Measurement of the chi_{c2} Polarization in psi(2S) to gamma chi_{c2}

TL;DR

This paper measures the polarization of chi_{c2} in psi(2S) decays, confirming it aligns with a pure E1 transition and finding no significant M2 or E3 contributions, using a large BESII data sample.

Contribution

First measurement of chi_{c2} polarization in psi(2S) decays confirming E1 dominance with detailed angular analysis.

Findings

Polarization consistent with pure E1 transition

No significant M2 or E3 contributions detected

Helicity amplitude ratios measured with high precision

Abstract

The polarization of the chi_{c2} produced in psi(2S) decays into gamma chi_{c2} is measured using a sample of 14*10^6 psi(2S) events collected by BESII at the BEPC. A fit to the chi_{c2} production and decay angular distributions in psi(2S) to gamma chi_{c2}, chi_{c2} to pi pi and KK yields values x=A_1/A_0=2.08+/-0.44 and y=A_2/A_0=3.03 +/-0.66, with a correlation rho=0.92 between them, where A_{0,1,2} are the chi_{c2} helicity amplitudes. The measurement agrees with a pure E1 transition, and M2 and E3 contributions do not differ significantly from zero.