Master Thesis: A Matrix-Element-Based Modification of the Parton Shower LU TP 98 9 Gabriela Miu Abstract: The transverse momentum distribution of W+/W- bosons at hadron colliders is well described by a parton-shower model for small pT values, but not for large ones. This article is an attempt to give a better description of the distribution by using corrections derived from the matrix-element formalism. The parton shower for qqbar->W+/W- has been modified to resemble the matrix elements of qqbar->gW and qg->qW at large pT values. Comparisons between different approaches are presented at sqrt(s)=1800 GeV. The results are also compared with experimental data from the D0 collaboration at Fermilab.