Measurement of Parity Nonconservation in Ytterbium

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

The study of parity nonconservation (PNC) in ytterbium is motivated by the opportunity to probe physics within the atomic nucleus using modern table-top laser-spectroscopy techniques. Atomic PNC experiments are a unique and powerful tool for the study of fundamental nuclear and particle interactions. This is exemplified by the discovery of the nuclear anapole moment (an electromagnetic multipole that violates parity) and the measurement of the parity violating electron-nucleon interaction in cesium to 0.35% accuracy. In atomic ytterbium, the PNC amplitude is enhanced by two orders of magnitude compared to that in cesium. This facilitates measurements of the anapole moments of two nonzero-nuclear-spin isotopes of ytterbium. Furthermore, the broad range of stable ytterbium isotopes is attractive for measuring the variation of neutron radii along an isotopic chain. This project aims at measuring PNC effect in ytterbium to an accuracy exceeding that obtained for cesium. The intellectual merit of this project is that it may resolve inconsistencies between the theory and measurements of the parity violating weak nuclear interactions and will provide complementary information that is exceedingly difficult to access by other means. These experiments will also yield information on variation of the mean-square neutron radii in a chain of isotopes, which in addition to being a fundamental test of nuclear theory, pins down the density dependence of the symmetry energy of neutron-rich nuclear matter which has impacts on neutron star structure and heavy ion collisions. Importantly, neither the anapole-moment measurement nor the neutron-distribution measurement relies on high-precision theory, although atomic calculations accurate to better than 15% are required to extract the nuclear anapole. The broader impact of an ytterbium PNC experiment extends to a variety of different fields besides atomic, nuclear and particle physics. The theoretical and experimental tools developed for the PNC experiment have an essential significance for projects employing ytterbium for studies of quantum degenerate gases and novel optical frequency standards. New experiments using ultra-cold ytterbium atoms to search for the nuclear electric dipole moment would benefit from the information obtained in this work. A broad international collaboration within this project established between the UC Berkeley group and a number of universities in Europe, Russia, Australia, and India will contribute to new advances in this field and to exchange of new ideas and development of novel experimental techniques. As in the ongoing work, several graduate and undergraduate students will continue to play key roles in the research and collaborations.