Measurement of the decay width di ff erence ΔΓ s and the CP-violating phase φ s in B s → J /ψφ (1020) decays at CMS

The CP-violating weak phase φ s and the decay width di ff erence ΔΓ s of B s mesons are measured by the CMS experiment at the LHC using a data sample of B s → J /ψ ( μ + μ − ) φ (K + K − ) decays. The analysed dataset corresponds to an integrated luminosity of about 20 fb − 1 collected in pp collisions at a centre-of-mass energy √ s = 8 TeV. A total of 49 000 reconstructed B s decays are used to extract the values 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 . 03 ± 0 . 11 (stat . ) ± 0 . 03 (syst . ) rad, and the decay width di ff erence between the B s mass eigenstates is ΔΓ s = 0 . 096 ± 0 . 014 (stat . ) ± 0 . 007 (syst . ) ps − 1 .