To sustain and extend its discovery potential, the Large Hadron Collider (LHC) will undergo a major upgrade in the coming years, referred to as High Luminosity LHC (HLLHC), aimed to increase its ...instantaneous luminosity, 5 times larger than the designed limit, and, consequently leading to high levels of radiation, with the goal to collect 10 times larger the original designed integrated luminosity. The drift tube chambers (DT) of CMS muon detector system is built to proficiently measure and trigger on muons in the harsh radiation environment expected during the HL-LHC era. Ageing studies are performed at the CERNs gamma ray irradiation facility (GIF++) by measuring the muon hit efficiency of these detectors at various LHC operation conditions. One such irradiation campaign was started in October 2017, when a spare MB2 chamber moved inside the bunker and irradiated at lower acceleration factors. Two out of twelve layers of the DT chamber were operated while being irradiated with the radioactive source and then their muon hit efficiency was calculated in coincidence with other ten layers which were kept on the standby. The chamber absorbed an integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway and strategies to mitigate the aging effects are also being developed. The effect of radiation on the performance of DT chamber and its impact on the overall muon reconstruction efficiency expected during the HL-LHC are presented.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A measurement of the cross section for top quark-antiquark (...) pairs produced in association with a photon in ...proton-proton collisions at ... TeV is presented. The analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.7 fb1. The signal is defined as the production of a ... pair in association with a photon having a transverse energy larger than 25 GeV and an absolute pseudorapidity smaller than 1.44. The measurement is performed in the fiducial phase space corresponding to the semileptonic decay chain of the ... pair, and the cross section is measured relative to the inclusive ... pair production cross section. The fiducial cross section for associated ... pair and photon production is found to be 127 ±27 (stat+syst) fb per semileptonic final state. The measured value is in agreement with the theoretical prediction. Figure not available: see fulltext.
The CMS drift tubes (DT) muon detector, built for withstanding the LHC expected integrated and instantaneous luminosities, will be used also in the High Luminosity LHC (HL-LHC) at a 5 times larger ...instantaneous luminosity and, consequently, much higher levels of radiation, reaching about 10 times the LHC integrated luminosity. Initial irradiation tests of a spare DT chamber at the CERN gamma irradiation facility (GIF++), at large (\(\sim\)O(100)) acceleration factor, showed ageing effects resulting in a degradation of the DT cell performance. However, full CMS simulations have shown almost no impact in the muon reconstruction efficiency over the full barrel acceptance and for the full integrated luminosity. A second spare DT chamber was moved inside the GIF++ bunker in October 2017. The chamber was being irradiated at lower acceleration factors, and only 2 out of the 12 layers of the chamber were switched at working voltage when the radioactive source was active, being the other layers in standby. In this way the other non-aged layers are used as reference and as a precise and unbiased telescope of muon tracks for the efficiency computation of the aged layers of the chamber, when set at working voltage for measurements. An integrated dose equivalent to two times the expected integrated luminosity of the HL-LHC run has been absorbed by this second spare DT chamber and the final impact on the muon reconstruction efficiency is under study. Direct inspection of some extracted aged anode wires presented a melted resistive deposition of materials. Investigation on the outgassing of cell materials and of the gas components used at the GIF++ are underway. Strategies to mitigate the ageing effects are also being developed. From the long irradiation measurements of the second spare DT chamber, the effects of radiation in the performance of the DTs expected during the HL-LHC run will be presented.
