The CMS collaboration came to this year’s Quark Matter conference with fourteen new results, never shown before, and five other results recently submitted for publication. The majority of them exploit the high luminosity 8.16 TeV pPb, and 5.02 TeV pp and PbPb data delivered by the LHC in 2016 and 2015, respectively. Three of the analyses use the XeXe data at 5.44 TeV delivered during a 1 day run in October 2017.
The XeXe data show that the charged-particle production depends on collision geometry, not the system size. CMS continues to investigate collective effects (in which many particles in the event are correlated) in small systems, searching for the onset of these effects in events with a small multiplicity and also for similar effects in events which produce particles with relatively large mass or momentum. Significant v2 (a measure of azimuthal anisotropy) is observed in high-multiplicity pPb collisions for particles with either a single charm quark (D0) or a charm-anticharm pair (J/Psi). CMS reports also the first v3 measurement using 4-particle cumulants in pPb collisions, providing further evidence that v2 and v3 in pPb collisions are caused by initial state fluctuations.
The first measurement is reported of the detailed shapes of jets (sprays of particles created by a high momentum quark or gluon) in events with a back-to-back photon+jet pair. The results show that some of the energy in the core of the jet is redistributed to large distances from the jet axis. At the same time, the analysis of jet substructure shows that the overall distribution of particles in the core itself is hardly affected by the medium. For heavy quark studies, the first measurement of the radial profile of D mesons in jets in heavy ion collisions is reported. CMS continues to enrich its program of studying b (beauty) quarks, by adding the first measurement of Bs mesons and D mesons from the decay of beauty hadrons (called non-prompt D). For particles with charm-anticharm pairs, the measurement of Psi(2S) and J/psi mesons in PbPb, pPb, and pp collisions at 5.02 TeV reveals that the production of the Psi(2S) is suppressed with respect to J/psi in both pPb and PbPb.
The nPDFs are studied at high precision using W bosons and pairs of jets in pPb collisions at 8.16 and 5.02 TeV, respectively. The W boson results constrain the quark and antiquark nPDFs, while the dijet results represent the first evidence that the gluons which carry a large longitudinal momentum fraction in lead ions are strongly modified. The first experimental observation of the top quark in nuclear collisions is also presented. CMS reports also on the scattering of a photon from one Pb nucleus off of a photon from the other (so called light-by-light scattering) in ultraperipheral PbPb collisions.
All of the latest CMS results can be found at https://cms-results.web.cern.ch/cms-results/public-results/publications/.
All of the latest CMS heavy-ion results can be found at https://cms-results.web.cern.ch/cms-results/public-results/publications/HIN/index.html and https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/HIN/index.html
11. HIN-18-012 “Production of prompt and nonprompt J/ψ mesons in jets in pp collisions at √s = 5.02 TeV”
15. HIN-16-023 “Measurement of nuclear modification factors of Υ(1S), Υ(2S), and Υ(3S) mesons in PbPb collisions at √sNN =5.02TeV”
20. FSQ-16-012 “Measurement of light-by-light scattering in ultraperipheral PbPbcollisionsat√sNN =5.02TeV”
21. FSQ-15-009 “Femtoscopic Bose-Einstein Correlations of charged hadrons in proton-proton collisions at √s = 13 TeV“