Fundamental physics with cold and ultra-cold neutrons

在已知存在于自然界的四种基本力——引力、电磁力、强核力和弱核力中，只有弱相互作用违反宇称。当宇称被破坏时，实验的结果与作为其镜像的实验的结果不同。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。我们测量的不对称类型只能出现在弱相互作用作为反应的一部分的结果中。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。一个由马尼托巴大学、温尼伯大学、北不列颠哥伦比亚省大学和加拿大核与粒子物理实验室组成的加拿大研究小组，启动了一个加拿大的中子物理基础实验项目，以研究标准模型的性质和可能的扩展。该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，以及使用超冷中子的测量，将在TRIUMF和新墨西哥州的洛斯阿拉莫斯国家实验室进行。这些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计划。

Among the four fundamental forces that are known to exist in nature, gravity, electromagnetism, and the strong and weak nuclear forces, only the weak interaction violates parity. When parity is violated, the results of an experiment differ from those obtained with an experiment that was set up as its mirror image. 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 type of asymmetries we measure can only emerge as a result of the weak interaction being part of that reaction. 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. A Canadian research group, consisting of the universities of Manitoba, Winnipeg, Northern British Columbia, and TRIUMF, Canada's laboratory for nuclear and particle physics, has initiated a Canadian program in fundamental neutron physics experiments to investigate the properties and possible extensions of the Standard Model. The 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.