Measurement of CP violation in B0→D+D− and B0s→D+sD−s decays

A time-dependent, favour-tagged measurement of CP violation is performed with B0 → D+D− and B0s → D+s D−s decays, using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 6 fb−1. In B0 → D+D− decays the CP-violation parameters are measured to be SD+D− = −0.552 ± 0.100 (stat) ± 0.010 (syst), CD+D− = 0.128 ± 0.103 (stat) ± 0.010 (syst). In B0s → D+s D−s decays the CP-violating parameter formulation in terms of ϕs and |λ| results in ϕs = −0.086 ± 0.106 (stat) ± 0.028 (syst) rad, |λD+s D−s| = 1.145 ± 0.126 (stat) ± 0.031 (syst). These results represent the most precise single measurement of the CP-violation parameters in their respective channels. For the frst time in a single measurement, CP symmetry is observed to be violated in B0 → D+D− decays with a significance exceeding six standard deviations.