Observation of $Y(2175)$ in $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\phi}{f}_{0}(980)$

Observation of $Y (2175)$ in $J / ψ \to η ϕ f_{0} (980)$

M. Ablikim et al. (BES Collaboration)

Phys. Rev. Lett. 100, 102003 – Published 12 March 2008

Abstract

The decays of $J / ψ \to η ϕ f_{0} (980) [η \to γ γ, ϕ \to K^{+} K^{-}, f_{0} (980) \to π^{+} π^{-}]$ are analyzed using a sample of $5.8 \times 10^{7}$ $J / ψ$ events collected with the BESII detector at the Beijing Electron-Positron Collider. A structure at around $2.18 GeV / c^{2}$ with about $5 σ$ significance is observed in the $ϕ f_{0} (980)$ 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 $Γ = 0.065 \pm 0.023 (stat) \pm 0.017 (syst) GeV / c^{2}$ , respectively, which are consistent with those of $Y (2175)$ , observed by the BABAR Collaboration in the initial-state radiation process $e^{+} e^{-} \to γ_{ISR} ϕ f_{0} (980)$ . The production branching ratio is determined to be $Br (J / ψ \to η Y (2175)) Br (Y (2175) \to ϕ f_{0} (980)) Br (f_{0} (980) \to π^{+} π^{-}) = [3.23 \pm 0.75 (stat) \pm 0.73 (syst)] \times 10^{- 4}$ , assuming that the $Y (2175)$ is a $1^{--}$ state.