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

Abstract

We present an updated analysis of the angular distribution for $ψ(3686) \to p\bar{p}$ decay, taking into account transverse beam polarization, to investigate potential sources of forward-backward asymmetry and azimuthal modulation beyond the simple $1+α\cos^2θ$ form. We focus on the interference between the $ψ(3686)$ 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 $\cosθ$ distribution of $ψ(3686)\to p\bar{p}$ yields $α= 1.00 \pm 0.03$, consistent with previous results. The fitted contributions from the two-photon interference are small but non-negligible, while the ISR-FSR background is negligible. Our model predicts a significant $\sin(2φ)$ 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.

Figures (7)

• Figure 1: Feynman diagrams of one (a,b) and two (c,d) virtual photon processes $e^+e^-\to\gamma^*/\psi(3686)$ or $\gamma^*\gamma^*\to p\bar{p}$
• Figure 2: Asymmetric proton angular distribution resulting from the interference between resonance and two-photon processes.
• Figure 3: Tree level of Feynman diagrams for ISR (a), FSR (b) processes $e^+e^-\to\psi(3686)\to p\bar{p}$.
• Figure 4: Asymmetric proton angular distribution resulting from the interference between ISR and FSR processes.
• Figure 5: The plot of $\cos\theta_{p}$ distribution. The contribution of the interference with two-photon exchange process is shown by a azure line, the contribution of initial state radiation and final state radiation interference is shown by a light blue line. The total PDF is shown by a red line. (b) shows the detail of distributions of the interference terms.