Study of the isospin breaking decay $\mathbf{Y}(2175)\to \mathbf{\varphi }{\mathbf{f}}_0(980)\to \mathbf{\varphi \eta }{\mathbf{\pi }}^0$ at BESIII

Abstract

Using measured branching fraction of the decay $J/\psi \to \eta Y(2175))\to \eta \varphi f_0(980)\to \eta \varphi {\pi }^{+}{\pi }^{-}$ from the BESIII experiment, we estimate branching fraction of $J/\psi \to \eta Y(2175))\to \eta \varphi f_0(980)\to \eta \varphi \eta {\pi }^0$ decay, which proceeds via the $f_0(980)$-$a_0^0(980)$ mixing and the ${\pi }^0$-$\eta$ mixing. The branching fraction is predicted to be about $O(10^{-6})$, which can be accessed with $10^{10}$ $J/\psi$ events collected at the BESIII. The decay is dominated by the contribution from $f_0(980)$-$a_0^0(980)$ mixing. We find that the interference between the amplitudes due to $f_0(980)$-$a_0^0(980)$ mixing and that due to ${\pi }^0$-$\eta$ mixing is destructive. The branching fraction can be decreased by about $10\%$ owing to the interference effect. We also study the $\eta {\pi }^0$ mass squared spectrum, and find that a narrow peak due to the $f_0(980)$-$a_0^0(980)$ mixing in the $\eta {\pi }^0$ mass squared spectrum should be observed. The observation of this decay in experiment will be helpful to determine the $f_0(980)$-$a_0^0(980)$ mixing intensity and get information about the structures of the light scalar mesons.

Comments: 16 pages, 3 figures