TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.15.1.021
TI  - High-precision muon decay predictions for ALP searches
PY  - 2023/07/21
UR  - https://scipost.org/SciPostPhys.15.1.021
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 15
IS  - 1
SP  - 021
A1  - Banerjee, Pulak
AU  - Coutinho, Antonio
AU  - Engel, Tim
AU  - Gurgone, Andrea
AU  - Signer, Adrian
AU  - Ulrich, Yannick
AB  - 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 $X$.
ER  -

@Article{10.21468/SciPostPhys.15.1.021,
	title={{High-precision muon decay predictions for ALP searches}},
	author={Pulak Banerjee and  Antonio Coutinho and  Tim Engel and Andrea Gurgone and Adrian Signer and Yannick Ulrich},
	journal={SciPost Phys.},
	volume={15},
	pages={021},
	year={2023},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.15.1.021},
	url={https://scipost.org/10.21468/SciPostPhys.15.1.021},
}