in high-energy be eligible for staff appointments. Finally, dates back to a co-operation agreement physics experiments at CERN. Lithuania once the agreement enters into force, signed in 2004, which paved the way to has been a long-time contributor to the CMS Lithuanian industry will be entitled to bid for participation of Lithuanian universities experiment and has also played an important CERN contracts. l H C n e w s Sommaire en français Physics resumes at LHC 1.6

) La Lituanie devient État membre associé 7 Run 1 Long Run 2 –1

s Shutdown 1 du CERN –2 First stable beams in the LHC were declared 1.2 La physique reprend au LHC 7 on 23 May, just 25 days after the first beam cm 34 LHCb découvre un nouveau baryon 8 was injected and almost three weeks 0.8 ahead of schedule. Since then, interleaved CMS scrute la production de paires de 8 with physics operation and remaining bosons W de même signe commissioning activities, the LHC teams 0.4 have been busy ramping up the intensity ATLAS enquête sur le boson de Higgs à 9

of the beams. During this procedure, the peak luminosity (10 0 13 TeV 2011 2012 2013 2014 2015 2016 2017 number of proton bunches circulating the ALICE se penche sur l’évolution du plasma 10 machine is increased in a stepwise manner: quarks-gluons beginning with three bunches per beam and LHC Run 2 has seen a record increase in going up to 12, 72, 300, 600, 900, 1200, 1800, peak luminosity. Le détecteur XENON1T fournit ses 10 2400 and finally 2556 bunches per beam. To premières données ensure that all systems work as they should, the walls and destabilising the beam. Such Premiers faisceaux pour l’expérience 11 each step requires a minimum of 20 hours of “electron-cloud” effects can be reduced Muon g-2 stable-beam operation and that the machine by repeatedly filling the LHC with closely is filled three times. As theCourier went spaced bunches, provoking intense electron L’ESA donne le feu vert à LISA 11 to press on 28 June, 2556 bunches were clouds that gradually become less prone to L’amélioration de la luminosité du LHC circulating in the machine and already the produce further electrons. s’accélère 12 experiments had clocked an integrated The rapid and smooth restart of the LHC luminosity of around 5 fb–1. this year, which marks the continuation of Des détecteurs de neutrinos en voyage 12 Another important procedure during the Run 2 at a centre-of-mass energy of 13 TeV, L’aube de l’humanité repoussée plus loin 15 LHC restart is the so-called scrubbing run to is due to the excellent availability of the dans le passé condition the vacuum chamber, which took machine and its injector chain, and also the place in early June. Despite the ultra-high dedication of many specialists. The LHC is Des astronomes rapportent la première 17 vacuum of the LHC beam pipe, residual gas now ready to continue the intensity ramp for observation d’une supernova manquée molecules and electrons remain trapped on physics-data collection, with the ambitious the walls of the chamber and can be liberated goal of reaching an integrated luminosity of by the circulating beam, eventually heating 45 fb–1 for 2017.

CCJulAug17_News.indd 7 28/06/2017 16:28 CERNCOURIER www. V o l u m e 5 7 N u m b e r 6 J u l y /A u g u s t 2 0 1 7 CERN Courier July/August 2017 CERN Courier July/August 2017 News News

L H C experiments observation of the electroweak production of 35.9 fb–1 (13 TeV) VBF H±± → W±W± 35.9 fb–1 (13 TeV) same-sign W-boson pairs in proton–proton

collisions, with an observed significance data mH±± = 200 GeV CMS 300 observed CMS EW WW ±± LHCb discovers new baryon of 5.5 standard deviations. The result mH = 600 GeV preliminary ) (fb) preliminary 150 ± median expected WZ W

does not point to physics beyond the SM: non-prompt bkg. unc. ± expected ±1␴

W ␴ The LHCb collaboration + a cross-section of 3.8±0.7 fb is measured others expected ± 2

2 ++ 400 Ξcc → 800 dcc Ξcc 200 has discovered a new data RS ucc within the defined fiducial signal region, ±± 2 600 scc 100 weakly decaying particle: a data WS + corresponding to 90±22% of the result 400 Ω ++ 300 data SB cc events baryon called the Ξ , which + + expected. An excess of events could have been ) × B(H cc 200 0 , cand. per 3 MeV/c Λ Σ cc ±± contains two charm quarks and an up quark. Σc ++ caused by the presence of a doubly charged 100

