Radiative Decay of the \psi(2S) into Two Pseudoscalar Mesons

TL;DR

This paper reports measurements of radiative decay branching ratios of the (2S) resonance into various meson pairs, providing insights into charmonium decay mechanisms and testing the 15% rule in quantum chromodynamics.

Contribution

First measurement of (2S) radiative decay rates into specific meson states, comparing them to J/ decays to test theoretical predictions.

Findings

Measured (2S) radiative decay branching ratios.

Found decay rates consistent with the 15% rule.

Provided data for charmonium decay models.

Abstract

Radiative decays of the radially excited charmonium resonance, \psi(2S), into \pi\pi, K Kbar and \eta\eta final states have been measured in a sample of 3.96 * 10^6 \psi(2S) events collected by the BES collaboration. The branching ratios B(\psi(2S) -> \gamma f_{2}(1270)) = (2.27 +- 0.26 +- 0.39) * 10^{-4} and B(\psi(2S) -> \gamma f_0(1710)) * B(f_0(1710) -> K^+ K^-) = (5.59 +- 1.12 +- 0.93) * 10^{-5} are obtained. When compared to the corresponding radiative J/\psi decays, the observed \psi(2S) radiative decay rates into \gamma f_2(1270) and \gamma f_0(1710) are consistent with the 15% rule.