Study ofη→π0γγdecay using the quark-box diagram

We study the decay of $\eta$ mesons into ${\pi }^0$ and a photon pair via the quark-box mechanism in a phenomenological quark model. The main parameters of the model are the $\eta \mathrm{qq}$ and $\pi \mathrm{qq}$ couplings, which are fixed by the $\eta \to \gamma \gamma$ and ${\pi }^0\to \gamma \gamma$ decays. With constituent quark masses of 300 MeV for $u$ and $d$ quarks we find the width to be 0.70 eV, in good agreement with the experimental value of 0.84±0.18 eV. In contrast, chiral perturbation theory gives a width of 0.42 eV. A detailed comparison with the vectormeson dominance model is also given.