### Speaker

Ashot Gasparian
(North Carolina A&T State University, Greensboro)

### Description

The neutral pion is the lightest strongly interacting particle in Nature. Therefore, the properties of $\pi^0$ decay are especially sensitive to the underlying fundamental symmetries of quantum chromodynamics (QCD). In particular, the pi^0 -> gamma gamma decay width is primarily defined by the spontaneous chiral symmetry breaking effect (chiral anomaly) in QCD. Theoretical activities in this domain over the past several years have resulted in a high precision (1% level) prediction for the pi^0 -> gamma gamma decay width. The PrimEx collaboration at Jefferson Lab has developed and performed two new experiments to measure the pi^0 -> gamma gamma decay width with high precision using the Primakoff effect. The published result from the first experiment (PrimEx-I), Gamma(pi^0 -> gamma gamma) = 7.82+- 0.14 (stat) +- 0.17 (syst) eV, is a factor of 2.1 more precise than the currently accepted value, and it is in agreement with the chiral anomaly prediction. The second experiment (PrimEx-II) was performed in 2010 with a goal of 1.4% total uncertainty to address the next-to-leading-order chiral perturbation theory calculations. The preliminary results from the PrimEx-II experiment will be presented in this talk.

### Primary author

Ashot Gasparian
(North Carolina A&T State University, Greensboro)