Study of $\psi(2S)$ decays into $\gamma K^+K^-$ and $\gamma \pi^+\pi^-$

TL;DR

This paper analyzes radiative decays of $ ext{ψ(2S)}$ into $ ext{γ}K^+K^-$ and $ ext{γ} ext{π}^+ ext{π}^-$, measuring branching fractions and angular distributions to study intermediate resonances and decay dynamics.

Contribution

It provides new measurements of branching fractions and angular distributions for $ ext{ψ(2S)}$ radiative decays into specific meson pairs, identifying contributions from various scalar and tensor mesons.

Findings

Measured product branching fractions for $ ext{ψ(2S)}$ decays into specific resonances.

Performed angular analysis to determine helicity ratios of $f_2(1270)$.

Identified contributions of multiple scalar and tensor mesons in decay channels.

Abstract

Radiative charmonium decays from the BESII sample of 14$\times10^{6}$ $\psi(2S)$-events into two different final states, $\gamma K^+K^-$ and $\gamma\pi^+\pi^-$, are analyzed. Product branching fractions for $\psi(2S)\to\gamma X\to \gamma\pi^+\pi^-$, $\gamma K^+K^-$ are given, where $X=f_2(1270)$, $f_0(1500)$, and $f_0(1710)$ in $\pi^+\pi^-$ and $f_2(1270)$, $f_2'(1525)$, and $f_0(1700)$ in $K^+K^-$. An angular analysis gives the ratios of the helicity projections for the $f_2(1270)$ in $\psi(2S)\to\gamma f_2(1270)\to\gamma\pi^+\pi^-$.