ddc (H 2250 2300 2350 udc uuc Σc 50 200 – + 2 The discovery of the new particle, which was M(pK π ) (MeV/c ) usc Higgs boson that couples to W bosons, and the VBF + – + + dsc 0 ␴ observed decaying to the final-stateΛ c K π π 0 Ωc + analysis sets upper bounds on the product of Ξc ssc Ξc and is predicted by the Standard Model, was 100 the cross-section and branching fraction for n p 0 0 presented at the European Physical Society udd uud such particles (figure, right). Bounds on the candidates per 10 MeV/c LHCb 2016 – uds 500 1000 1500 2000 200 400 600 800 1000 conference in Venice on 6 July. Σ dds 0 structure of quartic vector-boson interactions 0 Λ, Σ uus Σ+ mjj (GeV) mjj (GeV) Although the quark model of hadrons 3300 3500 3700 dss uss are also obtained in the framework of predicts the existence of doubly heavy ++ 2 – 0 dimension-eight effective field theory (Left) Distribution of the dijet mass in the signal region, with hatched bars including M(Ξcc ) (MeV/c ) Ξ Ξ baryons – three-quark states that contain operators, and the measurements set 95% statistical and systematic uncertainties. Predictions for two scenarios of doubly charged two heavy (c or b) quarks – this is the first (Left) Mass spectrum recorded in 2016 showing the right-sign (RS) signal sample confidence-level limits that are up to six times Higgs boson production (red and green) are also shown. (Right) Expected and observed ++ + – + + + – + + time that such states have been observed Ξcc → Λc K π π along with two control samples: sideband (SB) Λc K π π candidates, and more stringent than previous results. 95% confidence-level upper limits on the product of cross-section and branching fraction + – + – unambiguously with overwhelming statistical wrong-sign (WS) Λc K π π candidates, each normalised to have the same area as the RS This first observation of the purely for doubly charged Higgs boson decays to a same-sign W-boson pair. + significance (well in excess of 5σ with respect sample. The inset shows the Λc mass distributions with the signal (cross-hatch) and sideband electroweak production of same-sign to background expectations). The properties (vertical lines) regions. (Right) An illustration of the spin-1/2 baryon multiplet including light W-boson pairs is an important milestone demonstrate that the High Luminosity LHC, ● Further reading ++ ++ of the newly discovered Ξcc baryon shed quarks and the charm quark, with the Ξcc located on the top floor. towards precision tests of VBS at the LHC, due to enter operation in the early 2020s, CMS Collaboration 2017 CMS-PAS-SMP-17-004. light on a long-standing puzzle surrounding and there is much more to be learned from should even allow a direct investigation of CMS Collaboration 2017 CMS-PAS-HIG-16-027. + the experimental status of doubly charmed eliminates all promptly decaying particles, for the Ξcc. Despite SELEXʼs confirmation the rapidly growing data sets. Studies longitudinal W-boson scattering. CMS Collaboration 2017 CMS-PAS-SMP-14-008. baryons, opening an exciting new branch of leaving only long-lived ones that are the of the observation in a second decay mode, investigation for LHCb. hallmark of weak transitions. all subsequent searches – including efforts at ATLAS probes Higgs ATLAS preliminary data ATLAS preliminary data The team scrutinised large high-purity Although the existence of baryons the FOCUS, BaBar and Belle experiments 50 H → ZZ*→ 4l signal (mH = 125 GeV) H → ZZ*→ 4l syst. uncertainties + – + 13 TeV, 36.1 fb–1 background ZZ* 0.12 13 TeV, 36.1 fb–1 HRes k = 1.1, +XH samples of Λc → p K π decays in LHC with valence-quark content ccu and ccd – failed to find evidence for doubly charmed ++ boson at 13 TeV background tt + V, VVV NNLOPS k = 1.1, +XH data recorded at 8 and 13 TeV in 2012 (corresponding to the Ξcc and its isospin baryons. That left both theorists and 40 background Z+jets, tt MG5 FxFx k = 1.47, +XH (fb/GeV) 0.08 + uncertainty XH = VBF+WH+ZH+ttH+bbH

and 2016, respectively, and discovered an partner Ξcc) is expected, the experimental experimentalists awaiting a firm observation T,4l p-value NNLOPS = 25% + – + + isolated narrow structure in the Λc K π π status of these states has been controversial. In by a more powerful heavy-flavour detector The ATLAS 30 p-value MG5 FxFx = 42% + 0.04 p-value HRes = 21%

