Update analysis of $\psi (3686)\to p\bar{p}$

Abstract

We present an updated analysis of the angular distribution for $\psi (3686)\to p\bar{p}$ decay, taking into account transverse beam polarization, to investigate potential sources of forward-backward asymmetry and azimuthal modulation beyond the simple $1+\alpha {\cos }^2\theta$ form. We focus on the interference between the $\psi (3686)$ resonance and the two-photon exchange continuum process, as well as the background from initial-state-final-state radiation interference. A maximum-likelihood fit to the $\cos \theta$ distribution of $\psi (3686)\to p\bar{p}$ yields $\alpha =1.00\pm 0.03$, consistent with previous results. Our model predicts a significant $\sin (2\varphi )$ modulation in the azimuthal angle, indicating the influence of transverse beam polarization. These findings motivate future two-dimensional angular analyses to fully disentangle the polarization and interference dynamics in charmonium decays to baryon pairs.