Speaker
Prof.
Liping Gan
(University of North Carolina Wilmington)
Description
As the lightest and the simplest hadronic particle, the neutral pion 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 fundamental 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 result from the first experiment (PrimEx-I) reached 2.8% in the total uncertainty that has led to an improvement of the average value in Particle Data Group by more than a factor of two and half. Data analysis for the second experiment (PrimEx-II) is recently completed with significantly improved precision than the PrimEx-I result. The final PrimEx result has reached 1.5% accuracy in the π0→γγ decay width. This result agrees to the chiral anomaly prediction and is 2σ lower than the high order low-energy QCD predictions. The details of the PrimEx experiment and the physics impacts will be discussed.
Primary author
Prof.
Liping Gan
(University of North Carolina Wilmington)
