7 research outputs found

    Measurements with silicon photomultipliers of dose-rate effects in the radiation damage of plastic scintillator tiles in the CMS hadron endcap calorimeter

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    Measurements are presented of the reduction of signal output due to radiation damage for two types of plastic scintillator tiles used in the hadron endcap (HE) calorimeter of the CMS detector. The tiles were exposed to particles produced in proton-proton (pp) collisions at the CERN LHC with a center-of-mass energy of 13 TeV, corresponding to a delivered luminosity of 50 fb-1. The measurements are based on readout channels of the HE that were instrumented with silicon photomultipliers, and are derived using data from several sources: A laser calibration system, a movable radioactive source, as well as hadrons and muons produced in pp collisions. Results from several irradiation campaigns using 60Co sources are also discussed. The damage is presented as a function of dose rate. Within the range of these measurements, for a fixed dose the damage increases with decreasing dose rate

    Observation of nuclear modifications in W-+/- boson production in pPb collisions at root s(NN)=8.16 TeV

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    The production of W\ub1 bosons is studied in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 1asNN=8.16TeV. Measurements are performed in the W\ub1\u2192\u3bc\ub1\u3bd\u3bc channel using a data sample corresponding to an integrated luminosity of 173.4\ub16.1nb 121, collected by the CMS Collaboration at the LHC. The number of positively and negatively charged W bosons is determined separately in the muon pseudorapidity region in the laboratory frame |\u3b7lab\u3bc|<2.4 and transverse momentum pT\u3bc>25GeV/c. The W\ub1 boson differential cross sections, muon charge asymmetry, and the ratios of W\ub1 boson yields for the proton-going over the Pb-going beam directions are reported as a function of the muon pseudorapidity in the nucleon-nucleon centre-of-mass frame. The measurements are compared to the predictions from theoretical calculations based on parton distribution functions (PDFs) at next-to-leading-order. The results favour PDF calculations that include nuclear modifications and provide constraints on the nuclear PDF global fits

    Search for resonant t(t)over-bar production in proton-proton collisions at root s=13 TeV

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    A search for a heavy resonance decaying into a top quark and antiquark (t t \uaf) pair is performed using proton-proton collisions at 1a s=13 TeV. The search uses the data set collected with the CMS detector in 2016, which corresponds to an integrated luminosity of 35.9 fb 121 . The analysis considers three exclusive final states and uses reconstruction techniques that are optimized for top quarks with high Lorentz boosts, which requires the use of nonisolated leptons and jet substructure techniques. No significant excess of events relative to the expected yield from standard model processes is observed. Upper limits on the production cross section of heavy resonances decaying to a t t \uaf pair are calculated. Limits are derived for a leptophobic topcolor Z \u2032 resonance with widths of 1, 10, and 30%, relative to the mass of the resonance, and exclude masses up to 3.80, 5.25, and 6.65 TeV, respectively. Kaluza-Klein excitations of the gluon in the Randall-Sundrum model are excluded up to 4.55 TeV. To date, these are the most stringent limits on t t \uaf resonances

    Search for lepton flavour violating decays of a neutral heavy Higgs boson to mu tau and e tau in proton-proton collisions at root s=13 TeV

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    A search for lepton flavour violating decays of a neutral non-standard-model Higgs boson in the \u3bc\u3c4 and e\u3c4 decay modes is presented. The search is based on proton-proton collisions at a center of mass energy s = 13 TeV collected with the CMS detector in 2016, corresponding to an integrated luminosity of 35.9 fb 121. The \u3c4 leptons are reconstructed in the leptonic and hadronic decay modes. No signal is observed in the mass range 200\u2013900 GeV. At 95% confidence level, the observed (expected) upper limits on the production cross section multiplied by the branching fraction vary from 51.9 (57.4) fb to 1.6 (2.1) fb for the \u3bc\u3c4 and from 94.1 (91.6) fb to 2.3 (2.3) fb for the e\u3c4 decay modes. [Figure not available: see fulltext.]

    Observation of Single Top Quark Production in Association with a Z Boson in Proton-Proton Collisions at root s=13 TeV

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    The observation of single top quark production in association with a Z boson and a quark (tZq) is reported. Events from proton-proton collisions at a center-of-mass energy of 13 TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed. The data were collected with the CMS detector in 2016 and 2017 and correspond to an integrated luminosity of 77.4fb-1. The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production. The tZq signal is observed with a significance well over 5 standard deviations. The measured tZq production cross section is σ(pp→tZq→t?+?-q)=111±13(stat)-9+11(syst) fb, for dilepton invariant masses above 30 GeV, in agreement with the standard model expectation

    Search for low mass vector resonances decaying into quark-antiquark pairs in proton-proton collisions at root s=13 Tev

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    A search for low mass narrow vector resonances decaying into quark-antiquark pairs is presented. The analysis is based on data collected in 2017 with the CMS detector at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 41.1 fb-1. The results of this analysis are combined with those of an earlier analysis based on data collected at the same collision energy in 2016, corresponding to 35.9 fb-1. Signal candidates will be recoiling against initial state radiation and are identified as energetic, large-radius jets with two pronged substructure. The invariant jet mass spectrum is probed for a potential narrow peaking signal over a smoothly falling background. No evidence for such resonances is observed within the mass range of 50-450 GeV. Upper limits at the 95% confidence level are set on the coupling of narrow resonances to quarks, as a function of the resonance mass. For masses between 50 and 300 GeV these are the most sensitive limits to date. This analysis extends the earlier search to a mass range of 300-450 GeV, which is probed for the first time with jet substructure techniques
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