A search for the rare decays \(B^0_s\to\mu^+\mu^-\) and \(B^0\to\mu^+\mu^-\) is performed at the LHCb experiment using data collected in \(pp\) collisions corresponding to a total integrated ...luminosity of 4.4 fb\(^{-1}\). An excess of \(B^0_s\to\mu^+\mu^-\) decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be \({\cal B}(B^0_s\to\mu^+\mu^-)=\left(3.0\pm 0.6^{+0.3}_{-0.2}\right)\times 10^{-9}\), where the first uncertainty is statistical and the second systematic. The first measurement of the \(B^0_s\to\mu^+\mu^-\) effective lifetime, \(\tau(B^0_s\to\mu^+\mu^-)=2.04\pm 0.44\pm 0.05\) ps, is reported. No significant excess of \(B^0\to\mu^+\mu^-\) decays is found and a 95 % confidence level upper limit, \({\cal B}(B^0\to\mu^+\mu^-)<3.4\times 10^{-10}\), is determined. All results are in agreement with the Standard Model expectations.
The time-dependent CP asymmetry in B_s^0\to J/\psi K^+K^- decays is measured using \(pp\) collision data at \sqrt{s}=7TeV, corresponding to an integrated luminosity of 1.0fb^-1, collected with the ...LHCb detector. The decay time distribution is characterised by the decay widths \Gamma_L and \Gamma_H of the light and heavy mass eigenstates of the B_s^0--\bar{B}_s^0 system and by a CP-violating phase \phi_s. In a sample of 27\,617 B_s^0\to J/\psi K^+K^- decays, where the dominant contribution comes from B_s^0\to J/\psi\phi\ decays, these parameters are measured to be \phi_s = 0.07 \pm 0.09 (stat) \pm 0.01 (syst) rad, \Gamma_s \equiv (\Gamma_L+\Gamma_H)/2 = 0.663 \pm 0.005 (stat) \pm 0.006 (syst) ps^-1, \Delta\Gamma_s \equiv \Gamma_L -\Gamma_H = 0.100 \pm 0.016 (stat) \pm 0.003 (syst) & ps^-1, corresponding to the single most precise determination of \phi_s, \Delta\Gamma_s and \Gamma_s. The result of performing a combined analysis with B_s^{0} \to J/\psi \pi^+\pi^- decays gives \phi_s = 0.01 \pm 0.07 (stat) \pm 0.01 (syst) rad, \Gamma_s = 0.661 \pm 0.004 (stat) \pm 0.006 (syst) ps^-1, \Delta\Gamma_s = 0.106 \pm 0.011 (stat) \pm 0.007 (syst) & ps^-1. All measurements are in agreement with the Standard Model predictions.
Searches for the lepton flavour violating decay \(\tau^-\rightarrow \mu^-\mu^+\mu^-\) and the lepton flavour and baryon number violating decays \(\tau^-\rightarrow \bar{p}\mu^+\mu^-\) and ...\(\tau^-\rightarrow p\mu^-\mu^-\) have been carried out using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb\(^{-1}\), taken by the LHCb experiment at \(\sqrt{s} = 7\) TeV. No evidence has been found for any signal, and limits have been set at 90% confidence level on the branching fractions: \(\cal B(\tau^-\rightarrow \mu^-\mu^+\mu^-) < 8.0 \times 10^{-8}\), \(\cal B(\tau^-\rightarrow \bar{p}\mu^+\mu^-) < 3.3 \times 10^{-7}\) and \(\cal B(\tau^-\rightarrow p\mu^-\mu^-) < 4.4 \times 10^{-7}\). The results for the \(\tau^-\rightarrow \bar{p}\mu^+\mu^-\) and \(\tau^-\rightarrow p\mu^-\mu^-\) decay modes represent the first direct experimental limits on these channels.
An angular analysis of Lambda_b0 -> J/psi Lambda decays is performed using a data sample corresponding to 1.0 fb^{-1} collected in pp collisions at sqrt(s) = 7 TeV with the LHCb detector at the LHC. ...A parity violating asymmetry parameter characterising the Lambda_b0 -> J/psi Lambda decay of 0.05 +/- 0.17 +/- 0.07 and a Lambda_b0 transverse production polarisation of 0.06 +/- 0.07 +/- 0.02 are measured, where the first uncertainty is statistical and the second systematic.
