Precision Measurement of Neutral Pion Lifetime*

As the lightest and the simplest hadronic particle, π⁰ plays a crucial role in understanding the symmetries of QCD at low-energy. The π⁰→γγ decay width offers a fundamental test of the QCD predictions based on the chiral anomaly and spontaneous chiral symmetry breaking. The theoretical calculations over the past two decades have reached 1% precision in the decay amplitude of the π⁰ into two photons. The experimental measurement of this parameter with a comparable accuracy will provide a stringent test of QCD. The PrimEx collaboration at Jefferson Lab has developed and performed two experiments (PrimEx I &II) to measure the π⁰ radiative decay width via the Primakoff effect. The published final result achieved  a 1.5% total uncertainty on the neutral pion lifetime, the most precise result for this fundamental parameter up to date. The experimental result and its comparison with the theoretical predictions will be discussed.