A measurement of B0s → 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 |A 0(0)|2 and |A arap;(0)|2 are also measured. The values reported for these parameters are: φs = 0.22 ± 0.41 (stat) ± 0.10 (syst) rad} ΔΓ s = 0.053 ± 0.021 (stat) ± 0.010 (sast) ps-1 Γ s = 0.677 ± 0.007 (stat) ± 0.004 (sast) ps-1 |A0(0)|2 = 0.528 ± 0.006 (stat) ± 0.009 (sast) |A0(0)|2 = 0.220 ± 0.008 (stat) ± 0.007 (sast) 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 f 0 contamination through the decays B0s→ J /ψK + K-}}\left({{f-0}} \right)}} \right.} 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.[Figure not available: see fulltext.] © 2012 CERN for the benefit of the ATLAS collaboration.

Time-dependent angular analysis of the decay B⁰ₛ → J/ψφ and extraction of ΔΓₛ and the CP-violating weak phase φₛ by ATLAS