Speaker
Description
A critical test for low-energy QCD is the decay of the neutral pion. Comparing this analytic prediction with measured data thus provides a valuable test for low energy QCD and symmetry breaking. The lifetime of the $\pi^0$ can be measured using exclusive $\pi^0$ photoproduction in the Coulomb field of a nucleus, referred to as the Primakoff effect. Using this technique, the PrimEx-I and II experiments found a combined radiative width measurement of 7.806 ± 0.117 eV, which agrees with the chiral anomaly prediction within 0.72%, however there is tension with NLO calculations at the level of 2 standard deviations. Exclusive π0 and η photoproduction were observed during the Charged Pion Polarizability experiment at JLab’s Hall D, which utilized a linearly polarized 4.3-12 GeV photon beam incident on a $^{208}$Pb target. Exclusive $\pi^0$ and $\eta$ photoproduction yields between 0-2.5° lab angle have been extracted from the data. The yields are then fitted with theoretical terms convoluted with the angular resolution and experimental acceptance, π0 decay widths are extracted, and compared with the PrimEx results. We also present the first measurement of the linear polarization asymmetry for $\pi^0$ photoproduction in the Primakoff region, which is sensitive to nuclear incoherent processes and non-pseudoscalar backgrounds.