Wuppertal, Univ., Diss., 2003. / Computerdatei im Fernzugriff.

München, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

München, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Wuppertal, Universiẗat, Diss., 1999.

Wuppertal, Universiẗat, Diss., 1996.

Wuppertal, University, Diss., 2003.

Wuppertal, Universiẗat, Diss., 2000.

No description available.

The analysis of the Higgs boson decay into the pairs of tau leptons H → ττ is presented. In the scope of this thesis, only the tau leptons decaying purely lep- tonically are considered. This analysis is performed using data recorded from the proton-proton collisions at a center-of-mass energy √ s = 13 TeV by the ATLAS detector at the Large Hadron Collider and correspond to the integrated lumi- nosity of 36.1 fb−1 . The Boosted Decision Trees (BDT) multivariate technique was used in order to provide a classification of events. Datasets considered in this analysis consisted of the triggered, reconstructed and calibrated events. In addition, events had to pass the pre-selection criteria and were separated into four categories. Our main contribution to this analysis is based on developing and incorporating techniques used in the process of BDT training and evaluation. The performed analysis presented in this thesis is blinded. Therefore, the Monte Carlo simulation was used instead of real data in the Maximum Likelihood Fit in order to determine the expected significance. For the H → ττ leptonic channel, the expected signal significance was measured to be 1.16 σ. 1

The electroweak standard model, as well-known, has been remarkably successful in describing a broad spectrum of high energy physics and has also given a satisfactory and consistent theoretical description of all the experimental data which has been obtained so far. The aim of the present work is to investigate some of the most important processes associated with the standard model which involve the charged intermediate bosons W(^±), the neutral intermediate boson Z, the pair production of weak gauge bosons and the Higgs boson. First of all we start with the study of the effect of the strong interaction on the direct production of weak gauge boson production at hadron colliders. We calculate the first order perturbative QCD corrections O(a(_s)) to the lowest order cross sections for photon and Z pair production at hadron colliders. The calculation contains divergences, represented in dimensional regularisation by poles of order O(1/ϵ) and O(1/ϵ(^2)), where ϵ = 4-n(_2). The order O(1/ϵ(^2)) terms are eliminated when real and virtual corrections are combined, and the remaining 0(1/ϵ) corrections will be absorbed into the quark momentum distribution functions. We then study the production rate of weak gauge boson pairs for proton- proton and proton-antiproton colliders using single and double parton scattering mechanisms. We extrapolate to the next generation of hadron colliders with centre-of-mass energy E(_cm)= 10-200 TeV. We find comparable values for the single and double scattering cross sections at very high energies. To expand our investigation, we study also the production rate of multiple gauge bosons at hadron supercolliders using the double parton scattering mechanism. These kinds of processes are important and represent a potential significant background for Higgs boson production. Finally, and for completeness, we study Higgs boson phenomenology, which now forms a substantial part of the physics program at the next generation of high-energy colliders. The calculation covers the production rate of single and double Higgs production at hadron colliders via gluon-gluon fusion, their branching ratios and decay widths.