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Open Access Publications from the University of California

Scholarly Works (10 results)

  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2018)
Measurements of Bs2∗(5840)0 and Bs1(5830)0 mesons are performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of , collected with the CMS detector at the LHC at a centre-of-mass energy of 8TeV . The analysis studies P-wave Bs0 meson decays into B(∗)+K- and B(∗)0KS0 , where the B+ and B0 mesons are identified using the decays B+→J/ψK+ and B0→J/ψK∗(892)0 . The masses of the P-wave Bs0 meson states are measured and the natural width of the Bs2∗(5840)0 state is determined. The first measurement of the mass difference between the charged and neutral B∗ mesons is also presented. The Bs2∗(5840)0 decay to B0KS0 is observed, together with a measurement of its branching fraction relative to the Bs2∗(5840)0→B+K- decay.
    Cover page: Studies of Bs2∗(5840)0 and Bs1(5830)0 mesons including the observation of the Bs2∗(5840)0→B0KS0 decay in proton-proton collisions at s=8TeVCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2020)
    New sets of CMS underlying-event parameters ("tunes") are presented for the pythia8 event generator. These tunes use the NNPDF3.1 parton distribution functions (PDFs) at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) orders in perturbative quantum chromodynamics, and the strong coupling evolution at LO or NLO. Measurements of charged-particle multiplicity and transverse momentum densities at various hadron collision energies are fit simultaneously to determine the parameters of the tunes. Comparisons of the predictions of the new tunes are provided for observables sensitive to the event shapes at LEP, global underlying event, soft multiparton interactions, and double-parton scattering contributions. In addition, comparisons are made for observables measured in various specific processes, such as multijet, Drell-Yan, and top quark-antiquark pair production including jet substructure observables. The simulation of the underlying event provided by the new tunes is interfaced to a higher-order matrix-element calculation. For the first time, predictions from pythia8 obtained with tunes based on NLO or NNLO PDFs are shown to reliably describe minimum-bias and underlying-event data with a similar level of agreement to predictions from tunes using LO PDF sets.
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2019)
      A search is presented for resonant production of second-generation sleptons ( μ ~ L , ν ~ μ ) via the R-parity-violating coupling λ 211 ' to quarks, in events with two same-sign muons and at least two jets in the final state. The smuon (muon sneutrino) is expected to decay into a muon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton-proton collisions at s = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb - 1 . No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730 fb , are derived in the context of two simplified models representing the dominant signal contributions leading to a same-sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with λ 211 ' as the only nonzero R-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.
        • 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
          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=13TeVCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Riverside Previously Published Works (2019)
            A search for the pair production of heavy vector-like partners T and B of the top and bottom quarks has been performed by the CMS experiment at the CERN LHC using proton-proton collisions at s=13Te . The data sample was collected in 2016 and corresponds to an integrated luminosity of 35.9 fb-1 . Final states studied for TT¯ production include those where one of the T quarks decays via T→tZ and the other via T→bW , tZ , or tH , where H is a Higgs boson. For the BB¯ case, final states include those where one of the B quarks decays via B→bZ and the other B→tW , bZ , or bH . Events with two oppositely charged electrons or muons, consistent with coming from the decay of a Z boson, and jets are investigated. The number of observed events is consistent with standard model background estimations. Lower limits at 95% confidence level are placed on the masses of the T and B quarks for a range of branching fractions. Assuming 100% branching fractions for T→tZ , and B→bZ , T and B quark mass values below 1280 and 1130 Ge , respectively, are excluded.
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2019)
              A search is presented for a heavy pseudoscalar boson A decaying to a Z  boson and a Higgs boson with mass of 125 GeV . In the final state considered, the Higgs boson decays to a bottom quark and antiquark, and the Z  boson decays either into a pair of electrons, muons, or neutrinos. The analysis is performed using a data sample corresponding to an integrated luminosity of 35.9 fb-1 collected in 2016 by the CMS experiment at the LHC from proton-proton collisions at a center-of-mass energy of 13 Te . The data are found to be consistent with the background expectations. Exclusion limits are set in the context of two-Higgs-doublet models in the A boson mass range between 225 and 1000 GeV .
                Cover page: Search for a heavy pseudoscalar boson decaying to a Z and a Higgs boson at s=13TeCreative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2019)
                A search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks is performed in proton-proton collisions at a center-of-mass energy of 13 Te collected with the CMS detector at the LHC. The analyzed data sample corresponds to an integrated luminosity of 35.9 fb - 1 . The signal is characterized by a large missing transverse momentum recoiling against a bottom quark-antiquark system that has a large Lorentz boost. The number of events observed in the data is consistent with the standard model background prediction. Results are interpreted in terms of limits both on parameters of the type-2 two-Higgs doublet model extended by an additional light pseudoscalar boson a (2HDM+ a ) and on parameters of a baryonic Z ' simplified model. The 2HDM+ a model is tested experimentally for the first time. For the baryonic Z ' model, the presented results constitute the most stringent constraints to date.
                  • 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
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2020)
                    New sets of CMS underlying-event parameters ("tunes") are presented for the pythia8 event generator. These tunes use the NNPDF3.1 parton distribution functions (PDFs) at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) orders in perturbative quantum chromodynamics, and the strong coupling evolution at LO or NLO. Measurements of charged-particle multiplicity and transverse momentum densities at various hadron collision energies are fit simultaneously to determine the parameters of the tunes. Comparisons of the predictions of the new tunes are provided for observables sensitive to the event shapes at LEP, global underlying event, soft multiparton interactions, and double-parton scattering contributions. In addition, comparisons are made for observables measured in various specific processes, such as multijet, Drell-Yan, and top quark-antiquark pair production including jet substructure observables. The simulation of the underlying event provided by the new tunes is interfaced to a higher-order matrix-element calculation. For the first time, predictions from pythia8 obtained with tunes based on NLO or NNLO PDFs are shown to reliably describe minimum-bias and underlying-event data with a similar level of agreement to predictions from tunes using LO PDF sets.
                      Cover page: Extraction and validation of a new set of CMS pythia8 tunes from underlying-event measurementsCreative Commons 'BY' version 4.0 license
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