Measurement of the decay width difference $\Delta \Gamma_s$ and the CP-violating phase $\phi_s$ in $B_s \to J/\psi \phi(1020)$ decays at CMS

The CP-violating weak phase ϕs and the decay width difference $ΔΓ_s$ of $B_s$ mesons are measured by the CMS experiment at the LHC using a data sample of $B_s \to J/ψ(μ^+μ^−)ϕ(K^+K^−)$ decays. The analysed dataset corresponds to an integrated luminosity of about $20fb^{−1}$ collected in pp collisions at a centre-of-mass energy $\sqrt{s}$=8TeV . 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 difference between the B s mass eigenstates is $ΔΓ_s$=0.096±0.014(stat.)±0.007(syst.)$ps^{−1}$ .