Muon decay in orbit: spectrum of high-energy electrons

TL;DR

This paper analyzes the spectrum of high-energy electrons from muon decay in orbit to better understand background signals in rare muon-to-electron conversion experiments, aiding future searches for new physics.

Contribution

It provides a detailed analysis of Coulombic-bound-state muon decay, including nuclear recoil effects, to improve background modeling in upcoming experiments.

Findings

Characterized the background electron spectrum from muon decay in orbit.

Assessed the impact of nuclear recoil on decay spectrum shape.

Discussed implications for future lepton-flavor-violation searches.

Abstract

Experimental searches for lepton-flavor-violating coherent muon-to-electron conversion in the field of a nucleus, have been proposed to reach the unprecedented sensitivity of 10^(-16) - 10^(-18) per stopped muon. At that level, they probe new interactions at effective-mass scales well beyond 1000 TeV. However, they must contend with background from ordinary bound muon decay. To better understand the background-spectrum shape and rate, we have carried out a detailed analysis of Coulombic-bound-state muon decay, including nuclear recoil. Implications for future experiments are briefly discussed.