The neutral pion is the lightest two-quarks strongly interacting particle in Nature. As such, the properties of π0 decay are especially sensitive to the underlying fundamental symmetries of quantum chromodynamics (QCD). In particular, the π0 →γγ decay width is primarily defined by the braking effects of axial and chiral symmetries (chiral anomaly) in QCD. Theoretical activities in this domain over the last years resulted in small corrections to the anomaly with a percent level accuracy for the π0→γγ decay width. The PrimEx collaboration at Jefferson Laboratory has developed and performed two new experiments to measure the π0 →γγ decay width with high precision using the Primakoff effect. The combined result from two experiments: Γ(π0→γγ) = 7.802±0.052(stat.) ±0.105(syst.) eV was recently published in the Science journal. With its 1.50% total uncertainty it represents the most accurate measurement of this fundamental quantity to date. The results of these experiments together with the experimental method will be presented and discussed in this talk.
|Collaboration||PrimEx at Jefferson Lab|