Precision experiments in neutron beta decay
Description
A free neutron will disintegrate into a proton after about fourteen and a half minutes, emitting an electron and an antineutrino. The Standard Electroweak Model epitomizes the process with a decay probability distribution function (PDF) derived by Jackson, Trieman, and Wyld. This function depends on the momenta of the daughter particles and the spin of the neutron. Each correlation between these vector quantities is characterized by a correlation coefficient. The work of this dissertation focused on two experiments investigating these coefficients, and thus, the properties of the beta-decay process for polarized neutrons The first of these, called emiT, was an experiment to measure the coefficient (D) that characterizes the triple product between these observables; a product which changes sign under time reversal. The experiment has a four-fold symmetric design to improve statistics over previous measurements of D while mitigating systematics, and has been completed with a result pending. My contribution, in addition to some assembly of the apparatus, consisted of performing an analysis of the data and investigating overall systematics. These systematic issues ultimately precluded the use of the analysis method I employed, however, I was able to give an account of the size of the systematic effects, and other methods have been developed to analyze the data while evading these effects The other experiment, aCORN, will measure the a coefficient, the correlation between the electron and antineutrino momenta. The apparatus for this experiment is now being constructed. The a coefficient is one of the least-precisely known of the correlation coefficients. There have been only three previous attempts to measure it, and all of those experiments relied on the same method, which possesses a systematic limitation in the precision at which a can be measured that is not easy to overcome. aCORN relies on a completely new idea, not limited by the same systematics, which promises to improve this precision significantly. My charge for aCORN was to assemble and test the backscatter-suppressing electron spectrometer to be used, and currently it is the only component which is sufficiently completed and ready for the experimental run