Exploring Nuclear Structure in Ultraperipheral Collisions

The CMS Beam Conditions and Radiation Monitoring System

Because of their large masses, the interactions of heavy quarks with the quark-gluon plasma (QGP) may be different from those of light quarks and hence can provide essential inputs in understanding the QGP. With strange quark yields being enhanced in the presence of a QGP, the production of $D_{s}^{+}$ is expected to be enhanced if recombination plays an important role in the hadronization process. Furthermore, studies of the lightest charm baryon, $\Lambda_{c}^{+}$, can provide further information to charm quark hadronization. Models involving quark coalescence predict a large enhancement of $\Lambda_{c}^{+}$ production in PbPb collisions compared to pp collisions. The $\Lambda_{c}^{+}$ and $D_{s}$ production in both pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV have been measured in the CMS experiment. Results of $\Lambda_{c}^{+}$ and $D_{s}$ differential cross-sections, and the ratios of these two yields over those for $D^{0}$ in pp and PbPb collisions are presented.

Measurements of t-channel single top quark production in proton-proton collisions at the LHC at center-of-mass energies of 7 and 8 TeV, using data collected with the CMS experiment during the years 2011 and 2012, are presented. The analyses consider final states where the W boson from the top quark decays into electron-neutrino or muon-neutrino, and makes use of kinematic characteristics of electroweak single top production for the separation of signal from backgrounds using multivariate methods. The results are compared with the most precise Standard Model theory predictions. Measurements of top/anti-top cross section ratio and of various differential single top quark production cross sections are also presented. Presented at EPS-HEP 2015 European Physical Society Conference on High Energy Physics 2015 Measurement of t-channel single top quark production in pp collisions Francesco Fabozzi∗ (on behalf of the CMS collaboration) INFN-Napoli & Universita della Basilicata E-mail: Francesco.Fabozzi@cern.ch Measurements of t-channel single top quark production in proton-proton collisions at the LHC at center-of-mass energies of 7 and 8 TeV, using data collected with the CMS experiment during the years 2011 and 2012, are presented. The analyses consider final states where the W boson from the top quark decays into electron-neutrino or muon-neutrino, and makes use of kinematic characteristics of electroweak single top production for the separation of signal from backgrounds using multivariate methods. The results are compared with the most precise Standard Model theory predictions. Measurements of top/anti-top cross section ratio and of various differential single top quark production cross sections are also presented. The European Physical Society Conference on High Energy Physics 22–29 July 2015 Vienna, Austria

A review of experimental data on charmoniumproduction that were obtained in fixed-target experiments at the SPS synchrotron and in proton-proton collisions and in collisions of lead nuclei in beams of the Large Hadron Collider (LHC) at CERN (Switzerland) is presented. A comparison with data obtained at the Brookhaven National Laboratory (USA) from experiments at the Relativistic Heavy Ion Collider (RHIC) is performed. Measurement of the suppression of J/ψ-meson production as a possible signal of the production of quark-gluon plasmawas proposed back in 1986 by T. Matsui and H. Satz. An anomalous suppression of J/ψ-meson production was discovered by the NA50 Collaboration at SPS (CERN) in central collisions of lead nuclei at the c.m. collision energy of 158 GeV per nucleon. Data obtained at the c.m. energy of 200 GeV per nucleon in the PHENIX experiment at RHIC indicate that, depending on multiplicity, the suppression of J/ψ-meson production at this energy approximately corresponds to the suppression of J/ψ-meson production in collisions of lead nuclei at the SPS accelerator. Theoretical models that take into account the regeneration of J/ψ mesons describe better RHIC experimental data. The measurement of charmonium production in proton-proton collisions and in collisions of lead nuclei in LHC beams revealed the importance of taking into account the regeneration process. At the LHC energies, it is also necessary to take into account the contribution of B-meson decays. Future measurements of charmonium production at the LHC to a higher statistical precision and over an extended energy region would be of importance for obtaining deeper insight into the mechanism of charmonium production and for studying the properties of matter at high energy density and temperature.

The Compact Muon Solenoid (CMS) is fully equipped to measure leptonic decays of electroweak probes in the high multiplicity environment of nucleus-nucleus collisions. Electroweak boson production is an important benchmark process at hadron colliders. Precise measurements of W and Z production in heavy-ion collisions can help to constrain nuclear PDFs as well as serve as a standard candle of the initial state in PbPb collisions at the LHC energies. The inclusive and differential measurements of the Z boson yield in the muon and electron decay channel will be presented, establishing that no modification is observed with respect to pp collisions, scaled by the number of incoherent nucleon-nucleon collisions.

