New Results On Inverse Muon Decay and Low Multiplicity Reactions

New results on inverse muon decay and coherent charged pion production by neutrinos are presented. The data come from the CHARM-II neutrino detector operated at the CERN wide-band neutrino beam. High-statistics data samples of 14500 inverse muon decay events and 3500 νμe elastic scattering events allow the determination of the electroweak parameters from the ratio of the cross-sections of neutral-to-charged-current neutrino electron scattering. The best fit values of the electroweak mixing angle sin 2 Ω w and the relative coupling strength ϱ of neutral and charged current are: sin 2 Ω w = 0.237 ± 0.014 and ϱ = 0.987 ± 0.042 . In the second topic, coherent single charged pion production was measured in neutrino and antineutrino beams. The measured cross-sections, averaged over the wide-band beam spectra and the glass target nuclei composition, are: σ(νμA → μ−π+A) = (51 ± 10) × 10−40 cm2 nucleus and σ( ν μ A → μ + π − A) = (43 ± 9) × 10 −40 cm 2 nucleus. The energy dependence shows the expected flattering of the cross-sections at high energy.