Our project - Fundamental Studies in Nuclear Physics - at California Institute of Technology is primarily focused on experimental research addressing fundamental properties of the free neutron. In particular we will continue taking data with the UCNA experiment while also developing hardware for construction of a new, highly sensitive experiment to search for the neutron's electric dipole moment.
The UCNA experiment has already produced a 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 CKM 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 we are 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 electric dipole moment experiment - nEDM at the Spallation Neutron Source at Oak Ridge National Laboratory - is to improve the sensitivity by a factor of 100 compared to previous measurements; observation of an electric dipole moment 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 and the new physical phenomena that is responsible.
Non-technical Description of Project
Our project at Caltech is primarily focused on studying fundamental properties of the free neutron. The neutron is an unstable particle and decays with a ten minute half-life into a proton, an electron and an anti-neutrino. We are making precision measurements of the neutron decay using very slow neutrons that can be stored in bottles. These measurements should allow us to make the most precise measurements of the distribution of electrons from the decay of spin-polarized neutrons. These data can push our understanding of the neutron's decay to the limits of theoretical understanding and may indicate that our current picture is incomplete and must be revised.
We are also developing a new experiment to search for an electric dipole for the free neutron. An electric dipole is a separation of the plus and minus charge within this neutral particle. The existence of this dipole would signal a significant breakdown of so-called Charge-Parity (CP) symmetry. A significant breakdown of this symmetry has been suggested to explain why the universe is dominated by material composed of standard particles with virtually no anti-particles present in the universe. This puzzle (more matter than anti-matter) has stumped physicists for many years and we hope to discover and measure the neutron's electric dipole to help explain this basic property of the universe.
We also note that participation by postdoctoral scholars as well as graduate and undergraduate students 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.
