In this paper the branching ratios of the measured decay KL→π^+π^-e^+e^- and of the still unmeasured decay K^+→π^+π⁰e^+e^- are calculated to next-to-leading order in Chiral Perturbation Theory (CHPT). Recent experimental results are used to determine two possible values of the combination (N₁6ʳ - N₁7) of weak low-energy couplings (LEC) from the O (p⁴) chiral Lagrangian. Furthermore, the obtained values are compared to theoretical models of weak counter-term couplings to distinguish between the two possibilities. Using the favoured value of the combination (N₁6ʳ - N₁7) and taking into account additional assumptions suggested by these models, one can predict the branching ratio of the second decay as a function of the numerically unknown combination (N₁4ʳ+ 2N₁5ʳ) of weak low-energy couplings. Finally, making use of a particular model for the individual LECs, one predicts the decay width of the K^+ decay in question.
Pichl Hannes (Sat,) studied this question.