LHCb

Abstract:

A test of lepton universality, performed by measuring the ratio of the branching fractions of the B 0 → K *0 μ + μ − and B 0 → K *0 e + e − decays, RK*0, is presented. The K *0 meson is reconstructed in the final state K + π − , which is required to have an invariant mass within 100 MeV/c 2 of the known K * (892) 0 mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb −1 , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q 2 , to be (Formula presented.) The corresponding 95.4% confidence level intervals are [0.52, 0.89] and [0.53, 0.94] . The results, which represent the most precise measurements of RK*0 to date, are compatible with the Standard Model expectations at the level of 2.1–2.3 and 2.4–2.5 standard deviations in the two q 2 regions, respectively.[Figure not available: see fulltext.].

Abstract:

The first observation of the decays $Λ_{b}^{0}→χ_{c1}pK^{-}$ and $Λ_{b}^{0}→χ_{c2}pK^{-}$ is reported using a data sample corresponding to an integrated luminosity of $3.0  fb^{-1}$, collected by the LHCb experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured:

$B(Λ_{b}^{0}→χ_{c1}pK^{-})/B(Λ_{b}^{0}→J/ψpK^{-})=0.242±0.014±0.013±0.009,$ $B(Λ_{b}^{0}→χ_{c2}pK^{-})/B(Λ_{b}^{0}→J/ψpK^{-})=0.248±0.020±0.014±0.009,$ $B(Λ_{b}^{0}→χ_{c2}pK^{-})/B(Λ_{b}^{0}→χ_{c1}pK^{-})=1.02±0.10±0.02±0.05,$

where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the $χ_{c1}→J/ψγ$ and $χ_{c2}→J/ψγ$ decays. Using both decay modes, the mass of the $Λ_{b}^{0}$ baryon is also measured to be $m_{Λ_{b}^{0}}=5619.44±0.28±0.26  MeV/c^{2}$, where the first and second uncertainties are statistical and systematic, respectively.

Abstract:

The decays of $B_s^0$ and $\overline{B}_s^0$ mesons into the $J/\psi K^+K^-$ final state are studied in the $K^+K^-$ mass region above the $\phi(1020)$ meson in order to determine the resonant substructure and measure the $CP$-violating phase, $\phi_s$, the decay width, $\Gamma_s$, and the width difference between light and heavy mass eigenstates, $\Delta\Gamma_s$. A decay-time dependent amplitude analysis is employed. The data sample corresponds to an integrated luminosity of $3{\rm fb}^{-1}$ produced in 7 and 8 Tev $pp$ collisions at the LHC, collected by the LHCb experiment. The measurement determines $\phi_s = 119\pm107\pm34 {\rm \, mrad}$. A combination with previous LHCb measurements using similar decays into the $J/\psi \pi^+\pi^-$ and $J/\psi\phi(1020)$ final states gives $\phi_s=1\pm37 {\rm \,mrad}$, consistent with the Standard Model prediction.