Neutral Pion Lifetime Measurements and the QCD Chiral Anomaly

Abstract

A fundamental property of QCD is the presence of the chiral anomaly, which is the primary component of the $π^0\rightarrowγγ$ decay amplitude. Based on this anomaly and its small ($\simeq$ 4.5%) chiral correction, a firm prediction of the $π^0$ lifetime can be used as a test of QCD at confinement scale energies. The interesting experimental and theoretical histories of the $π^0$ meson are reviewed, from discovery to the present era. Experimental results are in agreement with the theoretical prediction, within the current ($\simeq$ 3%) experimental error; however, they are not yet sufficiently precise to test the chiral corrected result, which is a firm QCD prediction and is known to $\simeq$ 1% uncertainty. At this level there exist experimental inconsistencies, which require attention. Possible future work to improve the present precision is suggested.