The Neutral Pion Life Time: Final Result from the PrimEx Experiments

The neutral pion is the lightest strongly interacting particle in Nature. Therefore, the properties of π⁰ decay are especially sensitive to the underlying fundamental symmetries of quantum chromodynamics (QCD). In particular, the π⁰ decay width is primarily defined by the chiral anomaly, a fundamental symmetry breaking effect in QCD. Theoretical activities in this domain over the last years resulted in a high precision (1% level) prediction for the π⁰ decay width. The PrimEx collaboration at Jefferson Lab has developed and performed two new experiments to measure the π⁰ decay width with high precision using the Primakoff effect. The published result from the first experiment (PrimEx-I) was a factor of two more precise than the PDG accepted average value, and was in a good 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 final results from the PrimEx experiments will be presented and discussed in this talk.