Observation of B0s –B¯¯¯¯0s mixing and measurement of mixing frequencies using semileptonic B decays

Abstract

The B0s and B 0 mixing frequencies, Δm s and Δm d , are measured using a data sample corresponding to an integrated luminosity of 1.0 fb−1 collected by the LHCb experiment in pp collisions at a centre of mass energy of 7 TeV during 2011. Around 1.8×106 candidate events are selected of the type B0(s)→D−(s)μ+ (+ anything), where about half are from peaking and combinatorial backgrounds. To determine the B decay times, a correction is required for the momentum carried by missing particles, which is performed using a simulation-based statistical method. Associated production of muons or mesons allows us to tag the initial-state flavour and so to resolve oscillations due to mixing.