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 NEWS 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. 7 CCJulAug17_News.indd 7 28/06/2017 16:28 CERNCOURIER www. V OLUME 5 7 N UMBER 6 J ULY /A UGUST 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 B(H ++ 300 data SB cc × events baryon called the Ξ , which + + expected. An excess of events could have been ) 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.