New Measurement of the Bs Mixing Phase at CDF

TL;DR

This paper reports a precise measurement of the Bs mixing phase and decay width difference using a large dataset, with improvements in analysis methods, providing results consistent with the Standard Model.

Contribution

The study introduces a fully data-driven flavor tagging calibration and accounts for S-wave contributions, enhancing measurement accuracy of Bs mixing parameters.

Findings

CP-violating phase range: [0.02, 0.52] U [1.08, 1.55] at 68% CL

Decay width difference: 0.075 +/- 0.035 (stat) +/- 0.01 (syst) 1/ps

Most precise Bs lifetime and polarization amplitudes reported

Abstract

The CDF collaboration presents an updated measurement of the CP-violating parameter beta_s and of the decay width difference Delta Gamma_s using approximately 6500 Bs to J/Psi Phi decays collected by the dimuon trigger and reconstructed in a data sample corresponding to 5.2/fb of integrated luminosity. Besides exploiting the two-fold increase in the data sample with respect to the previous measurement, several improvements have been introduced in the analysis including a fully data-driven flavor tagging calibration and proper treatment of possible S-wave contributions. We find that the CP-violating phase is within the range beta_s in [0.02, 0.52] U [1.08,1.55] at 68C.L. The Standard Model p-value is 0.31. The decay width difference is found to be Delta Gamma_s = 0.075 +/- 0.035 (stat) +/- 0.01 syst 1/ps. In addition, we present the most precise mean Bs lifetime tau_s, polarization amplitudes |A_0|^2, |A_{\parallel}|^2 and |A_{\perp}|^2, as well as strong phase delta_perp: tau_s = 458.6 +/- 7.6$ (stat) +/- 3.6 (syst) microns |A_0|^2 = 0.524 +/- 0.013 (stat) +/- 0.015 (syst) |A_{\parallel}|^2 = 0.231 +/- 0.014 (stat) +/- 0.015 (syst) delta_perp = 2.95 +/- 0.64 (stat) +/- 0.07 (syst).