High-precision muon decay predictions for ALP searches
Pulak Banerjee, Antonio Coutinho, Tim Engel, Andrea Gurgone, Adrian Signer, Yannick Ulrich
SciPost Phys. 15, 021 (2023) · published 21 July 2023
- doi: 10.21468/SciPostPhys.15.1.021
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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 $X$.
Cited by 5
Authors / Affiliations: mappings to Contributors and Organizations
See all Organizations.- 1 2 Pulak Banerjee,
- 3 4 Antonio Coutinho,
- 3 5 6 Tim Engel,
- 7 8 Andrea Gurgone,
- 3 6 Adrian Signer,
- 9 Yannick Ulrich
- 1 浙江大学 / Zhejiang University [ZJU]
- 2 भारतीय प्रौद्योगिकी संस्थान गुवाहाटी / Indian Institute of Technology Guwahati [IITG]
- 3 Paul Scherrer Institute [PSI]
- 4 Universitat de València / University of Valencia [UV]
- 5 Albert-Ludwigs-Universität Freiburg / University of Freiburg
- 6 Universität Zürich / University of Zurich [UZH]
- 7 Università degli Studi di Pavia / University of Pavia [UNIPV]
- 8 INFN Sezione di Pavia
- 9 Durham University