The ratios of neutral-current to charged-current cross sections of v and v interactions, seperately, on proton and neutron targets have been measured. The Big European Bubble Chamber (BEBC), filled with deuterium and equipped with an external muon identifier (EMI) and an internal picket fence (IPF), was exposed to the CERN SPS (anti)neutrino wide-band beam. The measured ratios are R v p= = 0.405 ± 0.024 ± 0.021 , R v n = 0.243 ± 0.013 ± 0.016, R v p = 0.301 ± 0.027 ± 0.024 and R v n = 0.490 ± 0.050 ± 0.037 . (The first error is statistical and the second systematic). From combinations of these ratios the following neutral-current chiral coupling constants have been determined: u L 2 = 0.099 ± 0.018 ± 0.008, d L 2 = 0.202 ± 0.020 ± 0.019, u R 2 = 0.020 ± 0.016 ± 0.009 and d R 2 = 0.002 ± 0.017 ± 0.010. These results agree with the predictions of the SU(2) × U(1) standard electroweak model. Assuming ϱ = 1, the corresponding value of sin 2 θ w is found to be 0.247 ± 0.029, whereas a two-parameter fit to the data yields sin 2 θ w = 0.243 ± 0.046 and ϱ = 0.996 ± 0.041.
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The cross section of the quasi-elastic reactions\(\bar v_\mup \to \mu ^ +\Lambda (\Sigma ^0 )\) in the energy range 5–100 GeV is determined from Fermilab 15′ bubble chamber antineutrino data. TheQ2 analysis of quasi-elastic Λ events yieldsMA=1.0±0.3 GeV/c2 for the axial mass value. With zero µΛK0 events observed, the 90% confidence level upper limit\(\sigma (\bar v_\mup \to \mu ^ +\Lambda {\rm K}^0 )< 2.0 \cdot 10^{ - 40} cm^2 \) is obtained. At the same time, we found that the cross section of reaction\(\bar v_\mup \to \mu ^ +\Lambda {\rm K}^0+ m\pi ^0 \) is equal to\(\left( {3.9\begin{array}{*{20}c}{ + 1.6}\\{ - 1.3}\\ \end{array} } \right) \cdot 10^{ - 40} cm^2 \).
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