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

目前亚原子物理学界的一个主要研究重点是验证和寻找所谓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是基于四种基本的相互作用：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的力中扮演着特殊的角色，因为它是已知的唯一违反宇称的力。一般来说，宇称是自然界中一种基本的对称性，将过程和它们的镜像联系起来。这里提出的工作包括利用亚原子粒子之间的弱相互作用作为探测其基本性质的研究。实验使用高强度中子源和粒子加速器，在弹丸和给定目标之间的反应产物中寻找非常小的空间和产量不对称，或者高精度地测量粒子（即中子）衰变产物的性质。事实上，只有弱相互作用违反宇称，而且它的范围很短，这使得这些测量成为核子内部非常小的影响的非常有用的探针。目前公认的关于亚原子粒子之间相互作用的数学和现象学描述被称为标准模型。尽管非常成功，但有很强的理论理由，比如大量可调参数，可以预期标准模型是对自然的一些更基本描述的低能量有效理论。拟议的项目将包括使用冷中子的测量，在田纳西州橡树岭的散裂中子源进行。这个世界领先的新设备将使我们能够进行中子弱相互作用的超精确测量项目

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.**