Search for the process $\mathbf{e^+e^- \to\eta}$

TL;DR

This study searches for the rare decay $ ext{eta} ightarrow e^+ e^-$ by analyzing $e^+ e^- o ext{eta}$ events at VEPP-2000, setting an upper limit on the decay's branching ratio.

Contribution

It provides the first upper limit on the decay $ ext{eta} ightarrow e^+ e^-$ using inverse process data at VEPP-2000.

Findings

Upper limit on $ ext{eta} ightarrow e^+ e^-$ branching ratio: $7 imes 10^{-7}$

Data collected at center-of-mass energy near $ ext{eta}$ mass

Analysis constrains rare decay processes of eta meson.

Abstract

A search for the rare decay $\eta \rightarrow e^+e^-$ is performed using the inverse process $e^+e^- \rightarrow \eta$ in the decay mode $\eta\to\pi^0\pi^0\pi^0 $. We analyze data with an integrated luminosity of 654 nb$^{-1} $ accumulated at the VEPP-2000 $e^+e^-$ collider with the SND detector at the center-of-mass energy $E=m_\eta c ^2\approx 548 $ MeV, and set the upper limit $ {\cal B} (\eta \rightarrow e^+ e^-) < 7 \times 10^{-7} $ at the 90\% confidence level.