First evidence of CP violation in beauty baryon to charmonium decays.

A study of the difference in the CP asymmetries between Λb0→J/ψpπ- and Λb0→J/ψpK- decays, ΔACP, is performed using proton-proton collision data collected by the LHCb experiment in the years 2015-2018, corresponding to an integrated luminosity of 6fb-1. This quantity is measured to be ΔACP=(4.03±1.18±0.23)%, where the first uncertainty is statistical and the second is systematic. When combined with the previous LHCb result, a value of ΔACP=(4.31±1.06±0.28)% is obtained, corresponding to a significance of 3.9σ against the CP symmetry hypothesis. Studies of triple-product asymmetries, which provide an additional probe of CP violation, show no significant deviation from CP symmetry.