Measurement of Parity Nonconservation in Ytterbium

镱的宇称不守恒（PNC）研究的动机是利用现代桌面激光光谱技术探测原子核内的物理。原子PNC实验是研究基本核和粒子相互作用的独特而强大的工具。这一点的例子是发现了原子核的反极点矩（一种违反宇称的电磁多极），以及测量铯原子中违反宇称的电子-核子相互作用，精确度达到0.35%。在原子镱中，PNC振幅与铯中的PNC振幅相比增强了两个数量级。这有助于测量镱的两个非零核自旋同位素的顶点矩。此外，稳定的镱同位素的宽范围对于测量中子半径沿着同位素链的变化是有吸引力的。该项目旨在测量镱的PNC效应，其精度超过铯的测量精度。该项目的智力价值在于，它可以解决宇称破坏弱核相互作用的理论和测量之间的不一致，并将提供通过其他手段极难获得的补充信息。这些实验也将产生关于同位素链中均方中子半径变化的信息，这除了是核理论的基本测试之外，还确定了富中子核物质的对称能的密度依赖性，这对中子星星结构和重离子碰撞有影响。重要的是，无论是原子核的反极点矩测量还是中子分布测量都不依赖于高精度的理论，尽管原子计算的精确度要优于15%才能提取出原子核的反极点。除了原子、核和粒子物理学之外，镱PNC实验的更广泛影响还扩展到各种不同的领域。为PNC实验开发的理论和实验工具对使用镱研究量子简并气体和新型光学频率标准的项目具有重要意义。利用超冷镱原子寻找原子核电偶极矩的新实验将受益于这项工作中获得的信息。加州大学伯克利分校与欧洲，俄罗斯，澳大利亚和印度的一些大学建立了广泛的国际合作，这将有助于该领域的新进展，并交流新的想法和开发新的实验技术。与正在进行的工作一样，一些研究生和本科生将继续在研究和合作中发挥关键作用。

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.