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Title: Precision measurement of the neutral pion lifetime

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 π0into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of theπ0 γγprocess. The differential cross sections for π0photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yieldingΓ(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 ofΓ(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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p. 506-509
American Association for the Advancement of Science (AAAS)
Sponsoring Org:
National Science Foundation
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