Measurement of the decay rate and form factor parameter $\alpha_{K^{*}}$ in the decay $K_{L} \rightarrow e^{+}e^{-}\gamma$

The decay rate of the neutral K meson $\mathrm{K_{L} \rightarrow e^{+}e^{-}\gamma}$ has been measured with the NA48 detector at the CERN SPS. A total of 6864 events has been observed with an estimated background of 10 events. The branching ratio is $\mathrm{\Gamma(K_{L} \rightarrow e^{+}e^{-}\gamma)/\Gamma(K_{L} rightarrow all) = (1.06 \pm 0.02_{stat.} \pm 0.02_{sys.} \pm 0.04_{calc.})\times 10^{-5}}$. The parameter describing the relative strength of the two contributing amplitudes to this decay through $\mathrm{\alpha_{K^{*}}}$ intermediate seudoscalar or vector mesons, was measured to be $\mathrm{\alpha_{K^{*}} = -0.36 \pm 0.06_{stat.} \pm 0.02_{sys.}}$