Evidence of $\ddot{I}ƒ$ particle in $J/\ddot{I}ˆ\to \ddot{I}‰\ddot{I}€\ddot{I}€$

Abstract

Based on a sample of 7.8 million BESI $J/\ddot{I}ˆ$ events, the decay of $J/\ddot{I}ˆ\to \ddot{I}‰\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ is studied. A low mass enhancement in the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ invariant mass spectrum recoiling against $\ddot{I}‰$ particle is clearly seen which does not come from the phase space effect and the background. According to PWA analysis, this low mass enhancement is a broad $0^{++}$ resonance, the $\ddot{I}ƒ$ particle. If a Breit-Winger function of constant width is used to fit the $\ddot{I}ƒ$ signal, its mass and width are $384\pm 66$ MeV and $458\pm 100$ MeV respectively, which correspond to the pole position at (434 $\pm$ 78) - $i$ (202 $\pm$ 43) MeV.

7 pages, 7 figures