Strength of the antineutrino-proton neutral-current interaction

Using the Fermilab 15-foot hydrogen bubble chamber exposed to a broad-band $\overline{\nu }$ and $\nu$ beam, we have studied the neutral-to-charged-current cross-section ratio $R$ for interactions on protons. The ratio $R^{\overline{\nu }p}$ is found assuming various forms of the neutral-current couplings. The data are consistent with the predictions of the Weinberg-Salam model and, assuming this model, we obtain $R^{\overline{\nu }p}=0.42\mathrm{}\pm 0.13$.