Fundamental physics with cold and ultra-cold neutrons

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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.