Breakdown of [formula omitted]-factorization and [formula omitted] production in dA collisions

Open charm and beauty production in photon-photon collisions at L3

The LHC Run 1 results of the analysis of charmonium production in pp, pPb and PbPb collisions with the CMS experiment are reported. The coherent J/ψ photoproduction cross section is measured as a function of rapidity in ultra-peripheral PbPb collisions at 2.76 TeV. The forward-backward ratio of prompt J/ψ yields in pPb collisions at 5.02 TeV is presented as a function of the event activity and pT. The nuclear modification factor of prompt J/ψ in PbPb collisions at 2.76 TeV is shown as a function of rapidity, centrality and pT. Finally, the ratio of ψ(2S) to J/ψ yields in PbPb collisions with respect to pp collisions at 2.76 TeV is analysed in different rapidity and centrality bins.

Exclusive processes provide a useful method to study a broad range of high energy physics fields from gluon density evolutions to searches for new physics. Three measurements from the Compact Muon Solenoid experiment are reviewed. Exclusive π π production is studied in proton–proton collisions. Low-mass meson resonances are observed in the invariant mass distribution of pion pairs. The total exclusive π + π − cross-section is also measured in the p T ( π ) > 0 . 2 GeV, | y | < 2 region, yielding 26.5 ± 0.3 ( stat ) ± 5.0 ( syst ) ± 1.1 ( lumi ) μ b. The photoproduction of Y ( n S ) mesons is observed in ultraperipheral pPb collisions. The differential cross-sections are measured as a function of | t | and y. The comparison with previous measurements and theoretical models provides a better understanding of the gluon density evolution at low x values. Evidence for the γ γ → W + W − process is shown with a 3.7 σ observed significance. According to the results, limits on anomalous quartic gauge couplings can be provided.

We report on results of tcharge asymmetry measurements in the electron+jets and muon+jets channels, based on a dataset corresponding to an integrated luminosity of 5 fb 1 . The data have been collected with the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC) at CERN at a centre-of-mass energy of 7 TeV. An inclusive measurement of the tcharge asymmetry and three differential measurements as a function of the invariant mass, the transverse momentum, and the rapidity of the tsystem are presented. All measurements are in agreement with the predictions of the standard model.

Bottomonium production in pp, pPb and PbPb collisions with CMS

The measurement of t-channel single top cross-section in proton–proton collisions at the Large Hadron Collider (LHC) at a centre-of-mass energy of 7 TeV, using data collected with the Compact Muon Solenoid (CMS) experiment during the year 2010 is presented. Both the electron-neutrino and muon-neutrino decay channels of W boson from top decay are considered. Two complementary multivariate analysis methods to separate signal and background and to extract the cross-section for the single top produced in t-channel are explored. The result is compared with the most precise Standard Model theory predictions.

This PhD thesis presents two experimental particle physics analyses, the measurements of the production of a W boson in association with jets (W+jets) in proton-proton collisions using the muon decay channel and the search for resonant Higgs pair (diHiggs/double Higgs) production in proton-proton collisions using the bbZ(ll)Z(jj) final state. Both analyses use data recorded by the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC). The W+jets analysis uses data from the proton-proton collisions at a center-of-mass energy (√s) of 8 TeV and 13 TeV collected during the LHC RunI and RunII (2015) periods, corresponding to an integrated luminosity of 19.6 fb-1 and 2.2 fb-1 respectively. The measured cross sections are reported as functions of jet multiplicity, jet transverse momenta (pT), jet pseudorapidity (η), and the scalar sum of jet transverse momenta (HT) for different jet multiplicities. Distributions of the angular correlations between the jets and the muon are examined, as well as the average number of jets as a function of HT and as a function of angular variables. The measurements are compared to the theoretical predictions from next-to(-next-to)-leading-order calculations and event simulations that utilize matrix element calculations interfaced with parton showers. The Higgs pair production analysis uses data at √s = 13 TeV collected in the LHC RunII (2016) period, corresponding to an integrated luminosity of 35.9 fb-1. The bbZZ final state considered here is the one where one Z decays into two oppositely charged leptons, and the other Z decays hadronically into two or more jets. Upper limits at 95% confidence level are placed on the production cross section of narrow-width spin-0 and spin-2 particles decaying to Higgs boson pairs. This is the first search of its kind in this final state. In addition to the analysis work, the thesis also describes the work of maintaining the conditions data and support the operation of the CMS Cathode Strip Chamber (CSC), which is the main sub-detector for measuring muons in the forward/backward regions and thus a critical detector for these analyses.

The study of beauty production in heavy-ion collisions is considered to be one of the key measurement to address the flavour-dependence of in-medium energy loss in PbPb collisions. The Compact Muon Solenoid (CMS) experiment has excellent capabilities for measuring b-quark production thanks to the excellent performances of its muon and tracker system. In this talk, the measurement of nuclear modification factor of fully reconstructed B mesons for the first time in pp and PbPb collisions at 5.02 TeV as a function of transverse momentum will be presented.

Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the Compact Muon Solenoid (CMS) detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7μb−1. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cutoff used in this study (jet pT=120 GeV/c) up to the statistical limit of the available data sample (jet pT≈210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.8 MoreReceived 10 February 2011DOI:https://doi.org/10.1103/PhysRevC.84.024906This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.©2011 CERN, for the CMS Collaboration