Measurement of the $CP$-violating phase ${\varphi }_s$ in $B_s^0\to J/\psi \varphi$ decays in ATLAS at 13 TeV

Abstract

A measurement of the $B_s^0\to J/\psi \varphi$ decay parameters using 80.5 ${\mathrm{fb}}^{-1}$ 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 ${\varphi }_s$, the width difference $\Delta {\Gamma }_s$ between the $B_s^0$ meson mass eigenstates and the average decay width ${\Gamma }_s$. The values measured for the physical parameters are combined with those from 19.2 ${\mathrm{fb}}^{-1}$ of 7 TeV and 8 TeV data, leading to the following: \begin{eqnarray*} ϕ_s & = & -0.087\phantom{0} \pm 0.036\phantom{0} ~\mathrm{(stat.)} \pm 0.021\phantom{0} ~\mathrm{(syst.)~rad} \\ ΔΓ_{s} & = & \phantom{-}0.0657 \pm 0.0043 ~\mathrm{(stat.)} \pm 0.0037 ~\mathrm{(syst.)~ps}^{-1} \\ Γ_{s} & = & \phantom{-}0.6703 \pm 0.0014 ~\mathrm{(stat.)} \pm 0.0018 ~\mathrm{(syst.)~ps}^{-1} \\ \end{eqnarray*} Results for ${\varphi }_s$ and $\Delta {\Gamma }_s$ are also presented as 68% confidence level contours in the ${\varphi }_s$-$\Delta {\Gamma }_s$ plane. Furthermore, the transversity amplitudes and corresponding strong phases are measured. ${\varphi }_s$ and $\Delta {\Gamma }_s$ measurements are in agreement with the Standard Model predictions.

51 pages in total, author list starting page 35, 12 figures, 11 tables. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2018-01/

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