A Measurement of the Branching Ratio and Form Factor of K_L->mu mu gamma

TL;DR

This paper reports the first measurement of the branching ratio and form factor of the decay K_L to mu+ mu- gamma, providing new insights into kaon decay dynamics and form factors.

Contribution

It presents the first measurement of the K gamma gamma* form factor in the muonic Dalitz decay mode of the K_L.

Findings

Branching ratio B(K_L→μ+μ−γ) = (3.23 ± 0.23 (stat) ± 0.19 (sys)) × 10^{-7}

Observed 207 candidate events with estimated background of 10.5 ± 4.0 events

First measurement of the K gamma gamma* form factor in this decay mode.

Abstract

We report on a measurement of the decay $K_L\rightarrow\mu^+\mu^-\gamma$ from Fermilab experiment E799. We observe $207$ candidate signal events with an estimated background of $10.5 \pm 4.0$ events and establish $B(K_L\rightarrow\mu^+\mu^-\gamma) = (3.23\pm 0.23(stat) \pm 0.19(sys))\times 10^{-7}$. This provides the first measurement of the $K\gamma\gamma^*$ form factor in the muonic Dalitz decay mode of the $K_L$.