Two-Photon Widths of the chi_cJ States of Charmonium

TL;DR

This study measures the two-photon decay widths of chi_cJ charmonium states using psi(2S) decays, providing new experimental data crucial for understanding charmonium structure and testing quantum chromodynamics predictions.

Contribution

First measurement of two-photon widths of chi_cJ states via psi(2S) decays, with derived values and upper limit for chi_c1, advancing charmonium decay understanding.

Findings

Measured two-photon widths: chi_c0 = 2.53 keV, chi_c2 = 0.60 keV.

Determined ratio R = 0.237 for chi_c2 to chi_c0 widths.

Established upper limit for chi_c1 two-photon width at 0.03 keV.

Abstract

Using a data sample of 24.5 million psi(2S) the reactions psi(2S)->gamma chi_cJ, chi_cJ->gamma gamma have been studied for the first time to determine the two-photon widths of the chi_cJ states of charmonium in their decay into two photons. The measured quantities are B(psi(2S)->gamma chi_c0)xB(chi_c0->gamma gamma)=(2.22+-0.32+-0.10)x10^-5, and B(psi(2S)->gamma chi_c2)xB(chi_c2->gamma gamma)=(2.70+-0.28+-0.15)x10^-5. Using values for B(psi(2S)->gamma chi_c0,c2) and \Gamma(chi_c0,c2) from the literature the two-photon widths are derived to be \Gamma_{gamma gamma}(chi_c0)=(2.53+-0.37+-0.26) keV, \Gamma_{gamma gamma}(chi_c2)=(0.60+-0.06+-0.06) keV, and R=\Gamma_{gamma gamma}(chi_c2)/\Gamma_{gamma gamma}(chi_c0)= 0.237+-0.043+-0.034. The importance of the measurement of R is emphasized. For the forbidden transition, chi_c1->gamma gamma, an upper limit of \Gamma_{gamma gamma}(chi_c1)<0.03 keV is established.