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Open Access Publications from the University of California

Scholarly Works (11 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2018)
A measurement is presented of the Z/γ∗→ττ cross section in pp collisions at s=13TeV , using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 2.3fb-1 . The product of the inclusive cross section and branching fraction is measured to be σ(pp→Z/γ∗+X)B(Z/γ∗→ττ)=1848±12(stat)±67(syst \,+\,lumi) pb , in agreement with the standard model expectation, computed at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics. The measurement is used to validate new analysis techniques relevant for future measurements of τ lepton production. The measurement also provides the reconstruction efficiency and energy scale for τ decays to hadrons +ντ final states, determined with respective relative uncertainties of 2.2 and 0.9%.
    Cover page: Measurement of the Z/γ∗→ττ cross section in pp collisions at s=13TeV and validation of τ lepton analysis techniques
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    A search is presented for an excess of events with heavy-flavor quark pairs ( tt¯ and bb¯ ) and a large imbalance in transverse momentum in data from proton-proton collisions at a center-of-mass energy of 13 TeV . The data correspond to an integrated luminosity of 2.2 fb-1 collected with the CMS detector at the CERN LHC. No deviations are observed with respect to standard model predictions. The results are used in the first interpretation of dark matter production in tt¯ and bb¯ final states in a simplified model. This analysis is also the first to perform a statistical combination of searches for dark matter produced with different heavy-flavor final states. The combination provides exclusions that are stronger than those achieved with individual heavy-flavor final states.
      Cover page: Search for dark matter produced in association with heavy-flavor quark pairs in proton-proton collisions at s=13TeV
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2017)
      The production cross section of a W boson in association with two b jets is measured using a sample of proton-proton collisions at [Formula: see text] collected by the CMS experiment at the CERN LHC. The data sample corresponds to an integrated luminosity of 19.8[Formula: see text]. The W bosons are reconstructed via their leptonic decays, [Formula: see text], where [Formula: see text] or [Formula: see text]. The fiducial region studied contains exactly one lepton with transverse momentum [Formula: see text] and pseudorapidity [Formula: see text], with exactly two b jets with [Formula: see text] and [Formula: see text] and no other jets with [Formula: see text] and [Formula: see text]. The cross section is measured to be [Formula: see text]+[Formula: see text], in agreement with standard model predictions.
        Cover page: Measurement of the production cross section of a W boson in association with two b jets in pp collisions at s=8TeV
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2017)
        A data sample of events from proton-proton collisions with two isolated same-sign leptons, missing transverse momentum, and jets is studied in a search for signatures of new physics phenomena by the CMS Collaboration at the LHC. The data correspond to an integrated luminosity of 35.9 fb-1 , and a center-of-mass energy of 13 TeV . The properties of the events are consistent with expectations from standard model processes, and no excess yield is observed. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos, squarks, and same-sign top quarks, as well as top-quark associated production of a heavy scalar or pseudoscalar boson decaying to top quarks, and on the standard model production of events with four top quarks. The observed lower mass limits are as high as 1500 GeV for gluinos, 830 GeV for bottom squarks. The excluded mass range for heavy (pseudo)scalar bosons is 350-360 (350-410) GeV . Additionally, model-independent limits in several topological regions are provided, allowing for further interpretations of the results.
          Cover page: Search for physics beyond the standard model in events with two leptons of same sign, missing transverse momentum, and jets in proton–proton collisions at s=13TeVCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2018)
          A search for new physics in events with a Z boson produced in association with large missing transverse momentum at the LHC is presented. The search is based on the 2016 data sample of proton-proton collisions recorded with the CMS experiment at s=13TeV , corresponding to an integrated luminosity of 35.9 fb-1 . The results of this search are interpreted in terms of a simplified model of dark matter production via spin-0 or spin-1 mediators, a scenario with a standard-model-like Higgs boson produced in association with the Z boson and decaying invisibly, a model of unparticle production, and a model with large extra spatial dimensions. No significant deviations from the background expectations are found, and limits are set on relevant model parameters, significantly extending the results previously achieved in this channel.
