Measurement of the CP-violating weak phase φ_s and the decay width difference Δ⌈_s using the Bº_s →J/ψφ(1020) decay channel in pp collisions at √s=8 TeV

The CP-violating weak phase φ s of the Bs0 meson and the decay width difference δΓ s of the Bs0 light and heavy mass eigenstates are measured with the CMS detector at the LHC using a data sample of Bs0→J/ψφ(1020)→μ+μ-K+K- decays. The analysed data set corresponds to an integrated luminosity of 19.7fb -1 collected in pp collisions at a centre-of-mass energy of 8TeV. A total of 49 200 reconstructed Bs0 decays are used to extract the values of φ s and δΓ s by performing a time-dependent and flavour-tagged angular analysis of the μ + μ - K + K - final state. The weak phase is measured to be φ s =-0.075±0.097(stat)±0.031(syst) rad, and the decay width difference is δΓ s =0.095±0.013(stat)±0.007(syst) ps -1 .