Measurement of the CP-violating phase φs in B⁰_s→ J/ψφ decays in ATLAS at 13 TeV

A measurement of the B⁰_s→J/ψΦ decay parameters using 80.5fb⁻¹ of integrated luminosity collected with the ATLAS detector from 13 TeV proton–proton collisions at the LHC is presented. The measured parameters include the CP-violating phase Φs, the width difference ΔΓ_s between the B⁰_s meson mass eigenstates and the average decay width Γ_s. The values measured for the physical parameters are combined with those from 19.2fb⁻¹ of 7 and 8 TeV data, leading to the following:

Φ _s =−0.087±0.036 (stat.)±0.021 (syst.) rad
ΔΓ_s =0.0657±0.0043 (stat.)±0.0037 (syst.) ps^-1
Γ_s =0.6703±0.0014 (stat.)±0.0018 (syst.) ps⁻¹

Results for Φ_s and ΔΓ_s are also presented as 68% confidence level contours in the Φ_s–ΔΓ_s plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. Φ_s and ΔΓ_s measurements are in agreement with the Standard Model predictions.