6533b858fe1ef96bd12b628b

RESEARCH PRODUCT

η→π0γγdecay within a chiral unitary approach

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We improve the calculations of the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\eta}}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ decay within the context of meson chiral Lagrangians. We use a chiral unitary approach for the meson-meson interaction, thus generating the ${a}_{0}(980)$ resonance and fixing the long standing sign ambiguity on its contribution. This also allows us to calculate the loops with one vector meson exchange, thus removing a former source of uncertainty. In addition we ensure the consistency of the approach with other processes, first, by using vector meson dominance couplings normalized to agree with radiative vector meson decays and, second, by checking the consistency of the calculations with the related $\ensuremath{\gamma}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}{\ensuremath{\pi}}^{0}\ensuremath{\eta}$ reaction. We find an $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\eta}}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ decay width of $0.47\ifmmode\pm\else\textpm\fi{}0.10\mathrm{eV},$ in clear disagreement with published data but in remarkable agreement with the most recent measurement.