A Precision Measurement of Neutral Pion Lifetime

Thesis/Dissertation · Tue May 01 04:00:00 EDT 2018

OSTI ID:2572052

Zhang, Yang ^[1]

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1. Duke Univ., Durham, NC (United States)

The neutral pion decays via chiral anomaly and this process historically led to the discovery of the chiral anomaly. The p 0 decay width is among the most precise predictions of quantum chromodynamics (QCD) at low energy. However, the current experimental results are not commensurate with theoretical predictions. The Particle Data Group (PDG) average of the experimental results is 7.63  0.16 eV, which is consistent with the chiral anomaly prediction (7.725  0.044 eV). Recent theoretical calculations based on the sum rule and chiral perturbation theories (ChPT) show an increase of 3.0%-4.5% to the chiral anomaly prediction with 1% precision. As a result, a precise measurement of the neutral pion decay width would be one of the most stringent tests of low energy QCD. PrimEx-II experiment measured the neutral pion decay width via the Primakoff effect using two targets, silicon and 12C. The p 0 decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting total p 0 decay width is 7.82  0.05pstatq  0.10psystq eV. With a total uncertainty of 1.8%, this result is the most precise experimental estimation. The PrimEx-II result lies within 0.8 s above the chiral anomaly predition, one s below the sum rule prediction, and 1.8 s below the ChPT calculations. This result is in better agreement with the chiral anomaly prediction.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 2572052
• Report Number(s): DOE/OR/23177-7923; JLAB-PHY-25-4384
• Country of Publication: United States
• Language: English