Measurements of sin2θw from studies of the elastic scattering of neutrinos by protons and electrons

This talk is intended to be a brief report on studies of the elastic scattering of neutrinos by protons and electrons. Much of this work has been recently published or is circulating in preprint form. Consequently, a short statement of the motivation and a summary of the experimental method should be sufficient for the purpose here, and attention can be concentrated on the experimental results. The semileptonic and purely leptonic reactions νμp → νμp, bar νμp → bar νμp and νμe → νμe, bar νμe → bar νμe are particularly simple reactions (both experimentally and theoretically) with which to study weak neutral currents. These processes have clean, distinctive experimental signatures, and their interpretation is almost completely constrained with the standard electroweak model. Measurements of the ratio of bar νμ and νμ elastic scattering on protons and the corresponding ratio for elastic scattering on electrons minimize systematic experimental errors and lead directly to values of the fundamental parameter of the electroweak interaction, sin2θw, with minimal ambiguity. Accordingly, the principal motivation in carrying out these studies was the desire to obtain and compare precise values of sin2θw from both the semileptonic and leptonic reactions as still another test of the basic validity of the standard electroweak theory