            Cover page: Search for new physics in events with a leptonically decaying Z boson and a large transverse momentum imbalance in proton–proton collisions at s = 13TeVCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2017)
            The cross section of top quark-antiquark pair production in proton-proton collisions at [Formula: see text] is measured by the CMS experiment at the LHC, using data corresponding to an integrated luminosity of 2.2[Formula: see text]. The measurement is performed by analyzing events in which the final state includes one electron, one muon, and two or more jets, at least one of which is identified as originating from hadronization of a b quark. The measured cross section is [Formula: see text], in agreement with the expectation from the standard model.
              Cover page: Measurement of the tt¯ production cross section using events in the eμ final state in pp collisions at s=13TeVCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2017)
              The WZ production cross section is measured by the CMS experiment at the CERN LHC in proton-proton collision data samples corresponding to integrated luminosities of 4.9[Formula: see text] collected at [Formula: see text], and 19.6[Formula: see text] at [Formula: see text]. The measurements are performed using the fully-leptonic WZ decay modes with electrons and muons in the final state. The measured cross sections for [Formula: see text] are [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text]. Differential cross sections with respect to the [Formula: see text] boson [Formula: see text], the leading jet [Formula: see text], and the number of jets are obtained using the [Formula: see text] data. The results are consistent with standard model predictions and constraints on anomalous triple gauge couplings are obtained.
                Cover page: Measurement of the WZ production cross section in pp collisions at [Formula: see text] and 8[Formula: see text] and search for anomalous triple gauge couplings at [Formula: see text].Creative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2018)
                A study of the associated production of a Z boson and a charm quark jet ( Z+c ), and a comparison to production with a b quark jet ( Z+b ), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb-1 , collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with pTℓ>20GeV , |ηℓ|<2.1 , 7125GeV and |ηjet|<2.5 . The Z+c production cross section is measured to be σ(pp→Z+c+X)B(Z→ℓ+ℓ-)=8.8±0.5(stat)±0.6(syst)pb . The ratio of the Z+c and Z+b production cross sections is measured to be σ(pp→Z+c+X)/σ(pp→Z+b+X)=2.0±0.2(stat)±0.2(syst) . The Z+c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.
                  Cover page: Measurement of associated Z + charm production in proton–proton collisions at s=8TeVCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2017)
                  A search for heavy resonances with masses above 1 TeV , decaying to final states containing a vector boson and a Higgs boson, is presented. The search considers hadronic decays of the vector boson, and Higgs boson decays to b quarks. The decay products are highly boosted, and each collimated pair of quarks is reconstructed as a single, massive jet. The analysis is performed using a data sample collected in 2016 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV , corresponding to an integrated luminosity of 35.9 fb-1 . The data are consistent with the background expectation and are used to place limits on the parameters of a theoretical model with a heavy vector triplet. In the benchmark scenario with mass-degenerate W' and Z' bosons decaying predominantly to pairs of standard model bosons, for the first time heavy resonances for masses as high as 3.3 TeV are excluded at 95% confidence level, setting the most stringent constraints to date on such states decaying into a vector boson and a Higgs boson.
                    Cover page: Search for heavy resonances that decay into a vector boson and a Higgs boson in hadronic final states at s=13TeVCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2018)
                    The nuclear modification factors of J/ψ and ψ(2S) mesons are measured in PbPb collisions at a centre-of-mass energy per nucleon pair of sNN=5.02TeV . The analysis is based on PbPb and pp data samples collected by CMS at the LHC in 2015, corresponding to integrated luminosities of 464 μb-1 and 28 pb-1 , respectively. The measurements are performed in the dimuon rapidity range of |y|<2.4 as a function of centrality, rapidity, and transverse momentum ( pT ) from pT=3 GeV/c in the most forward region and up to 50 GeV/c . Both prompt and nonprompt (coming from b hadron decays) J/ψ mesons are observed to be increasingly suppressed with centrality, with a magnitude similar to the one observed at sNN=2.76TeV for the two J/ψ meson components. No dependence on rapidity is observed for either prompt or nonprompt J/ψ mesons. An indication of a lower prompt J/ψ meson suppression at pT>25 GeV/c is seen with respect to that observed at intermediate pT . The prompt ψ(2S) meson yield is found to be more suppressed than that of the prompt J/ψ mesons in the entire pT range.
                      Cover page: Measurement of prompt and nonprompt charmonium suppression in PbPb collisions at 5.02TeVCreative Commons 'BY' version 4.0 license
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