A Method for Proton Detector Efficiency Measurement with Applications in Neutron Beta Decay and Lifetime Experiments
This article proposes a new method to measure the proton detector efficiency for use in "beam" determinations of the free neutron lifetime. There is currently a 4{\sigma} disagreement between the "beam" and "storage" methods of measuring the lifetime of the neutron. A possible reason for this is a systematic uncertainty that is not properly accounted for in one or both types of experiments. Absolute proton counting is an essential facet of the "beam" experimental approach. The absolute detector efficiency is not currently known for existing experiments and could be a source of a hidden systematic error. The proposed absolute calibration techniques can also be extended to new, large area particle detectors designed for future experiments. We propose to laser ionize a beam of atomic hydrogen and simultaneously count both the outgoing protons and electrons. Due to recent advances in UV laser and atomic hydrogen beam technologies, we estimate a count rate as high as ~200k proton-electrons pairs per second under the most favorable scheme discussed. Our proposed technique would remove one of the leading systematic uncertainties in the determination of the neutron lifetime, making an precision of {\pm}0.16 s feasible. Precise and accurate knowledge of the proton detection efficiency is crucial to fully understanding the systematics of the "beam" measurement method as well as developing next generation experiments that will have the precision to test the Standard Model.