Measurement of the CP-Violating Phase βsJ/ψϕ in Bs0→J/ψϕ decays with the CDF II Detector

We present a measurement of the CP-violating parameter J/s using approximately 6500 B0 s ! J/ decays reconstructed with the CDF II detector in a sample of p¯p collisions at ps = 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 J/ s 2 [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/ K+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 J/s , we find the B0s decay width difference to be s = 0.075 ± 0.035 (stat) ± 0.006 (syst) ps−1. We also present the most precise measurements of the B0s mean lifetime (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 |Ak(0)|2 = 0.231±0.014 (stat)±0.015 (syst), as well as the strong phase ⊥ = 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.