Measurement of Parity Nonconservation in Ytterbium

Yb中宇称非守恒(PNC)的研究是由使用现代台式激光光谱学技术探测原子核内的物理的机会推动的。原子PNC实验是研究基本核与粒子相互作用的一种独特而有力的工具。核极矩(一种违反宇称的电磁多极)的发现和对铯中违反电子-核子相互作用的宇称的测量达到了0.35%的准确度，就是例证。在原子Yb中，PNC幅度比在铯中增加了两个数量级。这有助于测量Yb的两个非零核自旋同位素的极极矩。此外，稳定的Yb同位素的大范围对于测量中子半径沿同位素链的变化是有吸引力的。这个项目的目的是测量Yb中的PNC效应，其精确度超过对Ce的测量。该项目的智力优点是，它可以解决违反弱核相互作用的宇称理论和测量之间的不一致，并将提供通过其他手段极其困难地获得的补充信息。这些实验还将提供关于同位素链中均方中子半径变化的信息，这除了是对核理论的基本检验外，还确定了富含中子的核物质对称能量的密度依赖关系，这对中子星结构和重离子碰撞有影响。重要的是，无论是极点矩测量还是中子分布测量都不依赖于高精度的理论，尽管提取核极点需要原子计算精度达到15%以上。除了原子、核物理和粒子物理之外，Yb PNC实验的更广泛影响延伸到各种不同的领域。为PNC实验开发的理论和实验工具对利用Yb研究量子简并气体和新型光学频率标准具有重要意义。使用超冷Yb原子来搜索核电偶极矩的新实验将从这项工作中获得的信息中受益。加州大学伯克利分校小组与欧洲、俄罗斯、澳大利亚和印度的一些大学在该项目中建立的广泛国际合作将有助于该领域的新进展，并有助于交流新思想和开发新的实验技术。正如正在进行的工作一样，几名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.