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Open Access Publications from the University of California

Scholarly Works (15 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2018)
This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair (tt) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centreof- mass energies of 7 and 8TeV. The data correspond to integrated luminosities of about 5 and 20 fb–1for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are ACLHC7= 0:005±0:007 (stat) ±0:006 (syst) at 7TeV and ACLHC7= 0:0055 ± 0:0023 (stat) ± 0:0025 (syst) at 8TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the [formula presented] system at 8TeV, are consistent with the respective standard model predictions.
    Cover page: Combination of inclusive and differential tt¯ charge asymmetry measurements using ATLAS and CMS data at √s = 7 and 8 TeV
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    A search for new phenomena is performed using events with jets and significant transverse momentum imbalance, as inferred through the MT2 variable. The results are based on a sample of proton-proton collisions collected in 2016 at a center-of-mass energy of 13 TeV with the CMS detector and corresponding to an integrated luminosity of 35.9 fb-1 . No excess event yield is observed above the predicted standard model background, and the results are interpreted as exclusion limits at 95% confidence level on the masses of predicted particles in a variety of simplified models of R-parity conserving supersymmetry. Depending on the details of the model, 95% confidence level lower limits on the gluino (light-flavor squark) masses are placed up to 2025 (1550) GeV . Mass limits as high as 1070 (1175) GeV are set on the masses of top (bottom) squarks. Information is provided to enable re-interpretation of these results, including model-independent limits on the number of non-standard model events for a set of simplified, inclusive search regions.
      Cover page: Search for new phenomena with the MT2 variable in the all-hadronic final state produced in proton–proton collisions at s=13TeV
      • 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 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=13TeV
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2018)
          A search for pair production of heavy scalar leptoquarks (LQs), each decaying into a top quark and a τ lepton, is presented. The search considers final states with an electron or a muon, one or two τ leptons that decayed to hadrons, and additional jets. The data were collected in 2016 in proton-proton collisions at s=13Te with the CMS detector at the LHC, and correspond to an integrated luminosity of 35.9 fb-1 . No evidence for pair production of LQs is found. Assuming a branching fraction of unity for the decay LQ→tτ , upper limits on the production cross section are set as a function of LQ mass, excluding masses below 900 Ge at 95% confidence level. These results provide the most stringent limits to date on the production of scalar LQs that decay to a top quark and a τ lepton.
            Cover page: Search for third-generation scalar leptoquarks decaying to a top quark and a τ lepton at s=13Te
            • 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 = 13TeV
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2018)
              A measurement is presented of the associated production of a single top quark and a Z boson. The study uses data from proton–proton collisions at s=13TeV recorded by the CMS experiment, corresponding to an integrated luminosity of 35.9 fb−1. Using final states with three leptons (electrons or muons), the tZq production cross section is measured to be σ(pp→tZq→Wbℓ+ℓ−q)=123−31+33(stat)−23+29(syst)fb, where ℓ stands for electrons, muons, or τ leptons, with observed and expected significances of 3.7 and 3.1 standard deviations, respectively.
                • Article
                • Peer Reviewed
                UC Riverside Previously Published Works (2018)
                A search is presented for physics beyond the standard model, based on measurements of dijet angular distributions in proton-proton collisions at s=13TeV . The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 35.9 fb-1 . The observed distributions, corrected to particle level, are found to be in agreement with predictions from perturbative quantum chromodynamics that include electroweak corrections. Constraints are placed on models containing quark contact interactions, extra spatial dimensions, quantum black holes, or dark matter, using the detector-level distributions. In a benchmark model where only left-handed quarks participate, contact interactions are excluded at the 95% confidence level up to a scale of 12.8 or 17.5TeV, for destructive or constructive interference, respectively. The most stringent lower limits to date are set on the ultraviolet cutoff in the Arkani-Hamed-Dimopoulos-Dvali model of extra dimensions. In the Giudice-Rattazzi-Wells convention, the cutoff scale is excluded up to 10.1TeV. The production of quantum black holes is excluded for masses below 5.9 and 8.2TeV, depending on the model. For the first time, lower limits between 2.0 and 4.6TeVare set on the mass of a dark matter mediator for (axial-)vector mediators, for the universal quark coupling gq=1.0 .
                  Cover page: Search for new physics in dijet angular distributions using proton–proton collisions at s=13TeV and constraints on dark matter and other models
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2018)
                  Measurements are presented of the lifetimes of the B0 , Bs0 , Λb0 , and Bc+ hadrons using the decay channels B0→J/ψK∗(892)0 , B0→J/ψKS0 , Bs0→J/ψπ+π- , Bs0→J/ψϕ(1020) , Λb0→J/ψΛ0 , and Bc+→J/ψπ+ . The data sample, corresponding to an integrated luminosity of 19.7 fb-1 , was collected by the CMS detector at the LHC in proton-proton collisions at s=8TeV . The B0 lifetime is measured to be 453.0±1.6(stat)±1.8(syst)μm in J/ψK∗(892)0 and 457.8±2.7(stat)±2.8(syst)μm in J/ψKS0 , which results in a combined measurement of cτB0=454.1±1.4(stat)±1.7(syst)μm . The effective lifetime of the Bs0 meson is measured in two decay modes, with contributions from different amounts of the heavy and light eigenstates. This results in two different measured lifetimes: cτBs0→J/ψπ+π-=502.7±10.2(stat)±3.4(syst)μm and cτBs0→J/ψϕ(1020)=443.9±2.0(stat)±1.5(syst)μm . The Λb0 lifetime is found to be 442.9±8.2(stat)±2.8(syst)μm . The precision from each of these channels is as good as or better than previous measurements. The Bc+ lifetime, measured with respect to the B+ to reduce the systematic uncertainty, is 162.3±7.8(stat)±4.2(syst)±0.1(τB+)μm . All results are in agreement with current world-average values.
                    Cover page: Measurement of b hadron lifetimes in pp collisions at s=8TeV
                    • Article
                    • Peer Reviewed
                    UC Riverside Previously Published Works (2019)
                    In both panels of figure 11, the unit of the z axis was mistakenly written as “pb” when it should have been “fb”. The corrected versions are shown in figure 1.
                      Cover page: Erratum to: Search for a new scalar resonance decaying to a pair of Z bosons in proton-proton collisions at s=13 TeV
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