Measurement of <i>CP</i> Violation in <i>B</i><SUP>0</SUP> → ψ(→ <i>l</i><SUP>+</SUP> <i>l</i><SUP>-</SUP>)<i>K_S</i><SUP>0</SUP>(→ π<SUP>+</SUP> π<SUP>-</SUP>) Decays

A measurement of time-dependent CP violation in the decays of B-0 and (B) over bar (0) mesons to the final states J/psi(-> mu(+) mu(-))K-S(0), psi(2S)(-> mu(+) mu(-))K-S(0) and J/psi(-> e(+)e(-))K-S(0) with K-S(0) -> pi(+)pi(-) is presented. The data correspond to an integrated luminosity of 6 fb(-1) collected at a center-of-mass energy of root s = 13 TeV with the LHCb detector. The CP-violation parameters are measured to be S-psi KS0 = 0.717 +/- 0.013(stat) +/- 0.008(syst) and C-psi KS0 = 0.008 +/- 0.012(stat) +/- 0.003(syst). This measurement of S-psi KS0 represents the most precise single measurement of the CKM angle beta 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.