Measurement of the CP-Violating Phase ϕs in the Decay B0s→J/ψϕ

Abstract

We present a measurement of the time-dependent C P -violating asymmetry in B 0 s → J / ψ ϕ decays, using data collected with the LHCb detector at the LHC. The decay time distribution of B 0 s → J / ψ ϕ is characterized by the decay widths Γ H and Γ L of the heavy and light mass eigenstates, respectively, of the B 0 s − ¯¯¯ B 0 s system and by a C P -violating phase ϕ s . In a sample of about 8500 B 0 s → J / ψ ϕ events isolated from 0.37 fb − 1 of p p collisions at √ s = 7 TeV , we measure ϕ s = 0.15 ± 0.18 ( stat ) ± 0.06 ( syst ) rad . We also find an average B 0 s decay width Γ s ≡ ( Γ L + Γ H ) / 2 = 0.657 ± 0.009 ( stat ) ± 0.008 ( syst ) ps − 1 and a decay width difference Δ Γ s ≡ Γ L − Γ H = 0.123 ± 0.029 ( stat ) ± 0.011 ( syst ) ps − 1 . Our measurement is insensitive to the transformation ( ϕ s , Δ Γ s ) ↦ ( π − ϕ s , − Δ Γ s ) .