Observation of the isospin-violating decay $J\mathrm{/}\psi \to \varphi {\pi }^0{f}_0(980)$

Using a sample of 1.31 billion $J\mathrm{/}\psi$ 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 $J\mathrm{/}\psi \to \varphi {\pi }^0{f}_0(980)$ 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 $J/\psi \to \phi\eta’$,thebranchingfractionsof$\eta’ \to \pi^{+}\pi^{-}\pi^{0}$and$\eta’ \to \pi^{0}\pi^{0}\pi^{0}$, as well as their ratio, are also measured.