Measurement of the CP Violating Phase Beta_s in B_s-]J/psi Phi Decays

Book excerpt: The CP violating phase [beta] j/[Psi][Phi]s is measured in decays of B0s → J/[Psi][Phi]. This measurement uses 5.2 fb-1 of data collected in √s = 1.96 TeV p$\bar{p}$ collisions at the Fermilab Tevatron with the CDF Run-II detector. CP violation in the Bs0-$\bar{B}$s0 system is predicted to be very small in the Standard Model. However, several theories beyond the Standard Model allow enhancements to this quantity by heavier, New Physics particles entering second order weak mixing box diagrams. Previous measurements have hinted at a deviation from the Standard Model expectation value for [beta]sJ/[Psi][Phi] with a significance of approximately 2[sigma]. The measurement described in this thesis uses the highest statistics sample available to date in the Bs0 → J/[Psi][Phi] decay channel, where J/[Psi] → [mu]+[mu]- and [Phi] → K+K-. Furthermore, it contains several improvements over previous analyses, such as enhanced signal selection, fully calibrated particle ID and flavour tagging, and the inclusion of an additional decay component in the likelihood function. The added decay component considers S-wave states of KK pairs in the Bs0 → J/[Psi] K+K- channel. The results are presented as 2-dimensional frequentist confidence regions for [beta]sJ/[Psi][Phi] and [Delta][Gamma] (the width difference between the Bs0 mass eigenstates), and as a confidence interval for [beta]sJ/[Psi][Phi] of [0.02,0.52] U [1.08, 1.55] at the 68% confidence level. The measurement of the CP violating phase obtained in this thesis is complemented by the world's most precise measurement of the lifetime [tau]s = 1.53 ± 0.025 (stat.) ± 0.012 (syst.) ps and decay width difference [Delta][Gamma] = 0.075 ± 0.035 (stat.) ± 0.01 (syst.) ps-1 of the Bs0 meson, with the assumption of no CP violation.