Measurements of the Decay $K_L\to e^{+}{e}^{-}\gamma$

Abstract

The E799-II (KTeV) experiment at Fermilab has collected 83262 $K_L\to e^{+}{e}^{-}\gamma$ events above a background of 79 events. We measure a decay width, normalized to the $K_L\to {\pi }^0{\pi }^0{\pi }_D^0$ (π^0 \to γγ, π^0 to γγ, π^0_D \to e^+e^-γ) decay width, of $\Gamma ($K_L \to e^+e^-γ$)/\Gamma (K_L\to {\pi }^0{\pi }^0{\pi }_D^0)=(1.3302\pm 0.0046_{stat}\pm 0.0102_{syst})\times 10^{-3}$. We also measure parameters of two $K_L{\gamma }^{\ast }\gamma$ form factor models. In the Bergstrom, Masso, and Singer (BMS) parametrization, we find $\caks = -0.517 \pm 0.030_{stat} \pm 0.022_{syst}$. We separately fit for the first parameter of the D'Ambrosio, Isidori, and Portoles (DIP) model and find $\adip = -1.729 \pm 0.043_{stat} \pm 0.028_{syst}$.

5 pages, 3 figures, submitted to PRL