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 dominant component of the ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ decay rate. Based on this anomaly and its small ($\ensuremath{\simeq}4.5%$) chiral correction, a prediction of the ${\ensuremath{\pi}}^{0}$ lifetime can be used as a test of QCD at confinement scale energies. The interesting experimental and theoretical histories of the ${\ensuremath{\pi}}^{0}$ meson are reviewed, from discovery to the present era. Experimental results are in agreement with the theoretical prediction, within the current ($\ensuremath{\simeq}3%$) 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 $\ensuremath{\simeq}1%$ uncertainty. At this level there exist experimental inconsistencies, which require attention. Possible future work to improve the present precision is suggested.