Direct CP violation in KL → π+π−γ

Abstract

CP violation due to interference between K L and K S decays into π + π − γ is analyzed in the Standard Model in conjunction with the large N c approach. The CP-violating parameter ϵ′ +− γ , which is the difference between η +− γ and η +−, receives dominant contributions from K 0− K 0 mixing and the gluon penguin diagram; its magnitude is calculated to be of order 10 −2ϵ. Genuine direct CP violation in K L → π + π − γ decay originating from the electromagnetic penguin diagram is of order (10 −3−10 −4)ϵ, depending on the region of the Dalitz plot.