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

See paper for full list of authors – 26 pages plus author list (43 pages total), 10 figures, 8 tables, submitted to JHEP, all figures and tables are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2014-03/International audienceA measurement of the $B^0_s$ decay parameters in the $B^0_s \to J/\psi\phi$ 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 $\phi_s$, the decay width $\Gamma_s$ and the width difference between the mass eigenstates $\Delta\Gamma_s$. 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*} \phi_s & = & -0.098 \pm 0.084\;\mathrm{(stat.)} \pm 0.040\;\mathrm{(syst.)\;rad} \\ \Delta\Gamma_s & = & 0.083 \pm 0.011\;\mathrm{(stat.)} \pm 0.007\;\mathrm{(syst.)\;ps}^{-1} \\ \Gamma_s & = & 0.677 \pm 0.003\;\mathrm{(stat.)} \pm 0.003\;\mathrm{(syst.)\;ps}^{-1}. \end{eqnarray*} In the analysis the parameter $\Delta\Gamma_s$ is constrained to be positive. Results for $\phi_s$ and $\Delta\Gamma_s$ are also presented as 68% and 95% likelihood contours in the $\phi_s$-$\Delta\Gamma_s$ 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