Time-dependent angular analysis of the decay Bₛ⁰→ J / ψ φ . and extraction of ΔΓ s and the CP-violating weak phase ϕ s by ATLAS

A bstract A measurement of Bₛ⁰→ J / ψ φ . 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 ∥ (0)| 2 are also measured. The values reported for these parameters are: $ {array}{*{20}{c}} {{φ_s}=0.22 ± 0.41\ ( {stat.} ) ± 0.10\ ( {syst.} )\ rad} \\ { {_s}=0.053 ± 0.021\ ( {stat.} ) ± 0.010\ ( {syst.} )\ p{{s}⁻¹}} \\ {{_s}=0.677 ± 0.007\ ( {stat.} ) ± 0.004\ ( {syst.} )\ p{{s}⁻¹}} \\ {|{A_0}(0){|^2} = 0.528 ± 0.006\ ( {stat.} ) ± 0.009\ ( {syst.} )} \\ {|{A∥}(0){|^2} = 0.220 ± 0.008\ ( {stat.} ) ± 0.007\ ( {syst.} )} \\ {array} $ 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 Bₛ⁰→ J / ψ K⁺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.