Study of production and disintegration of tau+tau- pairs at PETRA

The subject of this thesis is the study of the production and decay of tau+tau- pairs in e+e- collisions at total centre of mass energies of 14, 22 and 34 GeV. The experiment was carried out at the PETRA e+e- collider, using the CELLO detector. The processes studied allows firstly to test quantum electrodynamics. The measured total cross-section shows the 1/s behaviour characteristic of point-like particles. A first independent confirmation of spin 1/2 for the tau is obtained by measuring the angular distribution which is compatible with (1 + cos2 theta). At √s = 34 GeV, the effect of electro-weak interference can clearly be seen. Experimentally a forward-backward asymmetry of -(10.2 +- 5.2)% is observed, from which a value for the axial vector coupling constant of asub(tau) = -1.1 +- .6 may be deduced (the prediction of the standard model is -1). Comparison of this value with asub(e), and asub(u) allows a check to be made of the lepton universality hypothesis. Topological branching ratio for tau decays into 1, 3, 5 charged particles have been measured and compared to predictions