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arXiv · 1403.3386

Muon decay spin asymmetry

Fabrizio Caola·Andrzej Czarnecki·Yi Liang·Kirill Melnikov·Robert Szafron
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Abstract

We compute the spin asymmetry of the muon decay through O(alpha^2) in perturbative QED. These two-loop corrections are about a factor five (twenty) smaller than the current statistical (systematic) uncertainty of the most precise measurement, performed by the TWIST collaboration. We point out that at O(alpha^2) the asymmetry requires a careful definition due to multi-lepton final states and suggest to use familiar QCD techniques to define it in an infra-red safe way. We find that the TWIST measurement of the asymmetry is in excellent agreement with the Standard Model.

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Fabrizio Caola, Andrzej Czarnecki, Yi Liang, Kirill Melnikov, Robert Szafron. 2014-03-13. Muon decay spin asymmetry. https://doi.org/10.1103/physrevd.90.053004

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