Our celebration of Krystyna Lopez's successful doctoral dissertation defense, with her supervisor, Mike Snow.
Dissertation Title: Probing Exotic Interactions Using Slow Neutron Polarimetry
Abstract: Precision neutron spin rotation measurements act as a powerful probe of physics within and beyond the Standard Model. Slow neutron polarimetry techniques are uniquely sensitive for studying weakly coupled interactions at mesoscopic length scales, where new interactions may arise via light boson exchange. Three types of spin-dependent interactions are explored: the first is a parity-violating neutron–nucleon interaction arising from the hadronic weak interaction in the SM; the second and third are a velocity-dependent neutron–matter interaction and neutron spin–electron spin interaction that would signal exotic fifth forces. This work focuses on the development and validation of experimental systems that significantly improve the precision of neutron spin rotation measurements in search of these interactions. Improvements were made to a novel, non-magnetic liquid helium target and pumping system; in parallel, a highly sensitive magnetic field mapping system was developed, programmed, and tested to characterize target materials at the picotesla scale. Additionally, experimental systems were developed, and neutron spin rotation measurements were performed using ferrimagnetic terbium iron garnet at Oak Ridge National Lab, producing the first polarized neutron images of the internal magnetization of a ferrimagnet crossing its compensation temperature and placing the most stringent bounds on the neutron-electron g_A g_A exotic coupling constant at intermediate interaction length scales.