Observation of D+→K+η(') and Search for CP Violation in D+→π+η(') Decays

We report the first observation of D+ K+*(′) and a search for CP violation in D+ +(′) decays using a 791 fb−1 data sample collected with the Belle detector at the KEKB asymmetric- energy e+e− collider. The ratio of the branching fractions of doubly Cabibbo-suppressed relative to singly Cabibbo-suppressed D+ +(′) decays are B(D+ K+)/B(D+ +) = (3.06 ± 0.43 ± 0.14)% and B(D+ K+′)/B(D+ +′) = (3.77 ± 0.39 ± 0.10)% , where the first uncertainties are statistical and the second are systematic. We also report the most precise measurements of CP asymmetries to date: AD+→+ CP = (+1.74 ± 1.13 ± 0.20)% and AD+→+′ CP = (−0.12 ± 1.12 ± 0.20)%, respectively.