Improved measurements of two-photon widths of the ${\chi }_{cJ}$ states and helicity analysis for ${\chi }_{c2}\to \gamma \gamma$

BESIII Collaboration, M. Ablikim, M. N. Achasov +435

Based on $448.1\times 10^6$ $\psi (3686)$ events collected with the BESIII detector, the decays $\psi (3686)\to \gamma {\chi }_{cJ},{\chi }_{cJ}\to \gamma \gamma (J=0,1,2)$ are studied. The decay branching fractio…