Observation of the double Dalitz decay $\eta'\to e^+e^-e^+e^-$

TL;DR

This paper reports the first observation of the double Dalitz decay of the eta prime meson, measuring its branching fraction with high statistical significance using a large data sample from BESIII.

Contribution

First observation of the eta prime double Dalitz decay via J/psi radiative decay, with a measured branching fraction and significance.

Findings

Branching fraction of (4.5 ± 1.0(stat.) ± 0.5(sys.)) × 10^{-6}

Significance of 5.7 sigma for the decay observation

Observation made using over 10 billion J/psi events

Abstract

Based on $(10087 \pm 44)\times10^6$ $J/\psi$ events collected with the BESIII detector at BEPCII, the double Dalitz decay $\eta'\to e^+e^-e^+e^-$ is observed for the first time via the $J/\psi\to\gamma\eta'$ decay process. The significance is found to be 5.7$\sigma$ with systematic uncertainties taken into consideration. Its branching fraction is determined to be $\mathcal{B}(\eta'\to e^+ e^- e^+ e^-) =(4.5\pm1.0(\mathrm{stat.})\pm0.5(\mathrm{sys.})) \times 10^{-6}$.