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| Main Authors: | , , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2510.00787 |
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Table of Contents:
- In light of the recent measurement of the $η\toπ^{0}γγ$ decay by the KLOE-2 Collaboration, a previous analysis including vector- and scalar-meson exchange contributions using the VMD and L$σ$M frameworks, respectively, is extended in the present study to incorporate the effects of the $a_{2}(1320)$ tensor meson within a chiral context. Although the individual contribution of the $a_{2}$ is negligible, its destructive interference with the vector-meson resonances is found to be significant, representing approximately $18\%$ of the total signal and substantially affecting the diphoton invariant-mass distribution, especially at low $m_{γγ}^{2}$ values. The total decay rate is calculated to be $Γ(η\toπ^{0}γγ)=0.154(22)$ eV, which corresponds to a branching ratio of ${\rm BR}(η\toπ^{0}γγ)=1.17(17)\times10^{-4}$. This result is approximately $5σ$ below the reported value of the PDG, $2.55(22)\times10^{-4}$, while it is in very good agreement with the KLOE-2 measurement, $0.98(11_{\rm stat})(14_{\rm syst})\times10^{-4}$. In contrast, the total contribution of the $a_{2}$ is found to be negligible in $η^{\prime}\toπ^{0}γγ$, as this process is completely dominated by the exchange of an on-shell $ω$ vector resonance.