Sneha Malde

Abstract:

Measurements of inclusive W and Z boson production cross-sections in pp collisions at √ s = 7TeV using final states containing muons are presented. The data sample corresponds to an integrated luminosity of 37 pb -1 collected with the LHCb detector. The W and Z bosons are reconstructed from muons with a transverse momentum above 20 GeV/c and pseudorapidity between 2:0 and 4:5, and, in the case of the Z cross-section, a dimuon invariant mass between 60 and 120 GeV/c2. The cross-sections are measured to be 831±9±27±29 pb for W+, 656±8±19±23 for W- and 76:7±1:7±3: 3±2:7 pb for Z, where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity. Differential cross-sections, W and Z cross-section ratios and the lepton charge asymmetry are also measured in the same kinematic region. The ratios are determined to be σW+→μ+ν/σW- →μ-ν = 1:27±0:02±0:01 and ( σW+→μ+ν+σW- →μ-ν)/σZ→μμ = 19:4±0:5± 0:9. The results are in general agreement with theoretical predictions, performed at nextto- next-to-leading order in QCD using recently calculated parton distribution functions. Copyright CERN.

Abstract:

Based on data corresponding to an integrated luminosity of 0.37 fb -1 collected by the LHCb experiment in 2011, the following ratios of branching fractions are measured: B(B0 → π+π -) / B(B0 → K+π-) = 0.262 ± 0.009 ± 0.017; (fs/fd) B(Bs0 → K +K-) / B(B0 → K+π -) = 0.316 ± 0.009 ± 0.019; (fs/fd) B(B s0 → π+K-) / B(B0 → K+π-) = 0.074 ± 0.006 ± 0.006; (fd/fs) ± B(B0 → K+K-) / B(B s0 → K+K-) = 0.018 -0.007 +-0.007 ± 0.009; (fs/fd) B(Bs0 → π+π-) / B(B0 → π+π-) = 0.050 -0.009+0.011 ± 0.004; BΛb0 → pπ-) / BΛb0 → pK-) = 0.86 ± 0.08 ± 0.05; where the πrst uncertainties are statistical and the second systematic. Using the current world average of B(B0 → K +π-π and the ratio of the strange to light neutral B meson production fs/fd measured by LHCb, we obtain: B(B0 → π+π-) = (5.08 ± 0.17 ± 0.37) × 10-6; B(Bs0 → K+K-) = (23.0 ± 0.7 ± 2.3) × 10-6; B(Bs0 → π+K-) = (5.4 ± 0.4 ± 0.6) × 10-6; B(B0 → K+K-) = (0.11 -0.04+0.05 ± 0.06) × 10 -6; B(Bs0 → π+π -) = (0.95 -0.17+0.21 ± 0.13) × 10-6. The measurements of B(Bs0 → K +K-), B(Bs0 → π+K-) and B(B0 → K+K -) are the most precise to date. The decay mode Bs0 → π+π- is observed for the first time with a significance of more than 5σ. Copyright CERN.

Abstract:

Charged particle production in proton-proton collisions is studied with the LHCb detector at a centre-of-mass energy of √s = 7 TeV in different intervals of pseudorapidity η. Charged particles are reconstructed close to the interaction region in the vertex detector, which provides high reconstruction efficiency in the η ranges −2.5 < η <−2.0 and 2.0 < η < 4.5. The data were taken with a minimum bias trigger, only requiring one or more reconstructed tracks in the vertex detector. By selecting an event sample with at least one track with a transverse momentum greater than 1 GeV/c a hard QCD subsample is investigated. Several event generators are compared with the data; none are able to describe fully the multiplicity distributions or the charged particle density distribution as a function of η. In general, the models underestimate charged particle production.

Abstract:

A study of mixing and indirect CP violation in D0 mesons through the determination of the parameters yCP and AΓ is presented. The parameter yCP is the deviation from unity of the ratio of effective lifetimes measured in D0 decays to the CP eigenstate K+K- with respect to decays to the Cabibbo favoured mode K-π+. The result measured using data collected by LHCb in 2010, corresponding to an integrated luminosity of 29 pb-1, is yCP = (5.5 ± 6.3stat ± 4.1syst) × 10 -3. The parameter AΓ is the asymmetry of effective lifetimes measured in decays of D0 and D̄0 mesons to K+K-. The result is AΓ = (-5.9 ± 5.9stat ± 2.1syst) × 10-3. A data-driven technique is used to correct for lifetime-biasing effects. Copyright CERN.

Abstract:

The production of B± mesons in proton-proton collisions at √s = 7TeVis studied using 35 pb-1 of data collected by the LHCb detector. The B± mesons are reconstructed exclusively in the B± → J/ΨK± mode, with J/Ψ→μ+μ-. The differential production cross-section is measured as a function of the B± transverse momentum in the ducial region 0 < pT < 40 GeV=c and with rapidity 2:0 < y < 4:5. The total cross-section, summing up B+ and B -, is measured to be σ(pp → B±X; 0 < pT < 40 GeV=c; 2:0 < y < 4:5) = 41:4 ± 1:5 (stat:) ± 3:1 (syst:) μb. Copyright CERN.