mass spectrum (associating the Λc baryon 2002, the SELEX collaboration at Fermilab such as LHCb. Although the new result from collaboration has d ␴ /dp 20 with further particles) at a mass of around in the US claimed the first observation LHCb does not fully resolve the puzzle (with released new results 0 2 2 events/2.5 GeV 3620 MeV/c . After eliminating all known of this class of particle by observing a a mass difference of 103±2 MeV/c , LHCbʼs on measurements p ++ + 10 2 potential artificial sources, the collaboration significant peak of about 16 events at a mass of Ξcc and SELEXʼs Ξ cc seem irreconcilable as of the properties of the Higgs boson using 2 + – + 1 concluded that the highly significant peak is 3519±1 MeV/c in the Λc K π mass spectrum, isospin partners), the discovery is a crucial the full LHC proton–proton collision data 0 data/theory a previously unobserved state. Corroboration which they identified as the closely related step to an empirical understanding of the set collected at a centre-of-mass energy of ++ + 80 100 120 140 160 0 10 15 20 30 45 60 80 120 200 350 that it is the weakly decaying Ξcc came from state Ξcc. Puzzlingly, the short lifetime (which nature of doubly heavy baryons. 13 TeV in 2015 and 2016, corresponding to an m (GeV) p (GeV) examining a subset of data in which the was too small to be measured at SELEX) integrated luminosity of 36.1 fb–1. 4l T,4l reconstructed baryons lived for a measurable and the very large production rate of the state ● Further reading One of the most sensitive measurement (Left) The invariant mass spectrum measured in the four-lepton final state with the expected period before decaying. Such a requirement seemed not to match theoretical expectations LHCb Collaboration 2017 LHCb-PAPER-2017-018. channels involves Higgs boson decays via SM background and signal superimposed. (Right) The measured differential cross-section for two Z bosons to four leptons (two pairs of the transverse momentum (pT,4l) of the Higgs boson, compared to theoretical predictions. oppositely charged electrons or muons). CMS observes production of same-sign W-boson pairs Although only occurring in about one in four-lepton events were measured with a fit to mechanisms. By measuring the number and every 8000 Higgs decays, it gives the cleanest the invariant mass distribution, allowing the properties of jets produced in these events, The LHC was built with to the way Higgs and vector bosons couple to at an energy of 8 TeV, but were insufficient signature of all the Higgs decay modes. inclusive cross-section to be measured with Higgs boson production via the fusion of two a guaranteed discovery: one another and to the Higgs boson’s mass, to claim an observation. The new study is Using this channel, ATLAS measured both an accuracy of about 16%. gluons was studied. The measured inclusive the ATLAS and CMS models of physics beyond the SM predict based on 36 fb–1 of data collected in 2016 at the inclusive and differential cross-sections Candidate Higgs boson events were and differential cross-sections were found experiments would either enhancements to VBS via modifications 13 TeV. Events were selected by requiring they for Higgs boson production. Although these corrected for detector measurement to be in agreement with the Standard Model find a Higgs boson, or it to the Higgs sector or from the presence of contain two leptons (electrons or muons) with have been measured before at lower LHC effects and classified according to their (SM) predictions. The results were used to would discover new physics in vector boson additional resonances. the same electric charge, moderate missing collision energy, the increased integrated kinematic properties to measure differential constrain possible anomalous Higgs boson scattering (VBS) at high energies. The A recent analysis by CMS aimed to identify transverse momentum, and two jets with a luminosity and larger cross-section production cross-sections. Among these, interactions with SM particles. discovery of a Higgs-like boson in July 2012 events in which a W-boson pair is produced large rapidity separation and a large dijet compared to LHC Run 1 allows their the measurement of the momentum of the confirmed that the W and Z bosons acquire purely via the electroweak interaction. mass. About 67 signal events were expected, magnitudes to be determined with increased Higgs boson transverse to the beam axis ● Further reading mass through the Higgs mechanism, but to Requiring events to have a same-sign with the dominant sources of background precision. In total, around 70 Higgs boson to probes different Higgs boson production ATLAS Collaboration 2017 ATLAS-CONF-2017-032. determine whether the observed particle W-boson pair reduces the probability of events coming from top quark–antiquark corresponds to the single Higgs boson production via the strong interaction, making pairs and WZ boson pairs. The event yield of expected in the Standard Model (SM), it is it an ideal signature for VBS studies. The the signal process is then extracted using a 2D Les physiciens des particules du monde entier sont invités à apporter leurs CERN Courier welcomes contributions from the international now paramount to precisely measure the first experimental results on this final state fit of the dijet and dilepton mass distributions contributions au CERN Courier, en français ou en anglais. Les articles retenus particle-physics community. These can be written in English or French, Higgs boson’s contributions to VBS. Since were reported by ATLAS and CMS based (figure, left). 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 the behaviour of VBS amplitudes is sensitive on 20 fb–1 of LHC data collected in 2012 The new CMS study provides the first 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].

