Untersuchung inklusiver CP-Asymmetrien in B0-Zerfällen

The object of the present thesis is the search for CP-violating effects in the mixing of neutral B mesons. For this the time-dependent CP asymmetry in the decay of completely inclusively reconstructed B0 mesons was studied. The basis of the analysis were about 4.1 millions hadronic Z decays, which were token up in the years 1991-1995 with the ALEPH detector at the e+e- storage ring LEP at CERN. From the data b hadron decays were inclusively reconstructed by means of a search for secondary decay vertices. By a fit to the decay-time spectra od identified B0 and anti B0 decays the following value of the semileptonic asymmetry in the Bd0- anti Bd0 system could be determined: aCP=0.016±0.034(stat.)±0.009(syst.). This value can be alternatively interpreted as a measurement of the CP-violating parameter Re εB: Re εB/(1+ vertical stroke εB vertical stroke 2)=0.004±0.009(stat.)±0.002(syst.). Furthermore a combination of the results of this analysis with a further ALEPH measurement was performed. The value of aCP determined from this, which was obtained under regardment of the statistical correlation of both measurements as well as correlated systematic uncertainties, is: aCP=-0.013±0.026. The present result is compatible with the standard model prediction and yields no significant hint to CP violation in the Bd0- anti B0d mixing. (orig.)