Measurement of time-dependent CP asymmetries in B^0 Kₒ^0 ^+ ^- decays at Belle and Belle II

A bstract We present a measurement of the time-dependent CP asymmetry in B^0 Kₒ^0 ^+ ^- decays using a data set of 365 fb − 1 recorded by the Belle II experiment and the final data set of 711 fb − 1 recorded by the Belle experiment at the Υ (4S) resonance. The direct and mixing-induced time-dependent CP violation parameters C and S are determined along with two additional quantities, S + and S −, defined in the two halves of the m^2 (Kₒ^0 ^+) -m^2 (Kₒ^0 ^-) plane. The measured values are C = − 0. 17 ± 0. 09 ± 0. 04, S = − 0. 29 ± 0. 11 ± 0. 05, S + = −0. 57 ± 0. 23 ± 0. 10 and S − = 0. 31 ± 0. 24 ± 0. 05, where the first uncertainty is statistical and the second systematic.