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CCJulAug17_News.indd 8 28/06/2017 16:28 CCJulAug17_News.indd 9 28/06/2017 16:29 CERNCOURIER www. V o l u m e 5 7 N u m b e r 6 J u l y /A u g u s t 2 0 1 7 CERN Courier July/August 2017 CERN Courier July/August 2017 News News

L H C experiments observation of the electroweak production of 35.9 fb–1 (13 TeV) VBF H±± → W±W± 35.9 fb–1 (13 TeV) same-sign W-boson pairs in proton–proton

does not point to physics beyond the SM: non-prompt bkg. unc. ± expected ±1␴

W ␴ The LHCb collaboration + a cross-section of 3.8±0.7 fb is measured others expected ± 2

mass spectrum (associating the Λc baryon 2002, the SELEX collaboration at Fermilab such as LHCb. Although the new result from collaboration has d ␴ /dp 20 with further particles) at a mass of around in the US claimed the first observation LHCb does not fully resolve the puzzle (with released new results 0 2 2 events/2.5 GeV 3620 MeV/c . After eliminating all known of this class of particle by observing a a mass difference of 103±2 MeV/c , LHCbʼs on measurements p ++ + 10 2 potential artificial sources, the collaboration significant peak of about 16 events at a mass of Ξcc and SELEXʼs Ξ cc seem irreconcilable as of the properties of the Higgs boson using 2 + – + 1 concluded that the highly significant peak is 3519±1 MeV/c in the Λc K π mass spectrum, isospin partners), the discovery is a crucial the full LHC proton–proton collision data 0 data/theory a previously unobserved state. Corroboration which they identified as the closely related step to an empirical understanding of the set collected at a centre-of-mass energy of ++ + 80 100 120 140 160 0 10 15 20 30 45 60 80 120 200 350 that it is the weakly decaying Ξcc came from state Ξcc. Puzzlingly, the short lifetime (which nature of doubly heavy baryons. 13 TeV in 2015 and 2016, corresponding to an m (GeV) p (GeV) examining a subset of data in which the was too small to be measured at SELEX) integrated luminosity of 36.1 fb–1. 4l T,4l reconstructed baryons lived for a measurable and the very large production rate of the state ● Further reading One of the most sensitive measurement (Left) The invariant mass spectrum measured in the four-lepton final state with the expected period before decaying. Such a requirement seemed not to match theoretical expectations LHCb Collaboration 2017 LHCb-PAPER-2017-018. channels involves Higgs boson decays via SM background and signal superimposed. (Right) The measured differential cross-section for two Z bosons to four leptons (two pairs of the transverse momentum (pT,4l) of the Higgs boson, compared to theoretical predictions. oppositely charged electrons or muons). CMS observes production of same-sign W-boson pairs Although only occurring in about one in four-lepton events were measured with a fit to mechanisms. By measuring the number and every 8000 Higgs decays, it gives the cleanest the invariant mass distribution, allowing the properties of jets produced in these events, The LHC was built with to the way Higgs and vector bosons couple to at an energy of 8 TeV, but were insufficient signature of all the Higgs decay modes. inclusive cross-section to be measured with Higgs boson production via the fusion of two a guaranteed discovery: one another and to the Higgs boson’s mass, to claim an observation. The new study is Using this channel, ATLAS measured both an accuracy of about 16%. gluons was studied. The measured inclusive the ATLAS and CMS models of physics beyond the SM predict based on 36 fb–1 of data collected in 2016 at the inclusive and differential cross-sections Candidate Higgs boson events were and differential cross-sections were found experiments would either enhancements to VBS via modifications 13 TeV. Events were selected by requiring they for Higgs boson production. Although these corrected for detector measurement to be in agreement with the Standard Model find a Higgs boson, or it to the Higgs sector or from the presence of contain two leptons (electrons or muons) with have been measured before at lower LHC effects and classified according to their (SM) predictions. The results were used to would discover new physics in vector boson additional resonances. the same electric charge, moderate missing collision energy, the increased integrated kinematic properties to measure differential constrain possible anomalous Higgs boson scattering (VBS) at high energies. The A recent analysis by CMS aimed to identify transverse momentum, and two jets with a luminosity and larger cross-section production cross-sections. Among these, interactions with SM particles. discovery of a Higgs-like boson in July 2012 events in which a W-boson pair is produced large rapidity separation and a large dijet compared to LHC Run 1 allows their the measurement of the momentum of the confirmed that the W and Z bosons acquire purely via the electroweak interaction. mass. About 67 signal events were expected, magnitudes to be determined with increased Higgs boson transverse to the beam axis ● Further reading mass through the Higgs mechanism, but to Requiring events to have a same-sign with the dominant sources of background precision. In total, around 70 Higgs boson to probes different Higgs boson production ATLAS Collaboration 2017 ATLAS-CONF-2017-032. determine whether the observed particle W-boson pair reduces the probability of events coming from top quark–antiquark corresponds to the single Higgs boson production via the strong interaction, making pairs and WZ boson pairs. The event yield of expected in the Standard Model (SM), it is it an ideal signature for VBS studies. The the signal process is then extracted using a 2D Les physiciens des particules du monde entier sont invités à apporter leurs CERN Courier welcomes contributions from the international now paramount to precisely measure the first experimental results on this final state fit of the dijet and dilepton mass distributions contributions au CERN Courier, en français ou en anglais. Les articles retenus particle-physics community. These can be written in English or French, Higgs boson’s contributions to VBS. Since were reported by ATLAS and CMS based (figure, left). 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 the behaviour of VBS amplitudes is sensitive on 20 fb–1 of LHC data collected in 2012 The new CMS study provides the first faites part de vos suggestions à la rédaction à l’adresse [email protected]. an article, please send proposals to the editor at [email protected].

