Tests of the fundamental symmetries in eta meson decays

TL;DR

This paper reviews experimental tests of fundamental symmetries in eta meson decays, including searches for rare and forbidden decay modes and asymmetries, conducted at several European accelerator facilities.

Contribution

It provides a comprehensive overview of current experimental efforts to test C, P, and CP symmetries in eta meson decays across multiple research facilities.

Findings

Limits set on rare decay branching ratios

No significant CP violation observed in eta decays

Constraints on symmetry-violating processes in meson decays

Abstract

Patterns of chiral symmetry violation and tests of the conservation of the fundamental C, P and CP symmetries are key physics issues in studies of the pi0, eta and eta' meson decays. These tests include searches for rare or forbidden decays and searches for asymmetries among the decay products in the not-so-rare decays. Some examples for the rare decays are eta-->2pi, eta-->4pi0 (CP tests), decays into an odd number of photons (e.g., eta-->3g) and the decay eta-->pi0e+e- (C tests). The experimental studies of the pi0, eta and eta' meson decays are carried out at four European accelerator research facilities: KLOE/KLOE-2 at DAFNE (Frascati), Crystal Ball at MAMI (Mainz), WASA at COSY (J\"ulich), Crystal Barrel at ELSA (Bonn).