Limit on the branching ratio of ${\mathit{K}}_{\mathit{L}}$→${\mathrm{\pi }}^0$${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$

We report the results of a search for the decay ${\mathit{K}}_{\mathit{L}}$→${\mathrm{\pi }}^0$ ${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$ conducted by E799 at Fermilab. This decay mode is expected to have significant CP-violating contributions and a direct measurement could either confirm the standard model mechanisms for CP-violation or point to physics beyond the standard model. No such events were seen. The 90% confidence level upper limit is determined to be B(${\mathit{K}}_{\mathit{L}}$→${\mathrm{\pi }}^0$ ${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$)<5.1×${10}^{\mathrm{-}9}$.