Measurement of the decay rate and the parameter $\alpha_{K}^{\ast}$ of the decay K$_{L} \rightarrow \mu \mu \gamma$

The rate of the decay of the neutral K meson into K-L(0) --> mu mu gamma has been measured with the NA48 detector at the CERN SPS, Pi total of 59 events has been observed with an estimated background of 14 events. The overall Kaon flux was determined to he 1.2 x 10(9), This observation corresponds to a branching ratio of (3.4 +/- 0.6(stat) +/- 0.4(sys)) x 10(-7) Using this branching ratio the parameter alpha(K*) describing the relative strength of the two contributing amplitudes to this decay, through intermediate pseudoscalar or vectorlike mesons, was measured to be alpha(K*) = -0.04(-0.21)(+0.24).