In:
Science, American Association for the Advancement of Science (AAAS), Vol. 368, No. 6490 ( 2020-05), p. 506-509
Abstract:
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 π 0 into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of the π 0 → γ γ process. The differential cross sections for π 0 photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yielding Γ ( π 0 → γ γ ) = 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 ( π 0 → γ γ ) = 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.
Type of Medium:
Online Resource
ISSN:
0036-8075
,
1095-9203
DOI:
10.1126/science.aay6641
Language:
English
Publisher:
American Association for the Advancement of Science (AAAS)
Publication Date:
2020
detail.hit.zdb_id:
128410-1
detail.hit.zdb_id:
2066996-3
detail.hit.zdb_id:
2060783-0
SSG:
11
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