High Precision Measurements of Beta Decay Using Stored Ultracold Neutrons and Cold Neutron Beams
Albert R. Young
Paul R. Huffman
Daniel D Stancil
Project runs from 07/15/2019 to 06/30/2022
This proposal covers measurements of neutron beta decay using a cold neutron beam at the Spallation Neutron Source and ultracold neutron (UCN) experiments at the Los Alamos National laboratory. The goal of these experiments are measurements which reduce the reduce the current uncertainties in the neutron lifetime to the level of about 1 second (the lifetime is 880 seconds in the latest average of the global data set) and the uncertainty in the axial coupling constant to about 0.025%. These quantities are important for high precision predictions of the energy output of the sun, the cross-sections for neutrinos coming from reactors and searches for physics beyond the standard model of particle physics.
Each experiment has unique strengths, in that Nab uses a cold neutron beam to provide an intense, localized source of neutrons, ideal for a time-of-flight spectrometer. The other two experiments, UCNA and UCNtau, use UCNs (neutrons going so slowly they can be stored in material vessels and magnetic traps) to help overcome systematic errors. The UCN measurements are stationed at the LANL UCN source, a solid deuterium source developed through earlier efforts co-led by our NCSU group.