Charmonium decays to gamma pi0, gamma eta, and gamma eta'

TL;DR

This paper reports precise measurements of branching fractions for charmonium decays to gamma pi0, gamma eta, and gamma eta' using CLEO-c data, revealing unexpected differences in decay ratios among states.

Contribution

It provides new, more accurate measurements of decay branching fractions and ratios for J/psi, psi(2S), and psi(3770), highlighting unexpected results in decay ratios.

Findings

R_1 = (21.1 +- 0.9)% for J/psi

R_2 < 1.8% for psi(2S)

Improved precision in eta' decay modes

Abstract

Using data acquired with the CLEO-c detector at the CESR e+e- collider, we measure branching fractions for J/psi, psi(2S), and psi(3770) decays to gamma pi0, gamma eta, and gamma eta'. Defining R_n = B[ psi(nS)-->gamma eta ]/B[ psi(nS)-->gamma eta' ], we obtain R_1 = (21.1 +- 0.9)% and, unexpectedly, an order of magnitude smaller limit, R_2 < 1.8% at 90% C.L. We also use J/psi-->gamma eta' events to determine branching fractions of improved precision for the five most copious eta' decay modes.