Observation of Y(2175) in $J/\ddot{I}ˆ\to \hat{I}\cdot \ddot{I}•f_0(980)$

Abstract

The decays of $J/\ddot{I}ˆ\to \hat{I}\cdot \ddot{I}•f_0(980)(\hat{I}\cdot \to {\hat{I}}^3{\hat{I}}^3,\ddot{I}•\to K^{+}{K}^{-},f_0(980)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-})$ are analyzed using a sample of $5.8\times 10^7$ $J/\ddot{I}ˆ$ events collected with the BESII detector at the Beijing Electron-Positron Collider (BEPC). A structure at around $2.18$GeV/$c^2$ with about $5\ddot{I}ƒ$ significance is observed in the $\ddot{I}•f_0(980)$ 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 $\hat{I}“=0.065\pm 0.023(stat)\pm 0.017(syst)$GeV/$c^2$, respectively, that are consistent with those of Y(2175), observed by the BABAR collaboration in the initial-state radiation (ISR) process $e^{+}{e}^{-}\to {\hat{I}}_{ISR}^3\ddot{I}•f_0(980)$. The production branching ratio is determined to be $Br(J/\ddot{I}ˆ\to \hat{I}\cdot Y(2175))\cdot Br(Y(2175)\to \ddot{I}•f_0(980))\cdot Br(f_0(980)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-})=(3.23\pm 0.75(stat)\pm 0.73(syst))\times 10^{-4}$, assuming that the Y(2175) is a $1^{--}$ state.

5 pages, 4 figures, accepted by Phys. Rev. Lett