Speaker
Description
We present a theoretical analysis of the doubly radiative decays $\eta^{(\prime)}\to\pi^{0}\gamma\gamma$ and $\eta^{\prime}\to\eta\gamma\gamma$, including vector, scalar, and tensor meson exchange contributions. Vector meson dominance and the linear sigma model are used for vector and scalar exchanges, while the $a_{2}(1320)$ tensor meson is incorporated within a chiral framework. Vector meson exchange dominates all three channels.
For the $\eta\to\pi^{0}\gamma\gamma$ decay, the tensor meson contribution is small, but its destructive interference with the vector amplitude reduces the decay width by about $14\%$, bringing our prediction into excellent agreement with the recent KLOE-2 measurement. In $\eta^{\prime}\to\pi^{0}\gamma\gamma$, the tensor contribution is negligible, as the decay is largely saturated by the on-shell $\omega$ resonance.
For $\eta^{\prime}\to\eta\gamma\gamma$, scalar exchanges, especially the $\sigma(500)$, provide a sizeable contribution, making this channel a potential probe of the properties of this still poorly understood resonance. Our results provide a unified description of these decays and emphasize the phenomenological impact of vector–tensor interference in the $\eta\to\pi^{0}\gamma\gamma$ channel.
