CAREER: Investigation of Spin Evolution in Magnetic Ultracold Neutron Bottles Used to Measure the Free Neutron Lifetime

Tennessee Technological University, Cookeville TN

Investigators

Abstract

An isolated neutron lives for about fifteen minutes before disintegrating into three lighter particles. This fundamental process plays a significant role in cosmology, and its study complements current efforts to discover new physics. Two laboratory techniques exist to determine the lifetime of a neutron with high precision, but they disagree significantly in their reported values. This discrepancy must be addressed in order to realize the potential of these techniques to help probe new physics. The research conducted with this award directly supports that effort by examining the behavior of very low energy (or "ultracold") neutrons which are magnetically confined in order to determine the neutron lifetime. The research involves a broad set of ideas and skills appropriate for undergraduate involvement and will be used to form the kernel for an interdisciplinary undergraduate research training, mentoring, and outreach program at Tennessee Technological University. Research activities will be carried out in conjunction with the UCNtau collaboration, which has constructed a magneto-gravitational ultracold neutron trap with a long intrinsic neutron storage time and demonstrated a detection strategy capable of making multiple high-precision measurements in a single accelerator cycle at the Los Alamos National Laboratory ultracold neutron source. Losses due to spin evolution in this trap will be empirically characterized by developing a high-fidelity spin-tracking Monte Carlo simulation of the experiment which, when combined with measurements of the mean trap lifetime as a function of the polarization-preserving ambient magnetic field magnitude, will be used to characterize indirectly the loss rate associated with spin evolution in the trap, sufficient for completing measurement of the neutron lifetime to an accuracy of one second. Measurements in a dedicated test cell will provide information necessary to assess directly the effect of spin evolution in a very high-precision (well below 0.1%) magnetic trap measurement of the free neutron lifetime.