Observation of a pseudoscalar state in J/ psi --> gamma phi phi near phi phi threshold.

Abstract

We present a study of the radiative decay J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\varphi}\ensuremath{\varphi} in the \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ and \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}_{\mathit{S}}^{0}$${\mathit{K}}_{\mathit{L}}^{0}$ final states. A pseudoscalar state is observed in the \ensuremath{\varphi}\ensuremath{\varphi} invariant-mass spectrum at 2.22 GeV/${\mathit{c}}^{2}$ with a width of 150 MeV/${\mathit{c}}^{2}$. The product branching ratios are B(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}X)B(X\ensuremath{\rightarrow}\ensuremath{\varphi}\ensuremath{\varphi})=(3.3\ifmmode\pm\else\textpm\fi{}0.8\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ for the \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ mode and B(J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\gamma}X)B(X\ensuremath{\rightarrow}\ensuremath{\varphi}\ensuremath{\varphi})=(2.7\ifmmode\pm\else\textpm\fi{}0.6 \ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ for the \ensuremath{\gamma}${\mathit{K}}^{+}$${\mathit{K}}^{\mathrm{\ensuremath{-}}}$${\mathit{K}}_{\mathit{S}}^{0}$${\mathit{K}}_{\mathit{L}}^{0}$ mode. No evidence for ${2}^{++}$ states below 2.4 GeV/${\mathit{c}}^{2}$ is found in this radiative J/\ensuremath{\psi} decay mode.