Neutron Emission Following Nuclear Muon Capture in Al

Date

2018-12

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Abstract

The Mu2e collaboration is designing an experiment which will search for the forbidden decay μ− + Al-27 → e− + Al-27 with a single-event sensitivity of 3 × 10^−17 , an improvement of four orders of magnitude beyond the current limit set by the SINDRUM II collaboration. Achieving this sensitivity requires a thorough understanding of the backgrounds and competing interactions. Therefore, the AlCap collaboration was formed to study particle emissions from μ− + Al-27 → νμ + M g-27. This dissertation will present the results of the neutron emissions from this study, and includes a measurement of the muon lifetime when captured by Al, Ti, and Pb with results of 864 ± 2, 341 ± 1, and 78 ± 1 ns, respectively. Neutron recoils are measured using two BC501a detectors by removing gamma interactions using an integrated charge comparison method for pulse shape discrimination. The response of the detectors is studied using NRESP7 and Geant4. The neutron emission spectra are unfolded in the energy range from 2 to 12 MeV using Heprow. The resulting spectrum from Al is compared to current simulations used by Mu2e. The rate of neutron emissions for neutrons with an energy between 2 and 12 MeV is determined for these three targets, giving a rate of 0.63 ± 0.04, 0.44 ± 0.03, and 0.56 ± 0.04 neutrons per muon captured for, respectively, Al, Ti and Pb. If the determined evaporation spectrum is accurate below 2 MeV, the Al rate is consistent with a total rate of 1.10(6) neutrons per muon capture. The spectrum is also unfolded for muon capture on O showing a resonance, but the results are inconsistent between the two detectors.

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Keywords

Muons, Neutrons, AlCap

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