Evidence for a J/psi-ppbar Pauli Strong Coupling ?

TL;DR

This study investigates the J/psi-ppbar couplings, revealing evidence for a significant Pauli component that influences production processes and can be better understood through polarized reaction analysis.

Contribution

It provides the first experimental constraints on the Dirac and Pauli couplings of J/psi to proton-antiproton pairs, highlighting the importance of the Pauli term.

Findings

Data suggests a non-zero Pauli coupling for J/psi-ppbar interaction.

Pure Dirac coupling is inconsistent with recent unpolarized data.

Polarized reactions can resolve phase ambiguities in coupling measurements.

Abstract

The couplings of charmonia and charmonium hybrids (generically Psi) to ppbar are of great interest in view of future plans to study these states using an antiproton storage ring at GSI. These low to moderate energy Psi-ppbar couplings are not well understood theoretically, and currently must be determined from experiment. In this letter we note that the two independent Dirac (gamma_mu) and Pauli (sigma_munu) ppbar couplings of the J/psi and psi' can be constrained by the angular distribution of e+e- -> (J/psi, psi') -> ppbar on resonance. A comparison of our theoretical results to recent unpolarized data allows estimates of the ppbar couplings; in the better determined J/psi case the data is inconsistent with a pure Dirac (gamma_mu) coupling, and can be explained by the presence of a sigma_munu term. This Pauli coupling may significantly affect the cross section of the PANDA process p pbar -> pi0 J/psi near threshold. There is a phase ambiguity that makes it impossible to uniquely determine the magnitudes and relative phase of the Dirac and Pauli couplings from the unpolarized angular distributions alone; we show in detail how this can be resolved through a study of the polarized reactions.