Precision Study of $\eta^\prime\rightarrow\gamma\pi^+\pi^-$ Decay Dynamics

Abstract

Using a low background data sample of $9.7×10^5$ $J\psi\rightarrow\gamma\eta^\prime$, $\eta^\prime\rightarrow\gamma\pi^+\pi^-$ events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of $\eta^\prime\rightarrow\gamma\pi^+\pi^-$ are studied with both model-dependent and model-independent approaches. The contributions of ω and the ρ(770)−ω interference are observed for the first time in the decays $\eta^\prime\rightarrow\gamma\pi^+\pi^-$ in both approaches. Additionally, a contribution from the box anomaly or the ρ(1450) resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.