Search for the decays $η^{\prime} \to e^+e^-$ and $η\to e^+e^-$ at the VEPP-2000 $e^+e^-$ collider

Abstract

A search for the rare decay $η^{\prime} \to e^+e^-$ has been performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The inverse reaction $e^+e^- \to η^{\prime}$ and $η^{\prime}$ five decay chains have been used for this search. The upper limit $Γ_{η^{\prime} \to e^+e^-}<0.002$ eV at the 90\% confidence level has been set. A sensitivity of SND in a search for $η\to e^+e^-$ decay has been studied. For this perpose we have analyzed a data sample with an integrated luminosity of 108 nb$^{-1}$ collected in the center-of-mass energy range 520-580 MeV. There are no background events for the reaction $e^+e^- \to η$ with decay $η\to π^0π^0π^0$ have been found. In the absence of background, a sensitivity to $B(η\to e^+e^-)$ of 10$^{-6}$ can be reached during two weeks of VEPP-2000 operation.