Measuring the Neutral Pion Polarizability

This proposal presents our plan to make a precision measurement of the cross section for γγ → π0π0 via the Primakoff effect using the GlueX detector in Hall D. The aim is to significantly improve the data in the low π0π0 invariant mass domain, which is essential for understanding the low energy regime of Compton scattering on the π0. In particular, the aim is to obtain a first accurate experimental determination of the neutral pion polarizability απ − βπ, which is one of the important predictions of chiral perturbation theory and a key test of chiral dynamics on the π0. Our goal is to measure σ(γγ → π0π0) to a precision of ∼1%, which would determine the combination of απ0−βπ0 to a precision of 10%. We expect this experiment to run concurrently with the previously approved experiment to measure the charged pion polarizability (CPP) [1] in Hall D.