On the physical Relevance of the Study of gamma* gamma -> pi0 pi0 at small t and large Q2

TL;DR

This paper explores the potential of measuring gamma* gamma -> pi0 pi0 at small t and large Q2 to access the neutral pion axial form factor using QCD calculations with Transition Distribution Amplitudes, which could be achieved at existing colliders.

Contribution

It proposes a novel experimental approach to measure the neutral pion axial form factor through exclusive pi0 pair production in gamma* gamma scattering at high-energy colliders.

Findings

The process can be described using Transition Distribution Amplitudes linked to the pion axial form factor.

Measurement at colliders like CLEO, KEK-B, and PEP-II can provide new insights into pion structure.

Theoretical framework connects exclusive reaction rates to fundamental QCD form factors.

Abstract

We discuss the relevance of a dedicated measurement of exclusive production of a pair of neutral pions in a hard gamma* gamma scattering at small momentum transfer. In this case, the virtuality of one photon provides us with a hard scale in the process, enabling us to perform a QCD calculation of this reaction rate using the concept of Transition Distribution Amplitudes (TDA). Those are related by sum rules to the pion axial form factor F^pi_A and, as a direct consequence, a cross-section measurement of this process at intense beam electron-positron colliders such as CLEO, KEK-B and PEP-II, or Super-B would provide us with a unique measurement of the neutral pion axial form factor F^pi0_A at small scale.