Measurement of CP violation in B0→ψ(→ℓ+ℓ−)KS0(→π+π−)B0→ψ(→ℓ+ℓ−)KS0​(→π+π−) decays

A measurement of time-dependent CP violation in the decays of B0 and B0 mesons to the final states J/ψ(→ μ+μ−)K0 S, ψ(2S) (→ μ+μ−)K0 S and J/ψ(→ e+e−)K0 S with K0 S → π+π− is presented. The data correspond to an integrated luminosity of 6 fb−1 collected at a centre-of-mass energy of √s = 13 TeV with the LHCb detector. The CP -violation parameters are measured to be SψK0 S = 0.717 ± 0.013 (stat) ± 0.008 (syst), CψK0 S = 0.008 ± 0.012 (stat) ± 0.003 (syst). This measurement of SψK0 S 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.