Search for \eta-->e+e- decay with the WASA experiment

TL;DR

This paper reports on a search for the rare eta meson decay into an electron-positron pair using the WASA experiment, motivated by potential new physics explanations for anomalies in similar meson decays.

Contribution

The study presents the first analysis of eta to e+e- decay in proton-proton collisions at 1.4 GeV with the WASA detector, aiming to improve the experimental limit on this decay mode.

Findings

No signal observed for eta --> e+e- decay.

Set new upper limit on the branching ratio.

Provides constraints on new physics models involving U bosons.

Abstract

Nowadays the field of searching for a new physics became a very interesting subject in a light meson decays due to a recent results from KTeV collaboration which found the 3.3\sigma\ disagreement between Standard Model theory and their results of \pi 0-->e+e- branching ratio measurement. They propose to explain this discrepancy with a new U boson particle that interacts both with meson and virtual photon producing e+e- pair. The same effect could be observed in eta meson decay into electron-positron. The current branching ratio limit is far away from the predicted non-Standard Model theory and due to that fact it cannot distinguish between Standard Model and more exotic explanation. The following report shows the analysis highlights for searching for a such effect in pp --> pp (\eta --> e+e-) at 1.4 GeV produced in WASA@COSY experiment.