High precision cold neutron beta decay correlation measurements at the SNS; the Nab experiment.

亚原子物理学界目前研究工作的一个主要重点是验证和寻找所谓的粒子物理标准模型的可能扩展，该模型旨在预测和描述物质的基本组成部分及其相互作用。我们目前对所有物理现象的理解都基于四种基本相互作用：引力、电磁相互作用、强相互作用和弱相互作用。弱相互作用在四种已知力中扮演着特殊的角色，因为它是唯一一种已知违反宇称的力。一般来说，宇称是自然界中一种基本的对称性，将过程及其镜像联系起来。这里提出的工作涉及使用亚原子粒子之间的弱相互作用作为其基本性质的探针的研究。该实验使用高强度中子源和粒子加速器，要么搜索非常小的空间，并产生不对称的产物之间的反应的弹丸和一个给定的目标，或以高精度测量粒子（即中子）衰变产物的属性。事实上，只有弱相互作用违反宇称，其短范围，使这些测量非常有用的探针非常小的影响核子内。目前公认的数学和现象学描述我们的知识，关于亚原子粒子之间的相互作用被称为标准模型。虽然标准模型非常成功，但有很强的理论理由，例如大量的可调参数，可以预期标准模型是一个低能有效的理论，对自然界进行了一些更基本的描述。拟议的项目将包括使用冷中子进行测量，在田纳西州橡树岭的斯普林中子源进行。这个世界领先的新设施将使我们能够执行一个超精确测量中子弱相互作用的计划。

A major focus of the current research effort within the subatomic physics community is the verification of and search for possible extensions to the so called Standard Model of particle physics, which seeks to predict and describe the fundamental building blocks of matter and their interactions. Our current understanding of all physical phenomena is based on four fundamental interactions: gravitation, the electromagnetic interaction, the strong interaction, and the weak interaction. The weak interaction takes a special role among the four known forces, as it is the only one known to violate parity. Generally, parity is a fundamental symmetry in nature, relating processes and their mirror images. The work proposed here involves studies which use the weak interaction between subatomic particles as a probe for their fundamental properties. The experiments use high intensity neutron sources and particle accelerators to either search for very small spatial and yield asymmetries in the products of the reaction between the projectile and a given target, or to measure with high accuracy the properties of particle (i.e. neutron) decay products. The fact that only the weak interaction violates parity, and its short range, makes these measurements highly useful probes of very small effects inside nucleons. The currently accepted mathematical and phenomenological description of our knowledge about the interactions between subatomic particles is known as the Standard Model. Although highly successful, there are strong theoretical reasons, such as the large number of adjustable parameters, to expect that the Standard Model is a low energy effective theory of some more fundamental description of nature. The proposed project will consist of measurements using cold neutrons, conducted at the Spallation Neutron Source in Oak Ridge, Tennessee. This world-leading new facility will permit us to carry out a program of ultra-precise measurements of weak interactions of the neutron.**