Measurement of the ratio of neutral to charged current cross sections of neutrino interactions in hydrogen

The ratio R_p of the neutral current to charged current cross sections has been measured in the BEBC bubble chamber filled with hydrogen and exposed to the CERN SPS wideband neutrino beam. It is found that an event selection in terms of the transverse momentum of the hadronic system is very effective in reducing backgrounds and enables R_p to be determined with an error of less than 10%. Combining the results from hydrrogen and isoscalar targets, the individual values of the coupling constants u_L² and d_L² are determined separately to be u_L² = 0.15 +/- 0.06 and d_L² = 0.17 +/- 0.08. The results are compatible with the standard SU (2) × U(1) model. The value of sin²θ_W determined from this experiment is 0.19 +/- 0.04.