LHCb

Abstract:

A study of the decay $D^{0}\rightarrow K^{-}\pi^{+}\mu^{+}\mu^{-}$ is performed using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb$^{-1}$. Decay candidates with muon pairs that have an invariant mass in the range 675--875 MeV$/c^2$ are considered. This region is dominated by the $\rho^{0}$ and $\omega$ resonances. The branching fraction in this range is measured to be ${\cal B}$($D^{0}\rightarrow K^{-}\pi^{+}\mu^{+}\mu^{-}$ ) = $( 4.17 \pm 0.12(stat) \pm 0.40(syst) )\times10^{-6}$. This is the first observation of the decay $D^{0}\rightarrow K^{-}\pi^{+}\mu^{+}\mu^{-}$. Its branching fraction is consistent with the value expected in the Standard Model.

Abstract:

© 2016 The Authors.Measurements of the coherence factor RK3π, the average strong-phase difference δDK3π and mean amplitude ratio rDK3π for the decay D→K-π+π+π- are presented. These parameters are important inputs to the determination of the unitarity triangle angle γ in B-→DK- decays, where D designates a superposition of D0 and D-0 mesons decaying to a common final state. The results are based on a combined fit to observables obtained from a re-analysis of the CLEO-c ψ(3770) data set and those measured in a D0D-0 mixing study performed by the LHCb Collaboration.

Abstract:

Charm meson oscillations are observed in a time-dependent analysis of the ratio of D⁰ → K⁺π⁻π⁺π⁻ to D⁰ → K⁻π⁺π⁻π⁺ decay rates, using data corresponding to an integrated luminosity of 3.0  fb^⁻1 recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favored amplitudes rDK3π and the product of the coherence factor RDK3π and a charm mixing parameter y'K3π. The constraints measured are rDK3π=(5.67±0.12)×10^-2, which is the most precise determination to date, and RDK3π . y'K3π=(0.3 ± 1.8) × 10^-3, which provides useful input for determinations of the CP-violating phase γ in B^± → DK^±, D → K∓π^±π^∓π^± decays. The analysis also gives the most precise measurement of the D⁰ → K⁺π⁻π⁺π⁻ branching fraction, and the first observation of D0 - D0 oscillations in this decay mode, with a significance of 8.2 standard deviations.

Abstract:

Measurements of CP observables in B± → DK± and B± → Dπ± decays are presented where the D meson is reconstructed in the final states K±π∓, π±K∓, K+K−, π+π−, K±π∓π+π−, π±K∓π+π− and π+π−π+π−. This analysis uses a sample of charged B mesons from pp collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb^−1. Various CP-violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle γ. The analysis of the four-pion D decay mode is the first of its kind.

Abstract:

A search for the decays of the B+c meson to ppπ+ is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb-1 collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV. No signal is found and an upper limit, at 95% confidence level, is set, fc/fu × B(B+c → ppπ+) < 3.6×10^-8 in the kinematic region m(pp) < 2.85 GeV/c^2, pT(B) < 20 GeV/c and 2.0 < y(B) < 4.5, where B is the branching fraction and fc(fu) is the fragmentation fraction of the b quark into a Bc+ (B+) meson.