High-precision muon decay predictions for ALP searches

Banerjee, Pulak; Coutinho, Antonio; Engel, Tim; Gurgone, Andrea; Signer, Adrian; Ulrich, Yannick

Abstract

We present an improved theoretical prediction of the positron energy spectrum for the polarised Michel decay μ+→e+νe¯νμ. In addition to the full next-to-next-to-leading order correction of order α2 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 α4. 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 μ+→e+X of a muon into an axion-like particle X.

Citation

Banerjee, P., Coutinho, A., Engel, T., Gurgone, A., Signer, A., & Ulrich, Y. (2023). High-precision muon decay predictions for ALP searches. SciPost Physics, 15(1), Article 021. https://doi.org/10.21468/scipostphys.15.1.021

• Journal Article Type: Article
• Acceptance Date: May 22, 2023
• Online Publication Date: Jul 21, 2023
• Publication Date: Jul 21, 2023
• Deposit Date: Feb 19, 2024
• Publicly Available Date: Feb 19, 2024
• Journal: SciPost Physics
• Print ISSN: 2542-4653
• Electronic ISSN: 2542-4653
• Publisher: SciPost
• Peer Reviewed: Peer Reviewed
• Volume: 15
• Issue: 1
• Article Number: 021
• DOI: https://doi.org/10.21468/scipostphys.15.1.021
• Keywords: General Physics and Astronomy
• Public URL: https://durham-repository.worktribe.com/output/2269825