The Physics of Ultracold Neutrons and Fierz Interference in Beta Decay

Citation

Hickerson, Kevin Peter (2013) The Physics of Ultracold Neutrons and Fierz Interference in Beta Decay. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/K8CK-MQ14. https://resolver.caltech.edu/CaltechTHESIS:11022012-135115177

Abstract

type of reflector that directs UCN upward in to vertical paths. Next we examine UCN passing through thin, multilayered foils. In the remaining sections we investigate the so-called Fierz interference term of free neutron beta decay, denoted b_n. It is theorized that contributions to scalar and tensor interactions from physics beyond the Standard Model could be detectable in the spectrum of neutron beta decay, manifest as a nonzero value for b_n. We investigate three techniques for measuring b_n. The first is to use the primordial helium abundance fraction and compare that to predictive Big Bang nucleosynthesis calculations. Second we extract b_n from the spectral shape generated by the 2010 data set of the UCNA experiment. Third, we discuss progress toward constructing the UCNb experimental prototype. We present the design of this new experiment that uses the UCN source at LANSCE for measuring b_n, in which UCN are guided into a shielded 4π calorimeter where they are stored and decay. From Big Bang nucleosynthesis we can place the limit 0.021 < b_n < 0.277 (90\% C.L.) on the neutron Fierz term and from the UCNA 2010 data we set -0.044 < b_n < 0.218 (90\% C.L.).

Thesis Files