Reconstruction of B hadron decays at DELPHI

Abstract

This thesis describes three analyses related to heavy quarks.

The analysis with the largest impact is the extraction of parameters of heavy quark decays using the lepton energy spectrum and the hadronic mass spectrum in semileptonic B decays. The extraction of the parameters allows to test the framework used to theoretically describe the decay of heavy mesons, and more accurate knowledge of the parameter values results in greater accuracy in the determination of the element |Vcb| of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. The determination described in this thesis is important, since it is so far the only one where the full lepton energy spectrum has been used. The other determinations are based on using only a part of the spectrum. The first extraction of the parameters in the kinetic mass scheme was based on the statistical moments of the lepton energy spectrum and hadronic mass spectrum measured using the data collected at DELPHI.

In the second analysis, the angular distribution of fragmentation particles in Z → bb̅ and Z → cc̅ events was studied using the DELPHI data. The analysis gave the first direct experimental evidence of the dead cone effect, or the depletion of fragmentation particles at small emission angles, predicted by perturbative quantum chromodynamics.

The third analysis is a simulation study of top quark pair production at a possible future e+e− linear collider with a 3 TeV center-of-mass energy. The study allowed to estimate the accuracies with which the cross-section and forward-backward asymmetry could be measured.