Measurement of the CP-violating phase ${\varphi }_s$ and the $B_s^0$ meson decay width difference with $B_s^0\to J\mathrm{/}\psi \varphi$ decays in ATLAS

A measurement of the $B_s^0$ decay parameters in the $B_s^0\to J\mathrm{/}\psi \varphi$ channel using an integrated luminosity of 14.3 ${\mathrm{f}\mathrm{b}}^{-1}$ collected by the ATLAS detector from 8 TeV $pp$ collisions at the LHC is presented. The measured parameters include the $CP$-violating phase ${\varphi }_s$, the decay width ${\mathrm{\Gamma }}_s$ and the width difference between the mass eigenstates $\mathrm{\Delta }{\mathrm{\Gamma }}_s$. The values measured for the physical parameters are statistically combined with those from 4.9 ${\mathrm{f}\mathrm{b}}^{-1}$ of 7 TeV data, leading to the following: \begin{eqnarray*} \phi_s & = & -0.090 \pm 0.078;$(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})$ \pm 0.041;$(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})\mathrm{r}\mathrm{a}\mathrm{d}$ \ \Delta\Gamma_s & = & 0.085 \pm 0.011;$(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})$ \pm 0.007;$(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})\mathrm{p}\mathrm{s}$^{-1} \ \Gamma_s & = & 0.675 \pm 0.003;$(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})$ \pm 0.003;$(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})\mathrm{p}\mathrm{s}$^{-1}. \end{eqnarray*} In the analysis the parameter $\mathrm{\Delta }{\mathrm{\Gamma }}_s$ is constrained to be positive. Results for ${\varphi }_s$ and $\mathrm{\Delta }{\mathrm{\Gamma }}_s$ are also presented as 68% and 95% likelihood contours in the ${\varphi }_s-\mathrm{\Delta }{\mathrm{\Gamma }}_s$ 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.