Observation of $a^{0}_{0}(980)$−$f_{0}(980)$ Mixing

We report the first observation of $a^{0}_{0}(980)$−$f_{0}(980)$ mixing in the decays of $J/\psi\to\phi f_{0}(980)\to\phi a^{0}_{0}(980)\to\phi\eta\pi^{0}$ and $\chi_{c1}\to a^{0}_{0}(980)\pi^{0}\to f_{0}(980)\pi^{0}\to\pi^{+}\pi^{-}\pi^{0}$, using data samples of $1.31×10^9 J/\psi$ events and $4.48×10^8 \psi(3686)$ events accumulated with the BESIII detector. The signals of f0(980)→a00(980) and a00(980)→f0(980) mixing are observed at levels of statistical significance of 7.4σ and 5.5σ, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, $g_{a_{0}K^{+}K^{-}}$ and $g_{f_{0}K^{+}K^{-}}$, are estimated. The results improve the understanding of the nature of $a^{0}_{0}(980)$ and $f_{0}(980)$