The problems of $\eta'\rightarrow\pi^0\gamma\gamma$ decay and the New Physics

Abstract

Rare decays of light mesons may be a discovery window for a new weakly coupled forces hidden at low energy QCD scale. BES-III Collaboration reported the observation of the rare decay $\eta'\rightarrow\pi^0\gamma\gamma$. The observed decay width disagrees with the preliminary theoretical estimations. We show that this tension may be attributed to the New Physics, presumably Dark Photon. For completeness, we consider the possible influence of the New Physics on a similar well-measured decay $\eta\rightarrow\pi^0\gamma\gamma$ and a recently measured one $\eta' \rightarrow \eta\gamma\gamma$ and show that the impact of the hypothetical Dark Photon may be also present in these decays also.