Measurement of the reaction e+e- → τ+τ- with MARK J at PETRA

The present thesis arose from the evaluation of the data of the MARK J experiment at the e+e- storage ring PETRA at c.m. energies of 14-46.78 GeV. Studied was the reaction e+e- → τ++ τ- whereby only events were regarded in which one tau decayed into a muon, the other into a hadronic or electronic shower. After all cuts 2197 events were retained. From these the cross section was determined in very good agreement with QED to: = 0.99 ± 0.02 ± 0.05. The point shape of the interaction is shown in the cutoff parameters Λ+ > 262 GeV and Λ- > 206 GeV. Using this and assuming the validity of QED so Rττ represents a measurement of the branching ratio of the decay τ → μνanti ν: Br(τ → μνanti ν) = 17.4 ± 1.0%. The influence of the weak interaction is shown in the measured charge asymmetry Aττ in agreement with the prediction of the Glashow-Salam-Weinberg theory. The axial-vector coupling constant of the tau has been determined in this experiment to: gaτ = -0.45 ± 0.13. The V-A structure of the tau decay is hardened by a determination of the Michel parameter and it is studied how far limits for lepton number violation can be given. Because the used signature also occurs in the decay of many particles of yet hypothetical models these were studied and lower limits for the masses of these particles determined. So could be shown that for a heavy sequential lepton of a new generation ML > 22.4 GeV is valid. Similarly the production of Higgs and SUSY particles was confined. (orig./HSI)