First Evidence for Mixing-Induced CP Violation in Bs0 → J/ψφ(1020) Decays in pp Collisions at √s=13 TeV

Abstract

A novel machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27 500 tagged B-s(0) -> J/psi phi(1020) decays from pp collisions at root s = 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb-1. A time- and flavor-dependent angular analysis of the mu(+)mu-K+K- final state, consistent with a phi(1020) -> K+K- decay, is used to measure parameters of the B-s(0) - (B) over bar (0)(s) system. The weak phase is measured to be phi(s) = - 73 +/- 22(stat) +/- 10(syst) mrad, which, combined with the root s = 8 TeV CMS result, gives phi(s) = - 75 +/- 23 mrad. This value differs from zero by 3.2 standard deviations, providing the first evidence for mixing-induced CP violation in B-s(0) -> J/psi phi(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.