Measurement of the effective Bs0→J/ψKS0 lifetime

Abstract This paper reports the first measurement of the effective B s 0 → J / ψ 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: τ J / ψ K S 0 eff = 1.75 ± 0.12 ( stat ) ± 0.07 ( syst ) ps and B ( B s 0 → J / ψ K S 0 ) = ( 1.97 ± 0.23 ) × 10 − 5 . For the latter measurement, the uncertainty includes both statistical and systematic sources.