Direct measurement of the lifetime of the neutral pion

Abstract The lifetime of the neutral pion ( π 0 ) has been directly measured. The lifetime has been found to be τ π 0 = (0.897±0.022±0.017) × 10 −16 s. The systematic error results from uncertainties in the momentum spectrum of the π 0 used for the measurement. This measurement yields a decay width of the π 0 of (7.34±0.18±0.11) eV. An axial anomaly calculation, which neglects the finite mass of the π 0 , predicts a value of 7.87 eV.