Towards Precision Measurements of Atomic Parity Violation Using Two-Pathway Coherent Control

物理宇宙的四个基本力是引力、电磁、弱(负责粒子的放射性衰变)和强(将原子核结合在一起的结合力)。多年来，关于这些力已经了解了很多，一个统一和总结了我们对其中三种力(电磁、弱和强)的理解的理论模型，被称为标准模型，在它的许多预测中都非常精确。然而，仍然存在一些非常重要的悬而未决的问题，这些问题无法在标准模型中解释，或者属于标准模型预期有效的能量范围之外(例如，在宇宙非常早期阶段存在的条件)。其中之一是暗物质的存在和性质：我们知道宇宙中存在的物质(因为宇宙的缓慢膨胀)，但不会通过我们能够探测到的任何手段与宇宙中的常规物质相互作用。另一种可能性是，可能存在质量如此之大的粒子，以至于大型高能粒子加速器(如瑞士的大型强子对撞机)尚未产生或观测到这些粒子。然而，在标准模型之外寻找物理学的第三个领域是寻找拟议的扩展对原子中微弱光学跃迁的极其精确的测量的间接影响。这是这项研究工作的重点，它可以帮助指导这些关于宇宙的基本问题的答案。首席研究员和他的团队将对铯原子中由弱力诱导的跃迁幅度进行新的、更高精度的测量。这个原子是卡尔·威曼小组在20世纪90年代的S在博尔德进行的先前测量的焦点，这些对宇称破坏幅度的测量仍然是所有元素中报道的最精确的。然而，需要以更高的精度进行原子宇称破坏测量。这样的测量将允许更精确地确定原子核的弱电荷，并由此改进对低动量转移时弱电混和角的确定。通过在不同能量下的散射测量来测量的这种混合角的能量依赖(或被称为“运行”)，对扩展标准模型的理论中的猜想的大质量玻色子施加了重要的约束。这些测量也指导了对暗物质候选者的搜索。原子宇称破坏测量也可以用来确定原子核的极点矩。这一由原子核内弱相互作用产生的力矩，对宇称破坏幅度的核自旋依赖提供了主要贡献。到目前为止，博尔德团队对铯的极点时刻的测量是所有元素中唯一成功的测量。由于这一结果大约是预期的两倍，而且其大小仍不清楚，因此需要一种新的测量方法来验证或驳斥其大小。本项目的目标是返回铯进行一系列新的高精度测量，以实现这些目标。首席研究员将对这些测量应用双路径相干控制技术。其中一组测量以Wieman之前访问过的6S-7S跃迁为中心，而另一组测量将检查超精细组分之间基态跃迁的类似影响。

The four fundamental forces of the physical universe are gravitational, electromagnetic, weak (responsible for radioactive decay of particles), and strong (the binding force that holds the nuclei of atoms together). A great deal about these forces has been learned over the years, and a theoretical model that unifies and summarizes our understanding of three of these forces (electromagnetic, weak, and strong), known as the Standard Model, has been extremely precise in many of its predictions. There still persist, however, several very important open questions that cannot be explained within the Standard Model, or which fall outside the energy range in which the Standard Model is expected to be valid (such as conditions that existed during the very early stages of the universe). One of these is the existence and properties of dark matter: matter within our universe that we know exists (because of the slowing expansion of the universe), but which does not interact with regular matter in the universe through any means that we have been able to detect. Another is the possible existence of particles that are so massive that they have not yet been generated or observed at the large high-energy particle accelerators (such as the Large Hadron Collider in Switzerland). Yet a third area in which to search for physics beyond the Standard Model is to look for the indirect influence of the proposed extensions on extremely precise measurements of weak optical transitions in atoms. This is the focus of this research effort, which can help guide the answers to these fundamental questions about the universe.The principal investigator and his team will carry out new, higher-precision measurements of weak-force-induced transition amplitudes in atomic cesium. This atom was the focus of prior measurements by the group of Carl Wieman in Boulder in the 1990's, and these measurements of the parity violating amplitude are still the most precise reported for any element. There exists, however, a need to carry out atomic parity violation measurements at an even higher precision. Such a measurement will allow a more precise determination of the weak charge of the nucleus, and from that, an improved determination of the electroweak mixing angle at low momentum transfer. The energy dependence (or "running", as it is called) of this mixing angle, as measured through scattering measurements at various energies, places important constraints on conjectured massive bosons in theories that extend the standard model. These measurements also guide searches for dark matter candidates. Atomic parity violation measurements can also be used to determine the anapole moment of the atomic nucleus. This moment, resulting from weak interactions within the nucleus, provides the leading contribution to the nuclear spin dependence of the parity violating amplitude. To date, the Boulder group's measurement of the anapole moment of cesium is the only successful measurement in any element. Since this result is about twice as large as expected, and its magnitude is still not understood, there is a need for a new measurement to either verify or refute its magnitude. The goal of the present project is to return to cesium for a set of new, high-precision measurements that will address these goals. The principal investigator will apply a two-pathway coherent control technique to these measurements. One set of measurements are centered on the 6s - 7s transition, visited previously by Wieman, while a second set will examine similar effects in the ground state transition between hyperfine components.