Observation of the isospin-violating decay $J/\ddot{I}ˆ\to \ddot{I}•\ddot{I}{€}^0{f}_0(980)$

Abstract

Using a sample of 1.31 billion $J/\ddot{I}ˆ$ events collected with the BESIII detector at the BEPCII collider, the decays $J/\ddot{I}ˆ\to \ddot{I}•\ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^0$ and $J/\ddot{I}ˆ\to \ddot{I}•\ddot{I}{€}^0\ddot{I}{€}^0\ddot{I}{€}^0$ are investigated. The isospin violating decay $J/\ddot{I}ˆ\to \ddot{I}•\ddot{I}{€}^0{f}_0(980)$ with $f_0(980)\to \ddot{I}€\ddot{I}€$, is observed for the first time. The width of the $f_0(980)$ obtained from the dipion mass spectrum is found to be much smaller than the world average value. In the $\ddot{I}{€}^0{f}_0(980)$ mass spectrum, there is evidence of $f_1(1285)$ production. By studying the decay $J/\ddot{I}ˆ\to \ddot{I}•\hat{I}{\cdot }^{\prime }$, the branching fractions of $\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}{€}^0$ and $\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^0\ddot{I}{€}^0\ddot{I}{€}^0$, as well as their ratio, are also measured.

10 pages, 10 figures, published in Phys. Rev. D