A precision measurement of sin2θw from semileptonic neutrino scattering

There is considerable interest in measuring the electroweak mixing parameter sin2θw of the Glashow-Salam-Weinberg theory as precisely as possible: first, its value may be predicted by models of Grand Unification; second, precise measurements of sin2θw from different processes would test the validity of electroweak radiative corrections. Different methods have been used to determine sin2θw over a large range of Q2 values. Figure 1 gives a compilation of sin2θw with remarkable agreement between the results. At present, it is most precisely determined in semileptonic neutrino-nucleon scattering from the ratio of neutral current (NC) to charged current (CC) cross sections, and in proton-antiproton collisions from the W boson mass. Here, results are reported from an experiment of the first type. In order to achieve a higher precision in Rv = NC/CC than in previous experiments, the upgraded CDHS detector was exposed to an optimized version of the CERN narrow-band beam (NBB). This provided a significant increase in statistics and a reduction of the uncertainties related to the neutrino flux. Most of the experiment was performed with neutrinos because the antineutrino NC/CC ratio is less sensitive to sin2θw