Long distance contribution to KL → ℓ+ℓ− Original Research Article

We revisit the calculation of the long distance contribution to KL → μ+ μ−. We discuss this process within the framework of chiral perturbation theory, and also using simple models for the KLγ∗γ∗ vertex. We argue that it is unlikely that this mode can be used to extract information on short distance parameters. The process KL → e+ e− is also long-distance dominated and we find that B(KL → e+ e−9 x 10−12.