On a search for the $\eta \rightarrow e^+ e^-$ decay at the VEPP-2000 $e^+e^-$ collider

TL;DR

This paper evaluates the VEPP-2000 collider's potential to detect the rare decay $ ext{eta} ightarrow e^+ e^-$ by analyzing existing data and proposing an inverse reaction approach, achieving sensitivity surpassing current limits.

Contribution

The study demonstrates that VEPP-2000 can reach a sensitivity of $10^{-6}$ for $ ext{eta} ightarrow e^+ e^-$ decay, improving current upper limits by a factor of 2.3.

Findings

No background events observed in the analyzed data sample.

A sensitivity of $10^{-6}$ for the decay can be achieved in two weeks.

The approach surpasses existing upper limits on the decay's branching ratio.

Abstract

A sensitivity of the VEPP-2000 $e^+e^-$ collider in a search for the rare decay $\eta \rightarrow e^+ e^-$ has been studied. The inverse reaction $e^+ e^- \rightarrow \eta$ is proposed for this search. We have analyzed a data sample with an integrated luminosity of 108 nb$^{-1}$ collected with the SND detector in the center-of-mass energy range 520-580 MeV and found no background events for the reaction $e^+ e^- \rightarrow \eta$ in the decay mode $\eta\to\pi^0\pi^0\pi^0$. In the absence of background, a sensitivity to ${\cal B}(\eta \rightarrow e^+ e^-)$ of $10^{-6}$ can be reached during two weeks of VEPP-2000 operation. Such a sensitivity is better than the current upper limit on ${\cal B}(\eta \rightarrow e^+ e^-)$ by a factor of 2.3.