Study of the decay ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{+}$${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$

We present results of an experiment in which approximately 500 events of the decay ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{+}$ ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ were observed. We have measured the branching ratio for ${\mathit{K}}_{\mathrm{\pi }\mathit{e}\mathit{e}}^{+}$ to be (2.75±0.23±0.13)×${10}^{\mathrm{-}7}$ assuming a vector interaction with a form factor of λ=0.105±0.035±0.015. We have also found the branching ratio times decay probability for ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{+}$ ${\mathit{X}}^0$, ${\mathit{X}}^0$→${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ to be less than 1.5×${10}^{\mathrm{-}8}$ (99% C.L.) over an ${\mathit{X}}^0$ invariant mass range from 150 to 340 MeV/${\mathit{c}}^2$.