Observation of Y(2175) in $J\mathrm{/}\psi \to \eta \varphi f_0(980)$

The decays of $J/\psi\to \eta\phi f_0(980) (\eta\to \gamma\gamma, \phi \to K^+K^-, f_0(980)\to\pi^+\pi^-)$areanalyzedusingasampleof$5.8 \times 10^{7}$ $J\mathrm{/}\psi$ events collected with the BESII detector at the Beijing Electron-Positron Collider (BEPC). A structure at around $2.18$GeV/$c^2$ with about $5\sigma$ significance is observed in the $\varphi f_0(980)$ invariant mass spectrum. A fit with a Breit-Wigner function gives the peak mass and width of $m=2.186\pm 0.010(stat)\pm 0.006(syst)$GeV/$c^2$ and $\Gamma=0.065\pm 0.023 (stat)\pm 0.017 (syst) $GeV\mathrm{/}$c^2$, respectively, that are consistent with those of Y(2175), observed by the BABAR collaboration in the initial-state radiation (ISR) process $e^{+}{e}^{-}\to {\gamma }_{ISR}\varphi f_0(980)$. The production branching ratio is determined to be $Br(J/\psi\to\eta Y(2175))\cdot Br(Y(2175)\to\phi f_0(980))\cdot Br(f_0(980)\to\pi^+\pi^-)=(3.23\pm 0.75 (stat)\pm0.73 (syst))\times 10^{-4}$,assumingthattheY(2175)isa$1^{–}$ state.