Helium 3 ion chambers for precision neutron capture asymmetry measurements

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Our current understanding of the interactions and properties of subatomic particles is described by the so called Standard Model. The model currently combines the electromagnetic interactions, the weak interaction, and the strong interactions into one framework and has enjoyed extensive success in predicting experimental results over the past 50 years. The weak interaction drives the decay of neutrons into protons and lies at the heart of energy generation in a star. The strong interaction acts between subatomic particles called quarks and binds neutrons and protons (nucleons) into nuclei. Despite its success, it is apparent that the Standard Model is only an approximate description of the processes that drive interactions at the subatomic level. Among many reasons supporting this assertion are the fact that the model has many parameters which enter the theory in an ad hoc manner, as well as the glaring omission of gravity from the interactions it describes. The verification of all aspects of the Standard Model and the search for new physics beyond the Standard Model are therefore currently at the leading edge of subatomic particle physics research. A group based at the universities of Manitoba and Winnipeg has initiated a Canadian program in fundamental neutron physics experiments to investigate Standard Model predictions. 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 to search for very small asymmetries in the reaction between the projectile and a given target. Measurements of these asymmetries are highly sensitive probes of very small effects inside nucleons. This proposal requests funding for the construction of helium 3 ion chambers which will be used for precise measurements in neutron capture and decay processes. Since the weak interaction between nucleons is predicted within the Standard Model, but modified in an unknown way by the strong Interaction, the proposed measurements of asymmetries in the neutron capture processes are Standard Model tests in their own right.