Measurement of the decay rate and form factor parameter alpha(K*) in the decay K-L -> e(+)e(-)gamma

The decay rate of the neutral K meson K-L --> 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 Gamma(K-L --> e(+)e(-)gamma)/Gamma(K-L --> all) = (1.06 +/- 0.02(stat) +/- 0.02(sys) +/- 0.04(calc)) X 10(-5). The parameter alpha(K*) describing the relative strength of the two contributing amplitudes to this decay through intermediate pseudoscalar or vector mesons was measured to be alpha(K*) = -0.36 +/- 0.06(stat) +/- 0.02(sys). (C) 1999 Published by Elsevier Science B.V. All rights reserved.