Fundamental physics with cold neutrons at the Spallation Neutron Source

目前亚原子物理界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，该模型寻求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。弱相互作用在已知的四种力中扮演着特殊的角色，因为它是唯一已知的违反平等性的力。一般来说，宇称是自然界中的一种基本对称性，它将过程及其镜像联系在一起。这里提出的工作包括使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。这些实验使用高强度中子源和粒子加速器来寻找弹丸与给定目标之间反应产物中非常小的空间和产额不对称性，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了宇称，而且范围很短，这使得这些测量非常有用，因为核子内部的影响非常小。目前公认的关于亚原子粒子之间相互作用的知识的数学和现象学描述称为标准模型。虽然非常成功，但也有很强的理论理由，如大量的可调参数，期待标准模型是一个低能有效的理论，对一些更根本的性质进行描述。拟议的计划将包括在田纳西州橡树岭的散裂中子源进行的使用冷中子的测量，以及将在新墨西哥州的TRIUMF和洛斯阿拉莫斯国家实验室进行的使用超冷中子的测量。这些世界领先的新设施将使我们能够对中子的弱相互作用进行超精密测量。

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 program will consist of measurements using cold neutrons, conducted at the Spallation Neutron Source in Oak Ridge, Tennessee and of measurements using ultracold neutrons, to be conducted at TRIUMF and Los Alamos National Laboratory, New Mexico. These world-leading new facilities will permit us to carry out a program of ultra-precise measurements of weak interactions of the neutron.