Guy Wilkinson

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.

Abstract:

The isospin asymmetries of B → K(*)μ +μ- decays and the partial branching fractions of B0 → K0μ+μ- and B +→ K*+μ+μ- are measured as a function of the di-muon mass squared q2 using an integrated luminosity of 1.0fb-1 collected with the LHCb detector. The B → Kμ+μ- isospin asymmetry integrated over q2 is negative, deviating from zero with over 4 σ significance. The B → K*μ+μ- decay measurements are consistent with the Standard Model prediction of negligible isospin asymmetry. The observation of the decay B0 → Ks0μ+μ- is reported with 5.7 σ significance. Assuming that the branching fraction of B0 → K0μ+μ- is twice that of B 0 → Ks0μ+μ-, the branching fractions of B0 → K0μ +μ- and B → K*+μ +μ- are found to be (0.31+0.07-0.06) × 10-6 and (1.16 ±0.19) × 10-6, respectively.

Abstract:

The decay mode Bs0 → Ds∓ K± allows for one of the theoretically cleanest measurements of the CKM angle γ through the study of time-dependent CP violation. This paper reports a measurement of its branching fraction relative to the Cabibbo-favoured mode Bs0 → Ds- π+ based on a data sample corresponding to 0.37 fb-1 of proton-proton collisions at √s = 7TeV collected in 2011 with the LHCb detector. In addition, the ratio of B meson production fractions fs=fd, determined from semileptonic decays, together with the known branching fraction of the control channel B0 → D-π+, is used to perform an absolute measurement of the branching fractions: B( Bs0 → D s- π+) = (2.95 ± 0.05 ± 0.17-0.22+0.18) × 10-3 ; B( B s0 → Ds∓ K ±) = (1.90 ± 0.12 ± 0.13-0.14+0.12) × 10-4 ; where the first uncertainty is statistical, the second the experimental systematic uncertainty, and the third the uncertainty due to fs=fd. Copyright CERN.