LHCb

Abstract:

Time-dependent CPviolation is measured in the B0→J/Ψπ+π-channel for each π+π-resonant final state using data collected with an integrated luminosity of 3.0fb-1in ppcollisions using the LHCb detector. The final state with the largest rate, J/Ψρ0(770), is used to measure the CP-violating angle 2βeffto be (41.7 ±9.6+2.8-6.3)°. This result can be used to limit the size of penguin amplitude contributions to CPviolation measurements in, for example, B0s→J/Ψϕdecays. Assuming approximate SU(3) flavour symmetry and neglecting higher order diagrams, the shift in the CP-violating phase ϕsis limited to be within the interval [-1.05°, +1.18°] at 95% confidence level. Changes to the limit due to SU(3) symmetry breaking effects are also discussed.

Abstract:

Abstract: The associated production of a Z boson or an off-shell photon γ* with a bottom quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy of 7 TeV. The Z bosons are reconstructed in the Z/γ* → μ+μ− final state from muons with a transverse momentum larger than 20 GeV, while two transverse momentum thresholds are considered for jets (10 GeV and 20 GeV). Both muons and jets are reconstructed in the pseudorapidity range 2.0 < η < 4.5. The results are based on data corresponding to 1.0 fb−1 recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet cross-section is normalized to the Z+jet cross-section. The measured cross-sections are(Formula presented.)for pT(jet) > 10 GeV, and(Formula presented.)for pT(jet) > 20 GeV.[Figure not available: see fulltext.].

Abstract:

Abstract: A search for the lepton flavour violating decay τ− → μ−μ+μ− is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of 1.0 fb−1 of proton-proton collisions at a centre-of-mass energy of 7 TeV and 2.0 fb−1 at 8 TeV. No evidence is found for a signal, and a limit is set at 90% confidence level on the branching fraction, B(τ− → μ−μ+μ−) < 4.6 × 10−8

Abstract:

© 2015 The Authors. A search for the rare decays B⁰s → π⁺π^-μ⁺μ^- and B⁰ → π⁺π^-μ⁺μ^- is performed in a data set corresponding to an integrated luminosity of 3.0fb^-1collected by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7 and 8TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5-1.3GeV/c² and with muon pairs that do not originate from a resonance are considered. The first observation of the decay B⁰s → π⁺π^-μ⁺μ^-and the first evidence of the decay B⁰ → π⁺π^-μ⁺μ^-are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be B(B⁰s → π⁺pπμ⁺μ^-) =(8.6 ±1.5(stat) ±0.7(syst) ±0.7 (norm)) ×10^-8 and B(B⁰ → π⁺π^-μ⁺μ^-) =(2.11±0.51(stat)±0.15(syst)±0.16(norm)) × 10^-8, where the third uncertainty is due to the branching fraction of the decay B⁰ → J/ψ(→ μ⁺μ^-)K*(892)⁰(→ K⁺p^-), used as a normalisation.

Abstract:

© 2015, The Author(s). Abstract: A study of B and B^s meson decays into J/ψ η and J/ψ η^′ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fb⁻¹ of integrated luminosity. The decay B⁰ → J/ψ η^′ is observed for the first time. The following ratios of branching fractions are measured: (Formula Presented) where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a B^s or a B⁰ meson. The branching fraction ratios are used to determine the parameters of η − η^′ meson mixing. In addition, the first evidence for the decay B^s → ψ(2S)η^′ is reported, and the relative branching fraction is measured, (Formula Presented) where the third uncertainty is due to the limited knowledge of the branching fractions of J/ψ and ψ(2S) mesons.