Improved measurements of two-photon widths of the χcJ states and helicity analysis for χc2→γγ

Le résumé fourni par la source

Based on $448.1\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\ensuremath{\psi}(3686)$ events collected with the BESIII detector, the decays $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\chi}}_{cJ},\phantom{\rule{0ex}{0ex}}{\ensuremath{\chi}}_{cJ}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}(J=0,1,2)$ are studied. The decay branching fractions of ${\ensuremath{\chi}}_{c0,2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ are measured to be $\mathcal{B}({\ensuremath{\chi}}_{c0}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})=(1.93\ifmmode\pm\else\textpm\fi{}0.08\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $\mathcal{B}({\ensuremath{\chi}}_{c2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})=(3.10\ifmmode\pm\else\textpm\fi{}0.09\ifmmode\pm\else\textpm\fi{}0.07\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, which correspond to two-photon decay widths of ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}({\ensuremath{\chi}}_{c0})=2.03\ifmmode\pm\else\textpm\fi{}0.08\ifmmode\pm\else\textpm\fi{}0.06\ifmmode\pm\else\textpm\fi{}0.13\text{ }\text{ }\mathrm{keV}$ and ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}({\ensuremath{\chi}}_{c2})=0.60\ifmmode\pm\else\textpm\fi{}0.02\ifmmode\pm\else\textpm\fi{}0.01\ifmmode\pm\else\textpm\fi{}0.04\text{ }\text{ }\mathrm{keV}$ with a ratio of $\mathcal{R}={\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}({\ensuremath{\chi}}_{c2})/{\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}({\ensuremath{\chi}}_{c0})=0.295\ifmmode\pm\else\textpm\fi{}0.014\ifmmode\pm\else\textpm\fi{}0.007\ifmmode\pm\else\textpm\fi{}0.027$, where the uncertainties are statistical, systematic and associated with the uncertainties of $\mathcal{B}(\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\chi}}_{c0,2})$ and the total widths $\mathrm{\ensuremath{\Gamma}}({\ensuremath{\chi}}_{c0,2})$, respectively. For the forbidden decay of ${\ensuremath{\chi}}_{c1}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$, no signal is observed, and an upper limit on the two-photon width is obtained to be ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}({\ensuremath{\chi}}_{c1})<5.3\text{ }\text{ }\mathrm{eV}$ at the 90% confidence level. The ratio of the two-photon widths between helicity-zero and helicity-two components in the decay ${\ensuremath{\chi}}_{c2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ is also measured to be ${f}_{0/2}={\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}^{\ensuremath{\lambda}=0}({\ensuremath{\chi}}_{c2})/{\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}^{\ensuremath{\lambda}=2}({\ensuremath{\chi}}_{c2})=(0.0\ifmmode\pm\else\textpm\fi{}0.6\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$, where the uncertainties are statistical and systematic, respectively.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.