Interference of conversion and bremsstrahlung amplitudes in the decay KL→μ+μ−γ

In the region of large μ+μ− invariant mass, the decay spectrum of KL→μ+μ−γ deviates from the Dalitz pair spectrum, as a result of interference between conversion (KL→γ∗γ→μ+μ−γ) and bremsstrahlung amplitudes. The latter is proportional to the KL→μ+μ− matrix element, whose 2γ-absorptive part appears to dominate the observed KL→μ+μ− decay rate. We examine the extent to which a scrutiny of the KL→μ+μ−γ spectrum in the end-point region could provide evidence on the real part of the KL→μ+μ− amplitude. As a by-product, we obtain the absorptive part of the KL→γ∗γ form factor, using data on the KL→π+π−γ spectrum.