First Evidence for Mixing-Induced 𝐶�⁢𝑃� Violation in 𝐵�0 𝑠� →𝐽�/𝜓�⁢𝜙�⁡(1020) Decays in 𝑝�⁢𝑝� 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 𝐵0𝑠 →𝐽/𝜓⁢𝜙⁡(1020) decays from 𝑝⁢𝑝 collisions at √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 𝜇+⁢𝜇−⁢𝐾+⁢𝐾− final state, consistent with a 𝜙⁡(1020)→𝐾+⁢𝐾− decay, is used to measure parameters of the 𝐵0𝑠 −¯𝐵0𝑠 system. The weak phase is measured to be 𝜙s=−73±22⁢(stat)±10⁢(syst) mrad, which, combined with the √𝑠=8 TeV CMS result, gives 𝜙s=−75±23 mrad. This value differs from zero by 3.2 standard deviations, providing the first evidence for mixing-induced 𝐶⁢𝑃 violation in 𝐵0𝑠 →𝐽/𝜓⁢𝜙⁡(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.