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

物理宇宙的四种基本力是引力、电磁力、弱力（负责粒子的放射性衰变）和强力（将原子核结合在一起的结合力）。多年来，人们对这些力有了大量的了解，一个统一并总结了我们对这三种力（电磁力、弱磁力和强磁力）的理解的理论模型，被称为标准模型，在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得到解释，或者超出了标准模型预期有效的能量范围（例如宇宙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），但它不会通过我们能够探测到的任何方式与宇宙中的常规物质相互作用。另一个是可能存在的粒子太大了，以至于它们还没有在大型高能粒子加速器（如瑞士的大型强子对撞机）上产生或观察到。然而，在标准模型之外寻找物理学的第三个领域是寻找所提出的扩展对原子中微弱光学跃迁的极其精确测量的间接影响。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弱力诱导的跃迁幅度进行新的、更高精度的测量。上世纪90年代，卡尔·维曼（Carl Wieman）小组在博尔德（Boulder）对这个原子进行了重点测量，这些宇称违反幅度的测量仍然是所有元素中最精确的测量。然而，有必要以更高的精度进行原子宇称违背测量。这样的测量将允许更精确地确定原子核的弱电荷，并由此改进了低动量传递时电弱混合角的确定。这种混合角的能量依赖（或所谓的“运行”）是通过对不同能量的散射测量来测量的，这对扩展标准模型的理论中推测的大质量玻色子提出了重要的限制。这些测量也指导了对暗物质候选者的搜索。原子宇称违反测量也可以用来确定原子核的拟极点矩。这个力矩是由核内的弱相互作用产生的，它对违反宇称振幅的核自旋依赖提供了主要贡献。迄今为止，博尔德小组对铯的准极点矩的测量是唯一成功的测量任何元素。由于这个结果大约是预期的两倍大，而且它的大小仍然不清楚，因此需要一个新的测量来验证或反驳它的大小。目前项目的目标是回到铯，进行一套新的高精度测量，以实现这些目标。首席研究员将对这些测量应用双通道相干控制技术。一组测量集中在6s - 7s跃迁上，Wieman之前访问过，而第二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.