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High-precision muon decay predictions for ALP searches


Banerjee, Pulak; Coutinho, Antonio; Engel, Tim; Gurgone, Andrea; Signer, Adrian; Ulrich, Yannick (2023). High-precision muon decay predictions for ALP searches. SciPost physics, 15:021.

Abstract

We present an improved theoretical prediction of the positron energy spectrum for the polarised Michel decay \mu^+\to e^+ \nu_e\bar{\nu}_\mu. In addition to the full next-to-next-to-leading order correction of order \alpha^2 in the electromagnetic coupling, we include logarithmically enhanced terms at even higher orders. Logarithms due to collinear emission are included at next-to-leading accuracy up to order \alpha^4. At the endpoint of the Michel spectrum, soft photon emission results in large logarithms that are resummed up to next-to-next-to-leading logarithmic accuracy. We apply our results in the context of the MEG II and Mu3e experiments to estimate the impact of the theory error on the branching ratio sensitivity for the lepton-flavour-violating decay \mu^+\to e^+ X of a muon into an axion-like particle X.

Abstract

We present an improved theoretical prediction of the positron energy spectrum for the polarised Michel decay \mu^+\to e^+ \nu_e\bar{\nu}_\mu. In addition to the full next-to-next-to-leading order correction of order \alpha^2 in the electromagnetic coupling, we include logarithmically enhanced terms at even higher orders. Logarithms due to collinear emission are included at next-to-leading accuracy up to order \alpha^4. At the endpoint of the Michel spectrum, soft photon emission results in large logarithms that are resummed up to next-to-next-to-leading logarithmic accuracy. We apply our results in the context of the MEG II and Mu3e experiments to estimate the impact of the theory error on the branching ratio sensitivity for the lepton-flavour-violating decay \mu^+\to e^+ X of a muon into an axion-like particle X.

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Additional indexing

Item Type:Journal Article, not_refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > General Physics and Astronomy
Uncontrolled Keywords:General Physics and Astronomy
Language:English
Date:21 July 2023
Deposited On:27 Dec 2023 12:07
Last Modified:28 Jun 2024 03:31
Publisher:SciPost
ISSN:2542-4653
OA Status:Gold
Publisher DOI:https://doi.org/10.21468/scipostphys.15.1.021
Project Information:
  • : FunderH2020
  • : Grant ID701647
  • : Project TitlePSI-FELLOW-II-3i - International, Interdisciplinary and Intersectoral Postdocs
  • : FunderSNSF
  • : Grant ID207386
  • : Project TitlePrecision calculations for lepton scattering
  • Content: Published Version
  • Language: English
  • Licence: Creative Commons: Attribution 4.0 International (CC BY 4.0)