An upper limit to the cross section for the reaction anti γsub(μ)e-→anti γsub(μ)e- at SPS energies

Candidates for the purely leptonic process antiγsub(μ)e-→antiγsub(μ)e- have been searched for in the bubble chamber Gargamelle exposed to the CERN-SPS antineutrino wide-band beam. No single e-, of energy greater than 1 GeV, was found in a total of 230 000 pictures, corresponding to 7400 charged current events. This leads to an upper limit for the observed cross section of sigmasub(obs)<1.6x10-42(Esub(anti γ)/GeV)cm2(90%C.L.). Interpretation of this value in terms of the standard Weinberg-Salam model yields an upper limit to the mixing parameter sin2thetasub(W)<0.39 at 90%C.L. (Auth.)