Observation ofY(2175)inJ/ψ→ηϕf0(980)

The decays of $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\phi}{f}_{0}(980)[\ensuremath{\eta}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma},\ensuremath{\phi}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}},{f}_{0}(980)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}]$ are analyzed using a sample of $5.8\ifmmode\times\else\texttimes\fi{}{10}^{7}$ $J/\ensuremath{\psi}$ events collected with the BESII detector at the Beijing Electron-Positron Collider. A structure at around $2.18\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ with about $5\ensuremath{\sigma}$ significance is observed in the $\ensuremath{\phi}{f}_{0}(980)$ invariant mass spectrum. A fit with a Breit-Wigner function gives the peak mass and width of $m=2.186\ifmmode\pm\else\textpm\fi{}0.010(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.006(\mathrm{syst})\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ and $\ensuremath{\Gamma}=0.065\ifmmode\pm\else\textpm\fi{}0.023(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.017(\mathrm{syst})\text{ }\text{ }\mathrm{GeV}/{c}^{2}$, respectively, which are consistent with those of $Y(2175)$, observed by the BABAR Collaboration in the initial-state radiation process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\gamma}}_{\mathrm{ISR}}\ensuremath{\phi}{f}_{0}(980)$. The production branching ratio is determined to be $\mathrm{Br}\mathbf{(}J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\eta}Y(2175)\mathbf{)}\mathrm{Br}\mathbf{(}Y(2175)\ensuremath{\rightarrow}\ensuremath{\phi}{f}_{0}(980)\mathbf{)}\mathrm{Br}\mathbf{(}{f}_{0}(980)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\mathbf{)}=[3.23\ifmmode\pm\else\textpm\fi{}0.75(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.73(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0ex}{0ex}}{10}^{\ensuremath{-}4}$, assuming that the $Y(2175)$ is a ${1}^{--}$ state.