Measurement of CP Violation in B0 →ψ (→ℓ+ℓ-) KS0 (→π+π-) Decays

A measurement of time-dependent CP violation in the decays of B0 and B¯0 mesons to the final states J/ψ(→μ+μ-)KS0, ψ(2S)(→μ+μ-)KS0 and J/ψ(→e+e-)KS0 with KS0→π+π- is presented. The data correspond to an integrated luminosity of 6 fb-1 collected at a center-of-mass energy of s=13 TeV with the LHCb detector. The CP-violation parameters are measured to be SψKS0=0.717±0.013(stat)±0.008(syst) and CψKS0=0.008±0.012(stat)±0.003(syst). This measurement of SψKS0 represents the most precise single measurement of the CKM angle β to date and is more precise than the current world average. In addition, measurements of the CP-violation parameters of the individual channels are reported and a combination with the LHCb Run 1 measurements is performed.