Analysis of the J/psi --> pi^0 gamma^* transition form factor

TL;DR

This paper uses dispersion theory to analyze the J/psi to pi^0 gamma^* transition form factor, emphasizing the role of light-quark states and providing predictions for future experimental validation.

Contribution

It introduces a dispersion-theoretic approach to predict the J/psi transition form factor, highlighting the dominance of light-quark contributions and estimating multi-pion and charmonium effects.

Findings

Light-quark degrees of freedom dominate the spectral function.

Two-pion intermediate states are significant.

Predicted form factor can be tested in future experiments.

Abstract

In view of the first measurement of the branching fraction for J/psi --> pi^0 e^+ e^- by the BESIII collaboration, we analyze what can be learnt on the corresponding transition form factor using dispersion theory. We show that light-quark degrees of freedom dominate the spectral function, in particular two-pion intermediate states. Estimating the effects of multi-pion states as well as charmonium, we arrive at a prediction for the complete form factor that should be scrutinized experimentally in the future.