Precision Measurement of Parity Non-Conserving, Weak-force Induced Transitions in Atomic Cesium

我们通过四种基本力来理解我们生活的宇宙：引力、电磁力、弱力（负责放射性和衰变）和强力（提供将原子核结合在一起的力）。将这三种力（电磁力、弱磁力和强磁力）统一起来的理论框架被称为标准模型，它在解释一系列可观察到的现象和预测其他现象方面非常成功。然而，有几个值得注意的效应是标准模型无法解释的，包括宇宙中规则物质的优势（但反物质很少），以及暗物质和暗能量的存在和本质。对星系旋转的观测提供了暗物质存在的证据。由此，我们知道宇宙中包含的物质比我们所能观测到的要多得多。但我们对这种“暗物质”是什么知之甚少，也不知道除了通过引力之外，它是如何与我们可以观察到的物质相互作用的。在这个项目中，首席研究员和他的团队将使用激光场与铯原子的极弱光学相互作用的精确测量来测试标准模型，并寻找标准模型范围之外的物理效应的特征。首席研究员和他的研究小组正在开发两种测量技术来探测铯原子中的弱力相互作用。每种测量技术都是双色相干控制的一种变体，其中光学或射频范围内的两个跃迁幅度相互干扰。一次测量，基于6s 2S1/2 &amp；#8594；7s 2S1/2跃迁，旨在提供铯核弱电荷的改进值。第二种，基于基态超精细组分之间的9.19 GHz跃迁，仅仅是由于核自旋相关的贡献，如核的拟极点矩。当然，维曼在1997年的研究中选择了铯原子，该小组的测量结果仍然是所有原子物种中对弱电荷最精确的测量。铯也是唯一被观测到核顺极矩的物质。弱电荷的测量与标准模型预测的一致程度将对标准模型之外的各种物理模型施加约束。相干控制技术有望降低测量对系统误差的敏感性，这对这些测量的成功至关重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

We understand the universe in which we live through four fundamental forces: gravitational, electromagnetic, weak (responsible for radioactivity and beta decay), and strong (which provides the force that binds atomic nuclei together). A theoretical framework that unifies three of these forces (electromagnetic, weak and strong) is known as the standard model, and has been very successful at explaining a broad range of observables and predicting others. There are, however, several notable effects that the standard model has not been able to explain, including the preponderance of regular matter in the universe (but very little anti-matter), and the existence and nature of dark matter and dark energy. The evidence of the existence of dark matter is provided by observations of the rotation of galaxies. From this, we know that the universe contains much more matter than we have been able to observe. But we know very little about what this "dark" matter is, or how, other than through gravity, it interacts with the matter that we can observe. In this project, the principal investigator and his team will use precision measurements of extremely weak optical interactions of a laser field with cesium atoms to test the standard model, and to search for signatures of physical effects that lie outside the realm of the standard model. The Principal Investigator and his research team are developing two measurement techniques to probe the weak force interactions in atomic cesium. Each measurement technique is a variant of two-color coherent control, in which the amplitudes for two transitions in the optical or radio-frequency range interfere with one another. One measurement, based on the 6s 2S1/2 → 7s 2S1/2 transition, is designed to provide an improved value of the weak charge of the cesium nucleus. The second, based on the 9.19 GHz transition between the hyperfine components of the ground state, is due solely to nuclear-spin dependent contributions such as the anapole moment of the nucleus. Atomic cesium was, of course, the choice of Wieman for his 1997 work, and that group's measurement is still the most precise measurement of the weak charge in any atomic species. Cesium is also the only species in which the nuclear anapole moment has been observed. The degree to which the measurement of the weak charge agrees with the standard model prediction will place constraints upon various models of physics beyond the standard model. The coherent control technique is expected to result in a reduction of the susceptibility of the measurement to systematic errors, critical for the success of these measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.