Estudio del canal electrónico de desintegración del lepton tau en LEP con el detector DELPHI

This thesis presents a study of the decays \tau\rightarrow e\nu\overline{\nu} identified after a selection of \tau^+\tau^- events produced in e^+e^- collisions at LEP. These collisions, predominantly mediated by a Z^0 boson, offer a good laboratory for the study of weak current parameters. Moreover, the decays of the tau lepton, which proceed via a W boson, increase the possibilities of our study. The experimental observables, which imply an indirect knowledge of the coupling constants, include the polarization asymmetry and the forward-backward polarization asymmetry. The branching ratio of the electronic decay of the \tau lepton (18.24\pm0.28\pm0.32)\%) derives a measurement of the strong coupling constant \alpha_s at the scale of the Z^0 boson mass (0.118^{+0.004}_{-0.006}\pm0.006) and a test of lepton universality in weak currents (\frac{g_{\tau}}{g_{\mu}}=1.000\pm0.014). The spectra of momenta and electromagnetic energy depositions used as estimates of the energy of the electron allow to measure the polarization asymmetries (P_{\tau}=-0.16\pm0.0 9\pm0.05 and A^{FB}_{pol}=-0.19\pm0.09\pm0.01) giving subsequent values for the effective sin^2\theta_W (0.230\pm0.013 and 0.218\pm0.015).