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eScholarship
Open Access Publications from the University of California

Scholarly Works (10 results)

  • Article
  • Peer Reviewed
LBL Publications (2016)
A time-dependent angular analysis of Bs0→ψ(2S)ϕ decays is performed using data recorded by the LHCb experiment. The data set corresponds to an integrated luminosity of 3.0fb−1 collected during Run 1 of the LHC. The CP-violating phase and decay-width difference of the Bs0 system are measured to be ϕs=0.23−0.28+0.29±0.02rad and ΔΓs=0.066−0.044+0.041±0.007ps−1, respectively, where the first uncertainty is statistical and the second systematic. This is the first time that ϕs and ΔΓs have been measured in a decay containing the ψ(2S) resonance.
    • Article
    • Peer Reviewed
    LBL Publications (2017)
    The production of tt‾, W+bb‾ and W+cc‾ is studied in the forward region of proton–proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98±0.02 fb−1. The W bosons are reconstructed in the decays W→ℓν, where ℓ denotes muon or electron, while the b and c quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions.
      • Article
      • Peer Reviewed
      LBL Publications (2016)
      A search for the decays of the B+c meson to pp-π+ is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb-1 collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV. No signal is found and an upper limit, at 95% confidence level, is set, fcfu×B(B+c→ppπ+)<3.6×10-8 in the kinematic region m(pp)<2.85 GeV/c2, pT(B)<20 GeV/c and 2.0
        • Article
        • Peer Reviewed
        LBL Publications (2016)
        Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-of-mass energy of sNN=5 TeV, collected with the LHCb detector at the LHC. The analysis is based on data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Δη, and relative azimuthal angle, Δϕ, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Δϕ≈0, is observed in the pseudorapidity range 2.0<η<4.9. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to η=4.9. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
          • Article
          • Peer Reviewed
          LBL Publications (2016)
          The Λb0→Λφ decay is observed using data corresponding to an integrated luminosity of 3.0 fb-1 recorded by the LHCb experiment. The decay proceeds at leading order via a b→sss loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of 5.9 standard deviations. The value of the branching fraction is measured to be (5.18±1.04±0.35-0.62+0.67)×10-6, where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.
            • Article
            • Peer Reviewed
            LBL Publications (2017)
            A measurement of the time-integrated CP asymmetry in the Cabibbo-suppressed decay D0→K−K+ is performed using pp collision data, corresponding to an integrated luminosity of 3 fb−1, collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in D⁎+→D0π+ and D⁎−→D‾0π− decays. The time-integrated CP asymmetry ACP(K−K+) is obtained assuming negligible CP violation in charm mixing and in Cabibbo-favoured D0→K−π+, D+→K−π+π+ and D+→K‾0π+ decays used as calibration channels. It is found to be ACP(K−K+)=(0.14±0.15 (stat)±0.10 (syst))%. A combination of this result with previous LHCb measurements yields ACP(K−K+)=(0.04±0.12 (stat)±0.10 (syst))%,ACP(π−π+)=(0.07±0.14 (stat)±0.11 (syst))%. These are the most precise measurements from a single experiment. The result for ACP(K−K+) is the most precise determination of a time-integrated CP asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.
              • Article
              • Peer Reviewed
              LBL Publications (2017)
              A search for the CP-violating strong decays η→π+π− and η'(958)→π+π− has been performed using approximately 2.5×107 events of each of the decays D+→π+π+π− and Ds+→π+π+π−, recorded by the LHCb experiment. The data set corresponds to an integrated luminosity of 3.0 fb−1 of pp collision data recorded during LHC Run 1 and 0.3 fb−1 recorded in Run 2. No evidence is seen for D(s)+→π+η(') with η(')→π+π−, and upper limits at 90% confidence level are set on the branching fractions, B(η→π+π−)<1.6×10−5 and B(η'→π+π−)<1.8×10−5. The limit for the η decay is comparable with the existing one, while that for the η' is a factor of three smaller than the previous limit.
                • Article
                • Peer Reviewed
                LBL Publications (2016)
                Using a data set corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV, the effective lifetime in the Bs0→J/ψη decay mode, τeff, is measured to beτeff=1.479±0.034 (stat)±0.011 (syst) ps. Assuming CP conservation, τeff corresponds to the lifetime of the light Bs0 mass eigenstate. This is the first measurement of the effective lifetime in this decay mode.
                  • Article
                  • Peer Reviewed
                  LBL Publications (2017)
                  The observation of the decay Ξb−→J/ψΛK− is reported, using a data sample corresponding to an integrated luminosity of 3fb−1, collected by the LHCb detector in pp collisions at centre-of-mass energies of 7 and 8TeV. The production rate of Ξb− baryons detected in the decay Ξb−→J/ψΛK− is measured relative to that of Λb0 baryons using the decay Λb0→J/ψΛ. Integrated over the b-baryon transverse momentum pT<25GeV/c and rapidity 2.0
                    • Article
                    • Peer Reviewed
                    LBL Publications (2017)
                    A search is made for the highly-suppressed B meson decays B+→K+K+π− and B+→π+π+K− using a data sample corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV. No evidence is found for the decays, and upper limits at 90% confidence level are determined to be B(B+→K+K+π−)<1.1×10−8 and B(B+→π+π+K−)<4.6×10−8.
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