Measurement of the time-dependent CP asymmetries in B s 0 → J/ψK S 0

The first measurement of decay-time-dependent CP asymmetries in the decay B0 s → J/ψK0 S and an updated measurement of the ratio of branching fractions B(B0 s → J/ψK0 S )/B(B0 → J/ψK0 S ) are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fb−1 of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The results on the CP asymmetries are A∆Γ(B 0 s → J/ψK0 S ) = 0.49 ± 0.77 0.65 (stat) ± 0.06(syst), Cdir(B 0 s → J/ψK0 S ) = −0.28 ± 0.41(stat) ± 0.08(syst), Smix(B 0 s → J/ψK0 S ) = −0.08 ± 0.40(stat) ± 0.08(syst). The ratio B(B0 s → J/ψK0 S )/B(B0 → J/ψK0 S ) is measured to be 0.0431 ± 0.0017(stat) ± 0.0012(syst) ± 0.0025(fs/fd), where the last uncertainty is due to the knowledge of the B0 s and B0 production fractions.