Observation of the isospin-violating decay $J/\psi \to \phi\pi^{0}f_{0}(980)$

TL;DR

This paper reports the first observation of the isospin-violating decay $J/ar{ ext{}}$\psi \to \phi \pi^{0} f_{0}(980)$ using a large sample of $J/\psi$ events, revealing a narrower $f_{0}(980)$ width and evidence of $f_1(1285)$ production.

Contribution

It presents the first observation of the isospin-violating decay $J/\psi \to \phi \pi^{0} f_{0}(980)$ and measures the $f_{0}(980)$ width and related decay properties.

Findings

First observation of the decay $J/\psi \to \phi \pi^{0} f_{0}(980)$

$f_{0}(980)$ width is smaller than the world average

Evidence of $f_1(1285)$ production in the spectrum

Abstract

Using a sample of 1.31 billion $J/\psi$ events collected with the BESIII detector at the BEPCII collider, the decays $J/\psi \to \phi \pi^{+}\pi^{-}\pi^{0}$ and $J/\psi \to \phi \pi^{0}\pi^{0}\pi^{0}$ are investigated. The isospin violating decay $J/\psi \to \phi \pi^{0} f_{0}(980)$ with $f_{0}(980) \to \pi\pi$, 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 $\pi^{0} f_{0}(980)$ mass spectrum, there is evidence of $f_1(1285)$ production. By studying the decay $J/\psi \to \phi\eta'$, the branching fractions of $\eta' \to \pi^{+}\pi^{-}\pi^{0}$ and $\eta' \to \pi^{0}\pi^{0}\pi^{0}$, as well as their ratio, are also measured.