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

ATLAS Collaboration

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A 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 & = & -0.090 \pm 0.078\;\mathrm{(stat.)} \pm 0.041\;\mathrm{(syst.)\;rad} \\ \Delta\Gamma_s & = & 0.085 \pm 0.011\;\mathrm{(stat.)} \pm 0.007\;\mathrm{(syst.)\;ps}^{-1} \\ \Gamma_s & = & 0.675 \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.
Original languageEnglish
JournalJournal of High Energy Physics
Early online date24 Aug 2016
Publication statusE-pub ahead of print - 24 Aug 2016

Bibliographical note

27 pages plus author list (44 pages total), 10 figures, 8 tables, published version, all figures and tables are available at


  • hep-ex
  • B physics
  • Hadron-Hadron scattering (experiments)
  • CP violation
  • Flavor physics


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