Physics and outlook for rare, all-neutral Eta decays

TJNAF, 12000 Jefferson Avenue, Newport News, VA 23606, USA

^a e-mail: mack@jlab.org

Published online: 9 June 2014

Abstract

The η meson provides a laboratory to study isospin violation and search for new flavor-conserving sources of C and CP violation with a sensitivity approaching 10⁻⁶ of the isospin-conserving strong amplitude. Some of the most interesting rare η decays are the neutral modes, yet the effective loss of photons from the relatively common decay η → 3π⁰ → 6γ (33%) has largely obscured rare decays producing 3-5γ's. Particularly important relevant branches include the highly suppressed η → π⁰2γ → 4γ, which provides a rare window on testing models of O(p⁶) contributions in ChPTh, and η → 3γ and η → 2π⁰γ → 5γ which provide direct constraints on C violation in flavor-conserving processes. The substitution of lead tungstate in the forward calorimeter of the GluEx setup in Jefferson Lab's new Hall D would allow dramatically improved measurements. The main niche of this facility, which we call the JLab Eta Factory (JEF), would be η decay neutral modes. However, this could likely be expanded to rare η′(958) decays for low energy QCD studies as well as η decays involving muons for new physics searches.