Measurement of the CP-violating phase $ϕ_s$ and the $B^0_s$ meson decay width difference with $B^0_s \to J/ψϕ$ decays in ATLAS

Abstract

A measurement of the $B^0_s$ decay parameters in the $B^0_s \to J/ψϕ$ channel using an integrated luminosity of 14.3 $\mathrm{fb}^{-1}$ 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 $\mathrm{fb}^{-1}$ of 7 TeV data, leading to the following: \begin{eqnarray*} ϕ_s & = & -0.090 \pm 0.078\;\mathrm{(stat.)} \pm 0.041\;\mathrm{(syst.)\;rad} \\ ΔΓ_s & = & 0.085 \pm 0.011\;\mathrm{(stat.)} \pm 0.007\;\mathrm{(syst.)\;ps}^{-1} \\ Γ_s & = & 0.675 \pm 0.003\;\mathrm{(stat.)} \pm 0.003\;\mathrm{(syst.)\;ps}^{-1}. \end{eqnarray*} 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.