Measurement of the CP-violating phase ϕ_s and the B⁰_s meson decay width difference with B⁰_s → J/ψϕ decays in ATLAS

A measurement of the B⁰_s decay parameters in the B⁰_s → J/ψϕ channel using an integrated luminosity of 14.3 fb⁻¹ collected by the ATLAS detector from 8 TeV pp collisions at the LHC is presented. The measured parameters include the CP-violating phase ϕ_s, the decay width Γ_s and the width difference between the mass eigenstates ΔΓ_s. The values measured for the physical parameters are statistically combined with those from 4.9 fb⁻¹ of 7 TeV data, leading to the following:

ϕ_s = −0.090 ± 0.078(stat.) ± 0.041(syst.) rad
ΔΓ_s = 0.085 ± 0.011(stat.) ± 0.007(syst.) ps⁻¹

Γ_s = 0.675 ± 0.003(stat.) ± 0.003(syst.) ps⁻¹.

In the analysis the parameter ΔΓ_s is constrained to be positive. Results for ϕ_s and ΔΓ_s are also presented as 68% and 95% likelihood contours in the ϕ_s−ΔΓ_s plane. Also measured in this decay channel are the transversity amplitudes and corresponding strong phases. All measurements are in agreement with the Standard Model predictions.