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.