The eta-photon transition form factor

TL;DR

This paper models the eta-photon transition form factor by combining phenomenological and QCD-based approaches, successfully fitting experimental data and highlighting the importance of twist-three contributions at the matching scale.

Contribution

It introduces a hybrid formalism that matches low-energy phenomenology with high-energy QCD evolution using a Distribution Amplitude from the NJL model, improving data description.

Findings

Good fit to experimental data including BaBar results.

Small twist-three contribution at the matching scale improves accuracy.

Model effectively bridges low and high photon virtualities.

Abstract

The eta-photon transition form factor is evaluated in a formalism based on a phenomenological description at low values of the photon virtuality, and a QCD-based description at high photon virtualities, matching at a scale $Q_{0}^{2}$. The high photon virtuality description makes use of a Distribution Amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars regularization at the matching scale $Q_{0}^{2}$, and QCD evolution from $Q_{0}^{2}$ to higher values of $Q^{2}$. A good description of the available data is obtained. The analysis indicates that the recent data from the BaBar collaboration on pion and eta transition form factor can be well reproduced, if a small contribution of twist three at the matching scale $Q_{0}^{2}$ is included.