Two-photon widths of the χc0,2 states and helicity analysis for χc2 → γγ

Based on a data sample of 106 X 10(6) psi' events collected with the BESIII detector, the decays psi' -> gamma chi(c0,2), chi(c0,2) -> gamma gamma are studied to determine the two-photon widths of the chi(c0,2) states. The two-photon decay branching fractions are determined to be B(chi(c0) -> gamma gamma) = (2.24 +/- 0.19 +/- 0.12 +/- 0.08) X 10(-4) and B(chi(c2) -> gamma gamma) = (3.21 +/- 0.18 +/- 0.17 +/- 0.13) X 10(-4) From these, the two-photon widths are determined to be Gamma(gamma gamma)(chi(c0)) = (2.33 +/- 0.20 +/- 0.13 +/- 0.17) keV, Gamma(gamma gamma)(chi(c2)) = (0.63 +/- 0.04 +/- 0.04 +/- 0.04) keV, and R = Gamma(gamma gamma)(chi(c2))/Gamma(gamma gamma)(chi(c0)) = 0.271 +/- 0.029 +/- 0.013 +/- 0.027, where the uncertainties are statistical, systematic, and those from the PDG B(psi' -> gamma chi(c0,2)) and Gamma(chi(c0,2)) errors, respectively. The ratio of the two-photon widths for helicity lambda = 0 and helicity lambda = 2 components in the decay chi -> gamma gamma is measured for the first time to be f(0/2) = Gamma(lambda=0)(gamma gamma)(chi(c2))/Gamma(lambda=2)(gamma gamma)(chi(c2)) = 0.00 +/- 0.02 +/- 0.02.