First observation of $\eta(1405)$ decays into $f_0(980)\pi^0$

Abstract

The decays $J/\psi\rightarrow\gamma\pi^+\pi^-\pi^0$ and $J/\psi\rightarrow\gamma\pi^0\pi^0\pi^0$ are analyzed using a sample of $225\times10^6$ $J/\psi$ events collected with the BESIII detector. The decay of $\eta(1405)$→$f_0(980)\pi^0$ with a large isospin violation is observed for the first time. The width of the $f_0(980)$ observed in the dipion mass spectra is anomalously narrower than the world average. Decay rates for three-pion decays of the $\eta^′$ are also measured precisely.