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M u o n M a G n e t i c M o M e n t ALICE zooms in on evolution of the quark–gluon plasma First beam Fermilab

The precise particle-identification pp 2.76 TeV ALICE impact-parameter collisions, the ratio is and momentum-measurement significantly less than in proton–proton 0.5 pp 7 TeV Pb–Pb 2.76 TeV at Muon g-2 capabilities of the ALICE Pb–Pb 2.76 TeV (PRC 91, 024609) collisions and models without re-scattering experiment allow researchers 0.4 effects. In contrast, no such suppression to reconstruct a variety of was observed in the φ /K– ratio. This The Muon g-2 experiment at Fermilab short-lived particles or resonances in measurement thus suggests the existence of has begun its three-year-long campaign 0.3 heavy-ion collisions. These serve as a probe K*0/K– re-scattering effects on resonances in the to measure the magnetic moment of the for in-medium effects during the last stages of last stages of heavy-ion collisions at LHC muon with unprecedented precision. On 0.2 evolution of the quark–gluon plasma (QGP). particle ratios – energies. Furthermore, the suppression of 31 May, a beam of muons was fired into the Recently, the ALICE collaboration has made φ/K K*0 yields can be used to obtain the time experiment’s 14 m-diameter storage ring, a precise measurement of the yields (number 0.1 difference between the chemical and the where powerful electromagnetic fields EPOS3 EPOS3 w/o UrQMD of particles per event) of two such resonances: thermal model, T = 156 MeV kinetic freeze-out of the system. cause the magnetic moment, or spin, of * 0 φ ch K (892) and (1020). Both have similar 0 On the other hand, at higher momenta individual muons to precess. The last time masses and the same spin, and both are neutral 0 246810 12 (pT > 8 GeV/c), these resonances were this experiment was performed, using the 1/3 strange mesons, yet their lifetimes differ by 〈dNch/dη〉 suppressed with respect to proton–proton same electromagnet at Brookhaven National a factor of 10 (4.16±0.05 fm/c for K*0, and collisions by similar amounts. The Laboratory in the late 1990s and early 46.3±0.4 fm/c for φ). Ratio of K*0 and φ yields to charged-kaon magnitude of this suppression for K*0 and 2000s, the result disagreed with predictions The electromagnet for Fermilab’s Muon g-2 experiment, which involves more than The shorter lifetime of the K*0 means that it yields at midrapidity for Pb–Pb and pp φ mesons was also found to be similar to the by more than three standard deviations. 150 scientists and engineers from nine countries. decays within the medium, enabling its decay collisions as a function of charged-particle suppression for pions, kaons, protons and This hinted at the presence of previously products (π and K) to re-scatter with other pseudorapidity density at midrapidity (dNch/ D mesons. The striking independence of this unknown particles or forces affecting the Chicago in the summer of 2013. new instrumentation to measure the muonʼs hadrons. This would be expected to inhibit dη)1/3, which is related to the final-state suppression on particle mass, baryon number muon’s properties, and motivated further Since it arrived, the Fermilab team spin-precession signal. the reconstruction of the parent K∗0, but the π freeze-out geometry of the system. Also and the quark-flavour content of the hadron measurements to check the result. reassembled the magnet and spent a year Over the next few weeks the Muon and K in the medium may also scatter into a shown are corresponding results from models puts a stringent constraint on models dealing Sixteen years later, the reincarnated Muon adjusting or “shimming” the uniformity of g-2 team will test the equipment, with K∗0 resonance state, and the interplay of these with and without re-scattering. with particle-production mechanisms, g-2 experiment will make use of Fermilab’s its field. The field created by the g-2 magnet science-quality data expected later in two competing re-scattering and regeneration fragmentation processes and parton energy intense muon beams to definitively answer is now three times more uniform than the one the year. The experiment aims to achieve processes becomes relevant for determining contrast, due to the longer lifetime of the φ loss in the QGP medium. the questions raised by the Brookhaven it created at Brookhaven. In the past year, the a precision on the anomalous magnetic the K*0 yield. The processes depend on the meson, both the re-scattering and regeneration In future, it will be important to perform experiment. It turned out to be 10 times team has worked around the clock to install moment of the muon of 0.14 parts per time interval between chemical freeze-out effects are expected to be negligible. such measurements for high-multiplicity cheaper to move the apparatus to Fermilab detectors, build a control room and prepare million, compared to around 0.54 parts per (vanishing inelastic collisions) and kinetic Using lead–lead collision data recorded events in pp collisions at the LHC. than it would have cost to build a new for first beam. The work has included: the million previously. If the inconsistency with freeze-out (vanishing elastic collisions), in at an energy of 2.76 TeV, ALICE observed machine at Brookhaven, and the large, fragile creation of a new beamline to deliver a theory remains, it could indicate that the addition to the source size and the interaction that the ratio K*0/K– decreases as a function ● Further reading superconducting magnet was transported in pure beam of muons; instrumentation to Standard Model of particle physics is in need cross-sections of the daughter hadrons. In of system size (see figure). In small ALICE Collaboration 2017 Phys. Rev. C. 95 064606. one piece from Long Island to the suburbs of measure the magnetic field; and entirely of revision.