Using pp collision data, corresponding to an integrated luminosity of \(1.0 \mathrm{fb}^{-1}\), collected by LHCb in 2011 at a center-of-mass energy of 7 TeV, we report the measurement of direct CP ...violation in \(B^0_s \to K^-\pi^+\) decays, \(A_{C/!P}(B^0_s \rightarrow K^- \pi^+)=0.27 \pm 0.04\,\mathrm{(stat)} \pm 0.01\,\mathrm{(syst)}\), with significance exceeding five standard deviations. This is the first observation of CP violation in the decays of \(B^0_s\) mesons. Furthermore, we provide an improved determination of direct CP violation in \(B^0 \to K^+\pi^-\) decays, \(A_{C/!P}(B^0\rightarrow K^+ \pi^-)=-0.080 \pm 0.007\,\mathrm{(stat)} \pm 0.003\,\mathrm{(syst)}\), which is the most precise measurement of this quantity to date.
The first observation of the decay Bs -> D0bar K- {\pi}+ is reported. The analysis is based on a data sample, corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions, collected with ...the LHCb detector. The branching fraction relative to that of the topologically similar decay B0 -> D0bar {\pi}+ {\pi}- is measured to be BR(Bs -> D0bar K- {\pi}+)/BR(B0 -> D0bar {\pi}+ {\pi}-) = 1.18 +- 0.05 (stat.) +- 0.12 (syst.). In addition, the relative branching fraction of the decay B0 -> D0bar K+ {\pi}- is measured to be BR(B0 -> D0bar K+ {\pi}-)/BR(B0 -> D0bar {\pi}+ {\pi}-) = 0.106 +- 0.007 (stat.) +- 0.008 (syst.).
A search for direct CP violation in D0 -> h- h+ (where h=K or pi) is presented using data corresponding to an integrated luminosity of 1.0 fb^-1 collected in 2011 by LHCb in pp collisions at a ...centre-of-mass energy of 7 TeV. The analysis uses D0 mesons produced in inclusive semileptonic b-hadron decays to the D0 mu X final state, where the charge of the accompanying muon is used to tag the flavour of the D0 meson. The difference in the CP-violating asymmetries between the two decay channels is measured to be Delta A_CP = A_CP(K-K+) - A_CP(pi-pi+) = (0.49 +- 0.30 (stat) +- 0.14 (syst)) % . This result does not confirm the evidence for direct CP violation in the charm sector reported in other analyses.
This paper reports the first measurement of the effective B_s^0 -> J/{\psi} K_S^0 lifetime and an updated measurement of its time-integrated branching fraction. Both measurements are performed with a ...data sample, corresponding to an integrated luminosity of 1.0 fb^{-1} of pp collisions, recorded by the LHCb experiment in 2011 at a centre-of-mass energy of 7 TeV. The results are: tau_J/{\psi}K_S^0 = 1.75 +/- 0.12 (stat) +/- 0.07 (syst) and BR(B_s^0 -> J/{\psi} K_S^0) = (1.97 +/- 0.23) X 10^{-5}. For the latter measurement, the uncertainty includes both statistical and systematic sources.
Production cross-sections of prompt charm mesons are measured with the first data from \(pp\) collisions at the LHC at a centre-of-mass energy of \(13\,\mathrm{TeV}\). The data sample corresponds to ...an integrated luminosity of \(4.98 \pm 0.19\,\mathrm{pb}^{-1}\) collected by the LHCb experiment. The production cross-sections of \(D^{0}\), \(D^{+}\), \(D_{s}^{+}\), and \(D^{*+}\) mesons are measured in bins of charm meson transverse momentum, \(p_{\mathrm{T}}\), and rapidity, \(y\), and cover the range \(0 < p_{\mathrm{T}} < 15\,\mathrm{GeV}/c\) and \(2.0 < y < 4.5\). The inclusive cross-sections for the four mesons, including charge conjugation, within the range of \(1 < p_{\mathrm{T}} < 8\,\mathrm{GeV}/c\) are found to be \begin{equation} \sigma(pp \to D^{0} X) = 2072 \pm 2 \pm 124\,\mu\mathrm{b}\\ \sigma(pp \to D^{+} X) = 834 \pm 2 \pm \phantom{1}78\,\mu\mathrm{b}\\ \sigma(pp \to D_{s}^{+} X) = 353 \pm 9 \pm \phantom{1}76\,\mu\mathrm{b}\\ \sigma(pp \to D^{*+} X) = 784 \pm 4 \pm \phantom{1}87\,\mu\mathrm{b} \end{equation} where the uncertainties are due to statistical and systematic uncertainties, respectively.
The energy flow created in pp collisions at sqrt(s)=7 TeV is studied within the pseudorapidity range 1.9<eta<4.9 with data collected by the LHCb experiment. The measurements are performed for ...inclusive minimum-bias interactions, hard scattering processes and events with an enhanced or suppressed diffractive contribution. The results are compared to predictions given by PYTHIA-based and cosmic-ray event generators, which provide different models of soft hadronic interactions.
