A Measurement of Proton, Deuteron, Triton and Alpha Particle Emission after Nuclear Muon Capture on Al, Si and Ti with the AlCap Experiment

TL;DR

The AlCap experiment measured the yields and energy spectra of various charged particles emitted after muon capture on Al, Si, and Ti, providing essential background data for muon-to-electron conversion experiments.

Contribution

This work provides detailed measurements of charged particle emissions after muon capture on multiple nuclei, crucial for background understanding in upcoming precision experiments.

Findings

Yields and energy spectra for protons, deuterons, tritons, and alpha particles are reported.

Charged particle types were identified and their energy distributions unfolded.

Results inform background modeling for muon-to-electron conversion searches.

Abstract

Heavy charged particles after nuclear muon capture are an important nuclear physics background to the muon-to-electron conversion experiments Mu2e and COMET, which will search for charged lepton flavor violation at an unprecedented level of sensitivity. The AlCap experiment measured the yield and energy spectra of protons, deuterons, tritons, and alpha particles emitted after the nuclear capture of muons stopped in Al, Si, and Ti in the low energy range relevant for the muon-to-electron conversion experiments. Individual charged particle types were identified in layered silicon detector packages and their initial energy distributions were unfolded from the observed energy spectra. Detailed information on yields and energy spectra for all observed nuclei are presented in the paper.