Search for elastic muon-neutrino electron scattering

Recently many theoretical models have been postulated in an attempt to resolve the divergence of the classical current-current theory by unifying the weak and electromagnetic interactions. All these theories require neutral currents, heavy leptons, or both. One of these theories, that of Salam and Ward and Weinberg, gives specific predictions about the amplitudes of the neutral currents which are susceptible to experimental tests. In particular, using the model, t'Hooft [t'HO 71] has valuated the differential cross sections for the purely leptonic processes νμ + e- → νμ + e -; bar νμ + e- → bar νμ + e- which are forbidden to first order in the conventional Feynman Gell-Mann theory. The predicted cross sections are of the order of 10M41 cm2/electron at 1 GeV, depending on the Weinberg angle τw, which is the only free parameter of the theory. This paper discusses a search for these processes carried out in the large heavy liquid bubble chamber Gargamelle, useful volume 6.2 m3, filled with freon CG3Br, exposed to both the neutrino and antineutrino beams at the CERN PS. The large length of the chamber, 4.8 m, compared to the radiation length of freon, 11 cm, ensured that electrons were unambiguously identified