Fundamental Studies in Nuclear Physics

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Precise experimental tests of fundamental particle properties are now a well-established way to search for new laws of nature beyond our current physical knowledge. This research program centers around two experiments to make precise measurements of physical properties of the neutron. The first experiment, called UCNA, is being carried out at the Los Alamos National Laboratory, using extremely slow neutrons (ultra-cold neutrons, or UCN), which have such low energy that they can be stored in magnetic "bottles". This allows the experiment to make a precise measurement of the direction of the electron emitted when a neutron decays into a proton, an electron and a particle called an anti-neutrino. This provides needed information about the theory of radioactivity (also called the weak nuclear force). In addition, the PI and his group are developing equipment for a future experiment to search for a possible electric dipole moment (EDM) of the neutron. The existence of this EDM would be a signal of new physics beyond our current knowledge and could help to explain why the universe is dominated by matter, whereas the Standard Model of particle physics predicts there should be nearly equal amounts of matter and antimatter. Participation by postdoctoral scholars, graduate students, and undergraduates is an essential part of the research program, affording young researchers exceptional opportunities to advance their training and education in this frontier area of nuclear physics. This project is primarily focused on experimental research addressing fundamental properties of the free neutron. In particular the group will continue analyzing data from the UCNA experiment while also constructing hardware for a new, highly sensitive experiment to search for the neutron's EDM. The UCNA experiment will provide a high precision measurement of the beta-asymmetry in neutron decay using Ultra-Cold Neutrons for the first time. This quantity allows a sensitive test of the unitarity of the weak quark-mixing matrix and has the potential to provide evidence for new physics beyond the Standard Model of particle interactions. With recent improvements to the apparatus the group is poised to improve the precision on the asymmetry down to ~ 0.3% with additional data-taking and analysis during the period of this grant. The goal of the new EDM experiment, called nEDM, is being done at the Spallation Neutron Source at Oak Ridge National Laboratory and will improve the upper limit by a factor of 100 compared to previous measurements; observation of an EDM signals violation of time-reversal and charge-parity (CP) symmetry, and could provide important information related to the origin of the matter-antimatter asymmetry of the universe.