The decays K → πℓ+ℓ- beyond leading order in the chiral expansion

Abstract

We present a model-independent analysis of K+ → π+ℓ+ℓ- and KS → π0ℓ+ℓ- decays, including K → 3π unitarity corrections and a general decomposition of the dispersive amplitude. From the existing data on K+ → π+ℓ+ℓ- we predict the ratio R = B(K+ → π+μ+μ-)/B(K+ → π+e+e-) to be larger than 0.23, in slight disagreement with the recent measurement R = 0.167 ± 0.036. Consequences for the K± → π±e+e- charge asymmetries and for the KL → π0e+e- mode are also discussed.