Measurement of the CP-violating phase β_{s}^{J/ψφ} in B_{s}^{0}→J/ψφ decays with the CDF II detector

We present a measurement of the CP-violating parameter βJ/ψφs using approximately 6500 B0s→J/ψφ decays reconstructed with the CDF II detector in a sample of pp ̄ collisions at √s=1.96 TeV corresponding to 5.2 fb−1 integrated luminosity produced by the Tevatron collider at Fermilab. We find the CP-violating phase to be within the range βJ/ψφs∈[0.02,0.52]∪[1.08,1.55] at 68% confidence level where the coverage property of the quoted interval is guaranteed using a frequentist statistical analysis. This result is in agreement with the standard model expectation at the level of about one Gaussian standard deviation. We consider the inclusion of a potential S-wave contribution to the B0s→J/ψK+K− final state which is found to be negligible over the mass interval 1.009<m(K+K−)<1.028 GeV/c2. Assuming the standard model prediction for the CP-violating phase βJ/ψφs, we find the B0s decay width difference to be ΔΓs=0.075±0.035(stat)±0.006(syst) ps−1. We also present the most precise measurements of the B0s mean lifetime τ(B0s)=1.529±0.025(stat)±0.012(syst) ps, the polarization fractions |A0(0)|2=0.524±0.013(stat)±0.015(syst) and |A∥(0)|2=0.231±0.014(stat)±0.015(syst), as well as the strong phase δ⊥=2.95±0.64(stat)±0.07(syst) rad. In addition, we report an alternative Bayesian analysis that gives results consistent with the frequentist approach.