A New Upper Limit on the Decay $\eta\to e^{+}e^{-}$

TL;DR

This paper reports a search for the rare eta meson decay into an electron-positron pair, setting a new upper limit on its branching fraction, which is significantly higher than theoretical predictions.

Contribution

The study provides the first experimental upper limit on the eta to electron-positron decay branching fraction using data from the CLEO II detector.

Findings

Upper limit on $B( o e^{+}e^{-}) < 7.7 imes 10^{-5}$ at 90% confidence

Experimental limit is much higher than the theoretical prediction of about $10^{-9}$

Demonstrates the sensitivity of current detectors to rare meson decays.

Abstract

We have searched for the rare decay of the eta meson $\eta \to e^{+}e^{-}$ using the CLEO II detector. The $\eta$'s were produced in $e^{+}e^{-}$ collisions with 10 GeV center-of-mass energy at the Cornell Electron Storage Ring (CESR). We find with 90% confidence the upper limit on the branching fraction $B(\eta \to e^{+}e^{-}) < 7.7\times 10^{-5}$. The application of conventional elementary particle theory to this decay predicts a branching fraction of about $10^{-9}$.