Measurement of Differential Cross-Sections in the ttbar

The analysis presented in this thesis focuses on the measurement of kinematic distributions of top quarks produced in pairs and decaying into the lepton+jets final state. In detail, the top quark transverse momentum distribution and the top-antitop pair invariant mass spectrum are studied, focusing on comparisons to the predictions from perturbative quantum chromodynamic. The top quark is special in being the heaviest elementary particle know at the time of writing this thesis, and is an excellent object for testing the Standard Model of elementary particles. It offers a window on properties of a bare heavy quark and can serve as a laboratory to look for new physics in terms of possible anomalous production mechanism, decay modes and shapes of kinematic variables. The analysis was performed with data recorded by the D0 Run II detector at Fermilab. The presented thesis was defended at the Faculty of Mathematics and Physics at the Charles University in Prague in April 2009.