Investigations toward atomic parity-nonconservation and anapole measurements in francium

自然界的基本力量是可以在ISAC研究的迷人课题之一，ISAC是加拿大TRIUMF新的世界级放射性束设施。特别是，导致原子核β衰变的弱力在显示宇称破坏现象方面是独一无二的：由弱力介导的物理过程的镜像在自然界中是观察不到的。ISAC提供了一个独特的可能性，研究原子宇称违反在<$（Fr），一个元素结合了一个非常重的核（Z=87）与简单的，基本上是氢，价结构的碱金属。在元素周期表的前103种元素中，Fr核是最不稳定的，寿命最长的同位素衰变仅需23分钟。为了最大限度地利用微小的样品，Fr原子将被激光减速，并被捕获到一个“磁光”激光陷阱中，悬浮在自由空间中，温度比室温低数百万倍。精确的激光光谱学将使我们能够观察宇称违反的影响。最终的目标是在粒子物理学的标准模型（迄今为止非常成功）之外寻找“新”物理学。该实验的巨大技术挑战是实施稳健且极其有效的原子操作和信号检测方法，以最佳利用微小的Fr样品。在马尼托巴大学进行的稳定铷原子的先驱实验将开发所需的技术，并寻找“负能态”的影响，即虚拟电子-正电子对的产生，对宇称违反测量中使用的原子跃迁的影响。

The fundamental forces of nature are one of the fascinating subjects that can be studied at ISAC, Canada's new world-class radioactive beam facility at TRIUMF. In particular, the weak force, causing the beta-decay of nuclei, is unique in exhibiting the phenomenon of parity-violation: the mirror images of physical processes mediated by the weak force are not observed in nature. ISAC offers a unique possibility to study atomic parity-violation in francium (Fr), an element combining a very heavy nucleus (Z=87) with the simple, essentially hydrogenlike, valence structure of an alkali. Fr nuclei are the least stable among the first 103 elements in the periodic table, the longest-lived isotope decays in only 23 minutes. To make optimum use of the minute sample, the Fr atoms will be slowed down with laser light and captured into a `magneto-optical' laser trap, suspended in free space at temperatures millions of times colder than room temperature. Precise laser spectroscopy will allow us to observe the effects of parity-violation. The ultimate goal will be to search for `new' physics outside the - so far very successful - Standard Model of particle physics. The great technical challenge of this experiment is to implement robust and extremely efficient atom-manipulation and signal-detection methods to make optimum use of the minute Fr sample. A precursor experiment with stable rubidium atoms at the University of Manitoba will develop the required techniques and look for the effects of 'negative-energy states', i.e. the creation of virtual electron-positron pairs, on the atomic transition used in the parity-violation measurement.