A quark model calculation of the processes γγ→π+π- and γγ→π0π0 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 γγ→π0π0 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 π+π- cross section is in good agreement with experiment, while the π0π0 cross section is in qualitative agreement with the data.

Physical Review C - Nuclear Physics
Department of Physics

Blundell, H.G., Godfrey, S, Hay, G., & Swanson, E.S. (2000). A quark model calculation of γγ→ππ including final-state interactions. Physical Review C - Nuclear Physics, 61(2), 252031–252037.