First evidence for mixing-induced CP violation in B0s -> J/psi phi(1020) decays in pp collisions at sqrt(s) = 13 TeV

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 B0s → J=ψϕð1020Þ decays from pp collisions at ffiffis p ¼ 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 μþμ−KþK− final state, consistent with a ϕð1020Þ → KþK− decay, is used to measure parameters of the B0s − B¯ 0s system. The weak phase is measured to be ϕs¼−7322ðstatÞ10ðsystÞmrad, which, combined with the ffiffis p ¼ 8 TeV CMS result, gives ϕs ¼ −75 23 mrad. This value differs from zero by 3.2 standard deviations, providing the first evidence for mixing-induced CP violation in B0 s → J=ψϕð1020Þ decays. All measured physics parameters are found to agree with standard model predictions where available.