Fundamental Symmetry Tests Using Low Energy Neutrons

Intellectual Merit This proposal seeks to aaswer the following questions through study of the interactions of low-energy neutrons: a) What descriptions of particle physics beyond the standard model are possible? b) Why is our universe made up of matter and not anti-matter? c) What role does the weak interaction play in the binding of nuclei? and d) What is the structure of the proton and neutron? The first two questions are being addressed through involvement in an experiment to measure the neutron electric dipole momoment (nEDM). This experiment seeks to observe a nEDM larger than can be accounted for by the standard model. This would resolve the CP-symmetry violation necessary to explain the baryon asymmetry of the universe. In this experiment, polarized ultracold neutrons are stored in a superfluid helium cell to measure their precession frequency about a magnetic field. The deviation of this frequency in the presence of a strong electric field is used to extract the electric dipole moment of the neutron. The sensitivity of this experiment is statistics limited by the rate at which neutrons can be generated, polarized, and captured in the bottle. Conventional polarizers absorb over half of the neutrons, transmitting only the desired spin state. The proposed research will significantly increase the flux of polarized neutrons to this experiment by sorting the neutrons by spin state into the two measurement cells. The last two questions are being addressed through measurements of the hadronic weak interaction (HWI). Although this component of the nuclear force is seven orders of magnitude smaller than its strong counterpart, it can be isolated through its unique property of parity violation (PV). PV has been observed in medium and compound nuclei where effects are magnified by the nuclear structure. However, this same structure complicates the extraction of the underlying HWI, making the results difficult to interpret. The UK group is participating in a series of measurements of PV in few-body systems to systematically characterize the HWI. NPDGamma, the first experiment to run at the SNS Fundamental Neutron Physics Beamline (FnPB), will extract the long-range component of the HWI by measuring the PV correlation a~ . k1 in the reaction: n + p -~ d + ~. Work is underway to gain approval of another experiment, NDTGamma, which uses a deuterium target instead of protons. A third experiment, n3He, has been approved to run at the SNS FnPB to measure a~ k~ in the reaction: n + 3He -~ p + t. This proposal will support participation in these three experiments and in development of a 311e target/wire chamber. Broader Impact These projects will have significant effect on undergraduates, graduates, and postdocs at the Uni- versity of Kentucky, especially women, minorities, and students from the Appalachian region. These students have the opportunity of participating in cutting-edge research at Los Alamos National Lab- oratory (LANL) and Oak Ridge National Laboratory (ORNL). Research on the nEDM prompted an upcoming tour for the Society of Physics Students to a local company working with electromag- netic pulses. The P1 is incorporating portions of this work into his course on modern physics, and has developed an introduction to programming in C, C++, and ROOT. The work on the two FnPB beamlines will benefit all subsequent experiments. General-purpose software libraries developed for this research will be made publicly available.