D a r k m a t t e r G ravitational w a v e s minimum of 7.7 × 10 –47 cm2 for 35 GeV/c2 XENON1T releases WIMPs at 90% confidence level. ESA gives green light for LISA These first results demonstrate that CERN Courier first data XENON1T has the lowest low-energy On 20 June the European Space Agency ESA waves from space ( January/ background level ever achieved by a (ESA) gave the official go-ahead for the February 2017 p34). These include

Researchers from the XENON1T dark-matter R Corrieri and P De Perio dark-matter experiment, with the intrinsic Laser Interferometer Space Antenna (LISA), free-falling test masses linked by lasers experiment at Gran Sasso National background from krypton and radon reduced which will comprise a trio of satellites to and isolated from all external and internal Laboratory in Italy reported their first results to unprecedented low levels. The sensitivity detect gravitational waves in space. LISA forces except gravity. LISA Pathfinder at the 13th Patras Workshop on Axions, of XENON1T will continue to improve as is the third mission in ESA’s Cosmic Vision concluded its pioneering mission at the WIMPs and WISPs, held in Thessaloniki the experiment records data until the end plan, set to last for the next two decades, and end of June, as LISA enters a more detailed from 15–19 May (see p51). XENON1T is of 2018, when the collaboration plans to has been given a launch date of 2034. phase of study. Following ESA’s selection, the first tonne-scale detector of its kind upgrade to a larger TPC due to come online Predicted a century ago by general the design and costing of the LISA mission and is designed to search for WIMP dark The XENON1T detector and the three-storey by 2019. Several other experiments, such relativity, gravitational waves are vibrations can be completed. The project will matter by measuring nuclear recoils from building next door containing auxiliary as PANDA-X and LUX-ZEPLIN, are also of space–time that were first detected by then be proposed for “adoption” before WIMP–nucleus scattering. Continuing the equipment. competing for the first WIMP detection. the ground-based Laser Interferometer construction begins. programme of the previous XENON10 and “With our experiment working so Gravitational-Wave Observatory (LIGO) Following the first and second XENON100 detectors, the new apparatus on 34.2 live days of data acquired until beautifully, even exceeding our expectations, in September 2015. While upgrades detections of gravitational waves by LIGO contains 3200 kg of ultra-pure liquid xenon January 2017, when earthquakes in the it is really exciting to have data in hand to to LIGO and other ground-based The LISA detector will use enormous in September and December 2015, on (LXe) – 20 times more than its predecessor region temporarily suspended the run, further explore one of the most exciting observatories are planned, LISA will interferometer arms to maximise sensitivity, 1 June the collaboration announced the – in a dual-phase xenon time projection revealed the data to be consistent with the secrets we have in physics: the nature of dark access a much lower-frequency region of which is only possible in space. detection of a third event (Phys. Rev. Lett. chamber (TPC) to detect nuclear recoils. The background-only hypothesis. This allowed matter,” says XENON spokesperson Elena the gravitational-wave universe. Three 118 221101). Like the previous two, it is TPC encloses about 2000 kg of LXe, while the collaboration to derive the most stringent Aprile of Columbia University in the US. craft, separated by 2.5M km in a triangular Although highly challenging thought that “GW170104” – the signal for another 1200 kg provides additional shielding. exclusion limits on the spin-independent formation, will follow Earth in its orbit around experimentally, a LISA test mission called which arrived on Earth on 4 January – was The experiment started collecting data WIMP–nucleon interaction cross-section ● Further reading the Sun, waiting to be distorted by a fractional Pathfinder has recently demonstrated key produced when two black holes merged into in November 2016. A blind search based for WIMP masses above 10 GeV/c2, with a XENON Collaboration 2017 arXiv:1705.06655. amount by a passing gravitational wave. technologies needed to detect gravitational a larger one billions of years ago.

