A measurement of the V-A x V-A structure of the weak charged current in semileptonic b decays and missing energy measurements

The polarization of the W-propagator in semileptonic b decays is measured with the 13 experiment at LEP via simultaneous observation of the charged lepton and the neutrino spectrum. The polarization is seen with more than 3 standard deviations and found to be in agreement with the V-AxV-A structure. The measurement excludes the V+Ax V-A polarization with more than 6 standard deviations. Furthermore, the branching ratio in B_, vX is measured and found to be 22.7%±0.8%(stat.)±l.5%(syst.) which corresponds to a branching ratio of B_,evX of 10.1%±0.8%.