Model-independent determination of hadronic neutral-current couplings

Completion of a second generation of experiments on neutrino-induced neutral-current reactions allows a more discriminating study of neutral-current couplings to hadrons. To minimize the sensitivity to model-dependent analyses of inclusive and exclusive pion data, we base our work on measurements of deep-inelastic and elastic reactions alone. Within the regions allowed by the deep-inelastic data for scattering on isoscalar targets, the coupling constants are fit to the q² dependence of the neutrino-proton elastic scattering data. This procedure initially yields two solutions for the couplings. One of these, at θL=55^∘ and θR=205^∘, is predominantly isoscalar and therefore is ruled out by only qualitative consideration of exclusive pion data. The other solution at θL=140^∘ and θR=330^∘, is thus a unique determination of the hadronic neutral-current couplings. It coincides with solution A obtained in earlier work, and is insensitive to variations of MA within 2 standard deviations of the world average. When constrained to the coupling constants required by the Weinberg-Salam model, the fit agrees with the data to within 1 standard deviation.