A determination of the neutral current coupling constants from inclusive and semi-inclusive neutrino data

Abstract

Measurements of the π + π − ratio in the semi-inclusive neutral current reactions v( v) + N → v( v) + π + … have been announced from an analysis of the Gargamelle experiment. These data, when interpreted with the help of the quark-fragmentation model, allow a determination of the fundamental parameters of the neutral hadron current. Writing the interactions as L= G 2 ψ Vϵ α(1+ϵ 5)ψ V[ ψ Uϵ α u L (1+ϵ 5)+u R (1−ϵ 5) ψ u+ ψ dϵ α d L (1+ϵ 5)+d R (1−ϵ 5) ψ d ] we find u L 2 = 0.082 ± 0.035, u R 2 = 0.055 ± 0.025, d L 2 = 0.158 ± 0.035, d R 2 = 0.001 ± 0.025. These numbers are in accord with the Weinberg-Salam model for sin 2 θ ≈ 0.3 and should provide severe constraints for all models of the neutral current.