Probing Fundamental Physics with Ultracold Neutrons: Following the Bouncing Ball

Dr. Albert R. Young
Department of Physics
North Carolina State University

Ultracold neutrons (UCN) are neutrons with energies below about 400 neV that can be stored in material bottles for hundreds of seconds and poured or guided into a variety of experiments.  The goal of the UCNA experiment is to improve our knowledge of the angular correlation between the emitted electron and the initial spin of the neutron in beta-decay (the beta-asymmetry) using ultracold neutrons.  The precision of this correlation defines the current limits to which fundamental electroweak data can be extracted from neutron decay and also the limits which can be placed on new physics from neutron decay.  In the process of developing their experimental approach, the UCNA collaboration developed the first functioning solid deuterium superthermal source of UCN coupled to a spallation target, initiated a unique program to develop new technology to transport UCN and to understand the systematics of UCN depolarization, initiated the first detailed studies of the backscattering of electrons in the energy range of beta-decay, and developed new technology for low energy proton detection.  The experiment is now fully constructed and is in the process of commissioning.  The motivation and status of this experiment will be reviewed, and recent results of its research and development program presented.