Fundamental symmetry tests with the francium laser trap facility at ISAC

使用 ISAC 的钫激光陷阱设施进行基本对称性测试

• 批准号: SAPPJ-2022-00035
• 负责人: Gwinner, Gerald
• 金额: $ 14.34万
• 依托单位: University of Manitoba
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=762985
• 关键词: Fundamental; symmetry; tests; francium; laser

The fundamental forces of nature are one of the fascinating subjects that can be studied at the ISAC radioactive beam facility at TRIUMF, Canada's national particle accelerator laboratory. 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 the possibility to study atomic parity- violation in francium (Fr), an element combining a very heavy nucleus (Z=87) with the simple, essentially hydrogen-like, 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 are slowed down with laser light and captured into a `magneto--optical' laser trap, suspended in free space as a millimeter-sized cloud of up to one millions atoms, at temperatures millions of times colder than room temperature. This permits manipulation of individual atoms with unheard-of precision. To harness these capabilities, we have established the francium trapping facility at ISAC and are now using this francium source to carry out a program of precision experiments using laser and microwave spectroscopy. Previously, amongst other work, we have investigated the distribution of magnetism inside the nuclei in a chain of francium isotopes. Recently we started to excite francium's outer valence electron from its ground state, the 7s orbital, to the 8s state. In the absence of applied external electric fields, this highly forbidden transition is roughly 13 orders of magnitude harder to excite than a typical atomic transition. We now succeeded in observing this process for the first time, by amplifying the available laser light 4000-fold in what is known as a power buildup cavity, where the light bounces between two mirrors whose distance must be kept constant to less than the size of an atom. This device has to reside inside our ultra-high vacuum chamber mounted on a beamline at ISAC, which proved very challenging. This work provides the basis for measuring the signature of the weak interaction: The likelihood to excite 8s is slightly different when observing the mirrored process. By putting the atoms in orthogonal electric and magnetic fields, we can create the mirror flip by reversing either one of the two fields' direction, while keeping the other the same. In the coming years, we will work towards preparing the francium atomic parity violation experiment. Supported by NSERC, NRC/TRIUMF, the University of Manitoba, and the University of Maryland.

自然力是可以在加拿大国家粒子加速器实验室TRIUMF的ISAC辐射束设施中研究的迷人课题之一。特别是，导致原子核β衰变的弱力，在呈现宇称破坏现象方面是独一无二的：在自然界中，没有观察到由弱力中介的物理过程的镜像。ISAC提供了研究Fr中原子宇称破坏的可能性，Fr是一种将非常重的原子核(Z=87)与简单的、基本上类似氢的碱的价态结构结合在一起的元素。在元素周期表的前103种元素中，FR核是最不稳定的，寿命最长的同位素只在23分钟内衰变。为了最大限度地利用微小样品，用激光减慢Fr原子的速度，并将其捕获到“磁光”激光陷阱中，悬浮在自由空间中，形成毫米大小的云，最多有100万个原子，温度比室温低数百万倍。这使得对单个原子的操纵具有前所未有的精确度。为了利用这些能力，我们已经在ISAC建立了法郎捕集设施，现在正在使用该法郎源进行一项使用激光和微波光谱学的精密实验计划。在此之前，除了其他工作外，我们还研究了原子核内的磁性在一系列法郎同位素中的分布。最近，我们开始从7S轨道的基态激发到8S态的价电子。在没有外加电场的情况下，这种高度禁忌的跃迁比典型的原子跃迁要难激发大约13个数量级。现在，我们首次成功地观察到了这一过程，通过将可用的激光放大4000倍，在一个被称为能量积累腔的地方，光在两个反射镜之间反弹，两个反射镜的距离必须保持恒定，以小于一个原子的大小。这个装置必须安装在我们安装在ISAC光束线上的超高真空室内，这被证明是非常具有挑战性的。这项工作为测量弱相互作用的特征提供了基础：当观察镜像过程时，激发8S的可能性略有不同。通过将原子置于正交的电场和磁场中，我们可以通过颠倒两个场中的任何一个方向，同时保持另一个相同，来创建镜像翻转。在接下来的几年里，我们将致力于准备法郎原子的宇称破坏实验。由NSERC、NRC/TRIUMF、马尼托巴大学和马里兰大学支持。