Search for right-handed currents in muon decay

We report preliminary results of an experiment designed to measure the mass of the right-handed intermediate vector boson. The presence of such a particle in electroweak interactions is predicted by left-right symmetric gauge theories. The experiment measures the momentum spectrum of the positrons from the decay at rest of (1) longitudinally polarized muons produced in the decay at rest of π+ → μ+nu (polarization P/sub μ/) and (2) unpolarized muons. The endpoints of these two spectra are used to determine the quantity xi P/sub μ/ where xi is a Michel parameter. This product is related to the ratio of the mass of left and right handed W and to the phase between the two helicity states. We measure, at the 90% CL, 1 - delta/rho < 0.0041 and infer the mass M(W/sub R/) > 380 GeV/c2