A Measurement of the Branching Ratio of $K_L \to e^+e^-\gamma\gamma$

TL;DR

This paper reports a precise measurement of the branching ratio for the rare decay $K_L o e^+e^- ext{gamma} ext{gamma}$ using Fermilab data, including background estimation and form factor analysis.

Contribution

The study provides the first detailed measurement of the branching ratio for this decay mode, incorporating an effective form factor and background correction.

Findings

Branching ratio measured as (5.84 ± 0.15 (stat) ± 0.32 (sys))×10^{-7}.

Sample of 1543 events with 56 ± 8 background events.

Effective form factor determined from the data.

Abstract

We report on a study of the decay $K_L \to e^+e^-\gamma\gamma$ carried out as a part of the KTeV/E799 experiment at Fermilab. The 1997 data yielded a sample of 1543 events, including an expected background of $56 \pm 8$ events. An effective form factor was determined from the observed distribution of the $e^+e^-$ invariant mass. Using this form factor in the calculation of the detector acceptance, the branching ratio was measured to be ${\mathcal B}(K_L \to e^+ e^- \gamma \gamma, E^*_\gamma > 5 {MeV}) = (5.84 \pm 0.15 {\rm ~(stat)} \pm 0.32 {\rm ~(sys)})\times 10^{-7}$.