Precision Measurement of the $\pi^{0\thinspace }$Lifetime via the Primakoff Effect

The neutral pseudoscalar meson$\pi^{\mathrm{0\thinspace }}$plays a fundamental role in QCD at low-energy. The $\pi^{\mathrm{0}}\to \gamma \gamma $decay width offers a sensitive probe for the chiral anomaly and spontaneous chiral symmetry breaking, and the nature of QCD confinement. The theoretical calculations over the last decade have reached 1{\%} precision in the decay amplitude of the $\pi^{\mathrm{0\thinspace }}$into two photons. The experimental measurement of this parameter with a comparable precision will be an important test of QCD. The PrimEx collaboration at Jefferson Lab has developed and performed experiments to measure the$\pi^{\mathrm{0\thinspace }}$radiative decay width via the Primakoff effect. The published result from the first experiment (PrimEx-I) has a 2.8{\%} total uncertainty. The second experiment (PrimEx-II) was performed with the final goal of 1.4{\%} precision. The updated result of PrimEx-II will be presented.