Tagged time-dependent angular analysis of Bs→J/ψϕ decays with 337~pb−1 at LHCb

Abstract

The interference between Bs decays to J/ψϕ either directly or via Bs−B¯¯¯¯s oscillation gives rise to a CP violating phase ϕJψϕs. Using a sample of 8276±94 Bs→J/ψϕ events extracted from 337~pb−1 of pp collisions collected during the 2011 LHC run at s√=7~TeV, we fit for nine physics parameters, among which the phase ϕJψϕs, the decay width difference ΔΓs and the decay width Γs. For one of two ambiguous solutions (ϕJψϕs↔π−ϕJψϕs; ΔΓs↔−ΔΓs) we find ϕJψϕsΓsΔΓs===0.130.6560.123±±±0.180.0090.029(stat)(stat)(stat)±±±0.070.0080.011(syst)(syst)(syst)rad,ps−1,ps−1, in good agreement with the Standard Model predictions. This is the most precise measurement of ϕJψϕs and Γs. Furthermore, it is the first direct experimental evidence of a non-zero value of ΔΓs.