Neutral Pion Lifetime Measurements and the QCD Chiral Anomaly

TL;DR

This paper reviews the measurement of the neutral pion lifetime as a test of QCD's chiral anomaly, highlighting current experimental agreement with theory but noting the need for more precise measurements to resolve existing inconsistencies.

Contribution

It summarizes the history and current status of neutral pion lifetime measurements and discusses the importance of improved precision for testing QCD predictions.

Findings

Experimental results agree with theoretical predictions within 3% error.

Current measurements are not precise enough to test the 1% chiral correction.

Experimental inconsistencies exist that need resolution.

Abstract

A fundamental property of QCD is the presence of the chiral anomaly, which is the primary component of the $\pi^0\rightarrow\gamma\gamma$ decay amplitude. Based on this anomaly and its small ($\simeq$ 4.5%) chiral correction, a firm prediction of the $\pi^0$ lifetime can be used as a test of QCD at confinement scale energies. The interesting experimental and theoretical histories of the $\pi^0$ 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.