A Quark Model Calculation of gamma gamma to pi pi Including Final State Interactions

TL;DR

This paper uses a quark model to calculate gamma gamma to pi pi processes, showing that final state interactions induce a neutral pion production cross section consistent with experimental observations.

Contribution

It introduces a method to account for neutral pion production via isospin rotation caused by final state interactions in a quark model framework.

Findings

Pi+ pi- cross section matches experimental data

Pi0 pi0 cross section is qualitatively consistent with data

Final state interactions explain neutral pion production

Abstract

A quark model calculation of the processes gamma gamma -> pi+ pi- and gamma gamma -> pi0 pi0 is performed. At tree level, only charged pions couple to the initial state photons and neutral pions are not expected in the final state. However, a small but significant gamma gamma -> pi0 pi0 cross section is observed. We demonstrate that this may be accounted for by a rotation in isospin space induced by final state interactions. The resulting pi+ pi- cross section is in good agreement with experiment while the pi0 pi0 cross section is in qualitative agreement with the data.