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M u o n M a G n e t i c M o M e n t ALICE zooms in on evolution of the quark–gluon plasma First beam Fermilab

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HL-LHC LHC luminosity upgrade accelerates Image credits: M Brice credits: Image CERN has recently implemented two important steps towards the High Luminosity LHC (HL-LHC) – an upgrade that will increase the intensity of the LHC’s collisions significantly from the early 2020s. Preparing CERN’s existing accelerator complex to cope with more intense proton beams presents several challenges, in particular concerning the system that injects protons into the LHC. At a ceremony on 9 May, a major new linear accelerator, Linac 4, was inaugurated. Replacing Linac 2, which had been in service since 1978, it is CERN’s newest accelerator acquisition since the (Left) A view of the PI-Mode Structure (PIMS) cavities, which will accelerate the Linac 4 LHC and is due to feed the accelerator beam from 100 to 160 MeV. (Right) Mauro Paoluzzi, project leader for the PSB RF overhaul, complex with higher-energy particle with one of the FINEMET cavities that will allow more intense beams. beams. After an extensive testing period, Linac 4 will be connected to the existing overhauled during that same period. At the bandwidth and means that a single cavity infrastructure during the long technical beginning of June, the first radio-frequency can cover all necessary frequency bands. shutdown in 2019/2020. cavity of the new PSB acceleration system The PSB cavity project was launched in To cope with the higher-intensity and was completed, with a further 27 under 2012 in collaboration with KEK in Japan, higher-energy beams emerging from assembly. The new cavities are based on and involved intensive testing at CERN. Linac 4, the Proton Synchrotron Booster a composite magnetic material called KEK contributed a substantial fraction (PSB), which is the second accelerator of FINEMET developed by Hitachi Metals, of the FINEMET cores and shared its the LHC injector chain, will be completely which allows them to operate with a large experience with similar technology.

C E R N N E u t R i N o P L a t f o R m Neutrino detectors Marius Julien J Ordan, and N Gonzalez on the move

On 12 June, two large detector modules for the ICARUS experiment were loaded onto trucks at CERN to begin a six-week journey to Fermilab in the US. ICARUS will form part of Fermilab’s short-baseline neutrino programme, which aims to make detailed VACUUM SOLUTIONS

measurements of neutrino interactions and E Noah search for eV-scale sterile neutrinos (CERN ICARUS (above) on its departure day, and a Courier June 2017 p25). section of Baby MIND (left) being moved to Based on advanced liquid-argon time the test-beam area. projection technology, ICARUS began its FROM A SINGLE SOURCE life under a mountain at the Gran Sasso on a smaller lorry. Baby MIND, a 75 tonne National Laboratory in Italy in 2010, prototype for a magnetised iron neutrino Pfei er Vacuum is proud to have been a supplier of innovative and customized vacuum solutions to the particle accelerator recording data from neutrino beams detector that will precisely identify community for more than 50 years. Our complete product portfolio for vacuum technology, our focus on competent and sent from CERN. Since 2014, it has been and track muons, was moved from its specialized advice supported by robust and reliable service, makes Pfei er Vacuum the partner of choice for the analytical at CERN undergoing an upgrade and construction site in building 180 to the East and research communities worldwide. refurbishment at the CERN Neutrino Hall of the Proton Synchrotron. Following Platform (CERN Courier July/August 2016 commissioning and full characterisation ■ Pumps for vacuum generation up to 10-13 hPa p21). It left CERN in two parts by road and equipped with a GPS unit that allows in the T9 test beam, at the end of July Baby ■ Vacuum measurement and analysis equipment boarded a boat on the Rhine to a port in its progress to be tracked in real time MIND will be transported to Japan to ■ Leak detectors and leak testing systems Antwerp, Belgium, where it was loaded (icarustrip.fnal.gov). be part of the WAGASCI experiment at onto a ship. As the Courier went to press, Just two days after ICARUS left CERN, JPARC, where it will contribute to a better ■ System technology and contamination management solutions ICARUS was already heading across the another key component of the CERN understanding of neutrino interactions for ■ Chambers and components Atlantic to Fermilab via the Great Lakes, Neutrino Platform was on the move, albeit the T2K experiment. Are you looking for a perfect vacuum solution? Please contact us: Pfeiffer Vacuum (Schweiz) AG · T +41 44 444 22 55 · F +41 44 444 22 66 12 [email protected] · www.pfeiffer-vacuum.com

C E R N N E u t R i N o P L a t f o R m Neutrino detectors Marius Julien J Ordan, and N Gonzalez on the move

