Time-dependent angular analysis of the decay B⁰_s → J/ψφ and extraction of ΔΓ_s and the CP-violating weak phase φ_s by ATLAS

Abstract

A measurement of B⁰_s → J/ψϕ decay parameters, including the CP-violating weak phase ϕ_s and the decay width difference ΔΓ_s is reported, using 4.9 fb₋₁ of integrated luminosity collected in 2011 by the ATLAS detector from LHC pp collisions at a centre-of-mass energy √s = 7 TeV. The mean decay width Γ_s and the transversity amplitudes |A₀(0)|² and |A_∥(0)|² are also measured. The values reported for these parameters are: ϕ_s = 0.22 ± 0.41 (stat.) ± 0.10 (syst.) rad ΔΓ_s = 0.053 ± 0.021 (stat.) ± 0.010 (syst.) ps⁻¹ Γ_s = 0.677 ± 0.007 (stat.) ± 0.004 (syst.) ps⁻¹ |A₀(0)|² = 0.528 ± 0.006 (stat.) ± 0.009 (syst.) |A_∥(0)|² = 0.220 ± 0.008 (stat.) ± 0.007 (syst.) where the values quoted for ϕ_s and ΔΓ_s correspond to the solution compatible with the external measurements to which the strong phase δ⊥ is constrained and where ΔΓ_s is constrained to be positive. The fraction of S-wave KK or f₀ contamination through the decays Bsup>0</sup>_s → J/ψK+K− (f₀) is measured as well and is found to be consistent with zero. Results for ϕ_s and ΔΓ_s are also presented as 68%, 90% and 95% likelihood contours, which show agreement with Standard Model expectations.