Formula omitted] at O( p4) in the chiral expansion

Abstract

After updating the determination of the combination of Kobayashi-Maskawa elements Im V tdV ts ∗ according to our new estimate of the parameter B ̂ K , we study the CP-violating ratio ε′ ε by means of hadronic matrix elements computed to O( p 4) in the chiral expansion. It is the first time that this order in chiral perturbation theory is included. We also discuss the relevance of some O( p 2) terms that are generally neglected in the calculation of the electroweak penguin matrix elements. The most important effect of this improved analysis is the substantial reduction (20%) of the leading electroweak penguin matrix element and accordingly a reduced cancelation between the electroweak and gluon penguin contributions. The ratio ε′ ε is thus larger than previously estimated and its predicted value enjoys a smaller uncertainty. We find ε′/ ε = 1.7 −1.0 +1.4 × 10 −3. Values positive and of the order of 10 −3 are therefore preferred.