CCJulAug17_News.indd 12 28/06/2017 16:40 17.05.05_Cern_Courier_4Prod_HiPace700_ASM340_PrismaPro_ACP15_213x282mm_EN_CH.indd 1 09.05.17 15:10 CERNCOURIER www. V o l u m e 5 7 N u m b e r 6 J u l y /A u g u s t 2 0 1 7 edwardsvacuum.com CERN Courier July/August 2017 THE WORLD BELONGS TO Sciencewatch THE nEXT GENERATION. C o m p i l e d b y J o h n S w a i n , n ortheaStern U n i v e r S i t y Advanced. Un-paralleled. There’s a new member of the nEXT family, and it’s the best yet. The nEXT85 turbomolecular pump has been developed to offer better performance, with optimised turbomolecular and drag stages, enhanced communications and a Human origins pushed back fully end user serviceable bearing. Our un-paralleled experience enables us to offer you a reliable and cost effective product that optimises performance and New remains found in a Moroccan mine A superimposition of bone fragments from achieves higher compression. could radically revise the current idea that two individuals, shown in beige and light humans originated in East Africa some blue, represents how the skulls of our earliest The Edwards nEXT85 turbomolecular pump. Advanced. Un-paralleled. 200,000 years ago. Jean-Jacques Hublin of ancestors might have looked. the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and ages determined are also consistent with colleagues analysed bones of at least five faunal and microfaunal assemblages. humans found at Jebel Irhoud, a barite mine This pushes back the origin of humans 100 km west of Marrakesh. Sharpened flint by an amazing 100,000 years, while also tools, gazelle bones and lumps of charcoal suggesting new geographical origins. were also found. These are the oldest known bones of modern humans, with an average ● Further reading age determined from thermoluminescent J-J Hublin et al. 2017 Nature 546 289. dating of 315±34 thousand years, and the D Richter et al. 2017 Nature 546 293. GR weighs a white dwarf Humans smell better Tidal phase shift measured The detection in 1919 of starlight that had According to neurobiologist John McGann been deflected by the Sun was one of the In what is arguably the first manifestation of of Rutgers University in the US, poor human first convincing proofs of Einstein’s general gravity in a quantum-mechanical system, olfaction is a 19th century myth. The idea theory of relativity. Now, Kailash Sahu physicists have observed the tidal phase shift that humans have a relatively poor sense of the Space Telescope Science Institute in an atom interferometer. Peter Asenbaum of smell, he argues, did not come from in Baltimore and colleagues have used of Stanford University and colleagues used a empirical studies of human olfaction but the Hubble Space Telescope to measure dual light-pulse rubidium atom interferometer, from a 19th century anatomist’s idea that the analogous bending of light around the in which a macroscopic spatial superposition human free will required a reduction in white-dwarf Stein 2051B, allowing them to state acts as a nonlocal probe of space–time. the brain’s olfactory bulb. In reality, our calculate its mass to be 0.675±0.051 solar Space–time curvature induces tidal forces olfactory bulbs are quite large and have masses. In addition to the first measurement on the wave function of a single quantum similar numbers of neurons to those of other of the deflection of starlight by a star other system, and the team was able to measure a mammals. In fact we are able to track odour than the Sun, the work provides valuable phase shift associated with such tidal forces. trails, and are even more sensitive than verification of the relation between the mass Additionally, the dual atom interferometer rodents and dogs to some odours. of a white dwarf and its radius. works as a gradiometer for precise gravitational measurements and could be used ● Further reading ● Further reading for measurements of the gravitational constant J McGann 2017 Science 356 597. K Sahu et al. 2017 Science 356 1046. or the gravitational Aharonov–Bohm effect. Ancient carvings and comets Solid-state refrigerators ● Further reading P Asenbaum et al. 2017 Phys. Rev. Lett. 118 183602. It has long been speculated that a comet Harmful chloroflurocarbons (CFCs) in strike caused a sudden drop in the Earth’s refrigeration devices could be replaced The team temperature during a period called the with solid refrigerants that are more measured Younger Dryas. Now, researchers at the efficient and environmentally benign. Pedro the effect of University of Edinburgh have found support Jorge von Ranke of the Universidade do the tidal for this view. They matched carvings at the Estado do Rio de Janeiro has shown that force on the Gobekli Tepe temple site in Turkey to star materials called spin-crossover systems wave asterisms, and found that the famous “Vulture have pressure-induced changes in entropy function of Stone”, dated 10,950±250 BC, fits well between low-spin and high-spin states that individual with the Younger Dryas event estimated at are large enough to use for a practical cooling particles by varying the separation 10,890 BC. The date of the strike coincides cycle. These giant “barocaloric” effects are between the two arms of the sensor with the emergence of agriculture and the analogous to magnetocaloric effects, but use interferometer (green) while keeping the beginnings of modern civilisation. pressure instead of magnetic fields. distance to the reference interferometer (pink) constant. (Image credit: APS.) ● Further reading ● Further reading M Sweatman and D Tsikritsis 2017 Mediterranean P von Ranke 2017 App. Phys. Lett. 110 181909. Archaeology and Archaeometry 17 233.

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