Malcolm John

Abstract:

The relative rates of B-meson decays into J/ψ and ψ(2S) mesons are measured for the three decay modes in pp collisions recorded with the LHCb detector. The ratios of branching fractions (B) are measured to be B(B⁺ → ψ(2S)K⁺)/B(B⁺ → J/ψK⁺) = 0.594 ± 0.006(stat) ± 0.016(syst) ± 0.015(Rψ), B(B⁰ → ψ(2S)K*⁰)/B(B⁰ → J/ψK*⁰) = 0.476 ± 0.014(stat) ± 0.010(syst) ± 0.012(Rψ), B(B⁰s →ψ(2S)φ)/B(B⁰s →J/ψφ) = 0.489 ± 0.026(stat) ± 0.021(syst) ± 0.012(Rψ), where the third uncertainty is from the ratio of the ψ(2S) and J/ψ branching fractions to μ⁺ μ⁻.

Abstract:

During 2011 the LHCb experiment at CERN collected 1.0 fb-1 of sqrt{s} = 7 TeV pp collisions. Due to the large heavy quark production cross-sections, these data provide unprecedented samples of heavy flavoured hadrons. The first results from LHCb have made a significant impact on the flavour physics landscape and have definitively proved the concept of a dedicated experiment in the forward region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.

Abstract:

The prompt production of the charmonium χ c1 and χ c2 mesons has been studied in proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of s=7 TeV. The χ c mesons are identified through their decays χ c→J/ψγ with J/ψ→μ +μ - using 36 pb -1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two χ c spin states, σ(χ c2)/σ(χ c1), has been determined as a function of the J/ψ transverse momentum, pTJ/ψ, in the range from 2 to 15 GeV/c. The results are in agreement with the next-to-leading order non-relativistic QCD model at high pTJ/ψ and lie consistently above the pure leading-order colour-singlet prediction. © 2012 CERN.

Abstract:

The differential cross-section for the inclusive production of ψ(2S) mesons in pp collisions at √s = 7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated luminosity of 36 pb−1. The ψ(2S) mesons are reconstructed in the decay channels ψ(2S)→μ + μ − and ψ(2S)→J/ψπ + π −, with the J/ψ meson decaying into two muons. Results are presented both for promptly produced ψ(2S) mesons and for those originating from b-hadron decays. In the kinematic range pT(ψ(2S)) ≤ 16 GeV/c and 2 < y(ψ(2S)) ≤ 4.5 we measure σprompt(ψ(2S)) = 1.44 ± 0.01 (stat) ± 0.12 (syst) +0.20−0.40 (pol) μb, σb(ψ(2S)) = 0.25 ± 0.01 (stat) ± 0.02 (syst) μb, where the last uncertainty on the prompt cross-section is due to the unknown ψ(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/ψ measurements we determine the inclusive branching fraction B(b→ψ(2S)X) = (2.73 ± 0.06 (stat) ± 0.16 (syst) ± 0.24 (BF)) × 10−3, where the last uncertainty is due to the B(b → J/ψX), B(J/ψ →μ + μ −) and B(ψ(2S)→e + e −) branching fraction uncertainties.

Abstract:

A search for the decay $B^0_s\rightarrow J/\psi K^{*0}$ with $K^{*0} \rightarrow K^-\pi^+$ is performed with 0.37 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 7 TeV collected by the LHCb experiment, finding a $\Bs \to J\psi K^-\pi^+$ peak of $114 \pm 11$ signal events. The $K^-\pi^+$ mass spectrum of the candidates in the $B^0_s$ peak is dominated by the $K^{*0}$ contribution. Subtracting the non-resonant $K^-\pi^+$ component, the branching fraction of \BsJpsiKst is $(4.4_{-0.4}^{+0.5} \pm 0.8) \times 10^{-5}$, where the first uncertainty is statistical and the second systematic. A fit to the angular distribution of the decay products yields the \Kst polarization fractions $f_L = 0.50 \pm 0.08 \pm 0.02$ and $f_{||} = 0.19^{+0.10}_{-0.08} \pm 0.02$.