scholarly journals Real Photon to Neutral Pion Ratios and Photon-Jet Correlations in Quantum Chromodynamics

1980 ◽  
Vol 64 (1) ◽  
pp. 230-257 ◽  
Author(s):  
K. Kato ◽  
H. Yamamoto
Keyword(s):  
Quantum Chromodynamics ◽  
Neutral Pion ◽  
Real Photon

scholarly journals Precision measurement of the neutral pion lifetime

Science ◽  
2020 ◽  
Vol 368 (6490) ◽  
pp. 506-509 ◽  
Author(s):  
I. Larin ◽  
Y. Zhang ◽  
A. Gasparian ◽  
L. Gan ◽  
R. Miskimen ◽  
...  
Keyword(s):  
Quantum Chromodynamics ◽  
Cross Sections ◽  
Differential Cross ◽  
Precision Measurement ◽  
Neutral Pion ◽  
Weighted Average ◽  
Chiral Anomaly ◽  
Statistical Uncertainty ◽  
Total Uncertainty ◽  
Axial Anomaly

The explicit breaking of the axial symmetry by quantum fluctuations gives rise to the so-called axial anomaly. This phenomenon is solely responsible for the decay of the neutral pion π0 into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of the π0→ γγ process. The differential cross sections for π0 photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yielding Γ(π0→ γγ)=7.798±0.056(stat.)±0.109(syst.) eV, where stat. denotes the statistical uncertainty and syst. the systematic uncertainty. We combined the results of this and an earlier experiment to generate a weighted average of Γ(π0→ γγ)=7.802±0.052(stat.)±0.105(syst.) eV. Our final result has a total uncertainty of 1.50% and confirms the prediction based on the chiral anomaly in quantum chromodynamics.

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