Measurement of the CP-violating phase βsJ/ψϕ in Bs0→J/ψϕ decays with the CDF II detector

Abstract

We present a measurement of the CP-violating parameter βsJ/ψϕ using approximately 6500 Bs0→J/ψϕ decays reconstructed with the CDF II detector in a sample of pp̅ 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 βsJ/ψϕ∈[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 Bs0→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 βsJ/ψϕ, we find the Bs0 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 Bs0 mean lifetime τ(Bs0)=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.