Abstract Production of prompt J/psi meson pairs in proton-proton collisions at ... = 7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of ...about 4.7 fb-1. The two J/psi mesons are fully reconstructed via their decays into mu + mu - pairs. This observation provides for the first time access to the high-transverse-momentum region of J/psi pair production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/psi transverse momentum (p T J/psi) and rapidity (|y J/psi|): |y J/psi | < 1.2 for p T J/psi > 6.5 GeV/c; 1.2 < |y J/psi| < 1.43 for a p T threshold that scales linearly with |y J/psi| from 6.5 to 4.5 GeV/c; and 1.43 < |y J/psi| < 2.2 for p T J/psi > 4.5 GeV/c. The total cross section, assuming unpolarized prompt J/psi pair production is 1.49 ± 0.07 (stat) ±0.13 (syst) nb. Different assumptions about the J/psi polarization imply modifications to the cross section ranging from -31% to +27%. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A measurement of the triple-differential cross section, ..., in photon + jets final states using a data sample ...from proton-proton collisions at ... = 7 TeV is presented. This sample corresponds to an integrated luminosity of 2.14 fb^sup -1^ collected by the CMS detector at the LHC. Photons and jets are reconstructed within a pseudorapidity range of |eta| < 2.5, and are required to have transverse momenta in the range 40 < ... < 300 GeV and ... > 30 GeV, respectively. The measurements are compared to theoretical predictions from the sherpa leading-order QCD Monte Carlo event generator and the next-to-leading-order perturbative QCD calculation from jetphox. The predictions are found to be consistent with the data over most of the examined kinematic region. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract The ... charge asymmetry in proton-proton collisions at ... = 7 TeV is measured using the dilepton decay channel ...(ee, emu, or mumu). The data correspond to a total integrated luminosity of 5.0 fb^sup -1^, collected by the CMS experiment at the LHC. The tt and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be A ^sub C^ = -0.010 ± 0.017 (stat.) ± 0.008 (syst.) and ... = 0.009 ± 0.010 (stat.) ± 0.006 (syst.). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the ... system. All measurements are consistent with the expectations of the standard model. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract The production of ...(1S), ...(2S), and ...(3S) is investigated in pPb and pp collisions at centre-of-mass ...energies per nucleon pair of 5.02 TeV and 2.76 TeV, respectively. The datasets correspond to integrated luminosities of about 31 nb^sup -1^ (pPb) and 5.4 pb^sup -1^ (pp), collected in 2013 by the CMS experiment at the LHC. Upsilons that decay into muons are reconstructed within the rapidity interval |y ^sub CM^| < 1.93 in the nucleon-nucleon centre-of-mass frame. Their production is studied as a function of two measures of event activity, namely the charged-particle multiplicity measured in the pseudorapidity interval |eta| < 2.4, and the sum of transverse energy deposited at forward pseudorapidity, 4.0 < |eta| < 5.2. The ... cross sections normalized by their event activity integrated values, ...(nS)/...(nS), are found to rise with both measures of the event activity in pp and pPb. In both collision systems, the ratios of the excited to the ground state cross sections, ...(nS)/ ...(1S), are found to decrease with the charged-particle multiplicity, while as a function of the transverse energy the variation is less pronounced. The event activity integrated double ratios, ...(nS)/ ...(1S)^sub pPb^ /...(nS)/ ...(1S)^sub pp^, are also measured and found to be 0.83 ± 0.05 (stat.) ± 0.05 (syst.) and 0.71 ± 0.08 (stat.) ± 0.09 (syst.) for ...(2S) and ...(3S), respectively. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A detailed description is reported of the analysis used by the CMS Collaboration in the search for the standard ...model Higgs boson in pp collisions at the LHC, which led to the observation of a new boson. The data sample corresponds to integrated luminosities up to 5.1 fb^sup -1^ at ... TeV, and up to 5.3 fb^sup -1^ at ... TeV. The results for five Higgs boson decay modes γγ, ZZ, WW, ττ, and bb, which show a combined local significance of 5 standard deviations near 125 GeV, are reviewed. A fit to the invariant mass of the two high resolution channels, γγ and ZZ arrow right 4, gives a mass estimate of 125.3 ± 0.4 (stat.) ± 0.5 (syst.) GeV. The measurements are interpreted in the context of the standard model Lagrangian for the scalar Higgs field interacting with fermions and vector bosons. The measured values of the corresponding couplings are compared to the standard model predictions. The hypothesis of custodial symmetry is tested through the measurement of the ratio of the couplings to the W and Z bosons. All the results are consistent, within their uncertainties, with the expectations for a standard model Higgs boson. Figure not available: see fulltext.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract Figure not available: see fulltext. The production of the X(3872) is studied in pp collisions at ... TeV, using ...decays to J/ψπ ^sup +^ pi ^sup -^, where the J/psi decays to two muons. The data were recorded by the CMS experiment and correspond to an integrated luminosity of 4.8 fb^sup -1^. The measurements are performed in a kinematic range in which the X(3872) candidates have a transverse momentum 10<p ^sub T^ <50 GeV and rapidity |y|<1.2. The ratio of the X(3872) and psi(2S) cross sections times their branching fractions into J/ψπ ^sup +^ pi ^sup -^ is measured as a function of p ^sub T^. In addition, the fraction of X(3872) originating from B decays is determined. From these measurements the prompt X(3872) differential cross section times branching fraction as a function of p ^sub T^ is extracted. The pi ^sup +^ pi ^sup -^ mass spectrum of the J/ψπ ^sup +^ pi ^sup -^ system in the X(3872) decays is also investigated.
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