Electroweak boson production at small transverse momentum in hadron collisions
The resummation of double-logarithmic perturbative contributions produced by soft- gluon radiation (Sudakov resummation) has proved to be an important tool for enlarging the applications of perturbative QCD to a wider range of kinematical regions. In particular, a complete description of W and Z boson production at high-energy hadron colliders requires the resummation of large double logarithms that dominate the transverse momentum (p(_r)) distribution at small p(_r). This can be performed either directly in transverse momentum space or in impact parameter (Fourier transform) b space. The b space method succeeds in resumming all the leading and sub-leading logarithmic terms, but does not allow a smooth transition to fixed-order dominance at high transverse momenta. In contrast, the pr space approach experiences difficulties with resumming more sub-leading logarithms. This thesis concentrates on developing the p(_r) space formalism which completely resums the first four towers of logarithms. The number of fully resummed towers is the same as for the b space method. The results are compared, both analytically and numerically, with the original b space result as well as with results of other p(_r) space methods. Parametrization of the non-perturbative effects in p(_r) space is discussed. Given recent Tevatron data on Z boson production we find good agreement between the data and the theoretical predictions. Using the same formalism, the transverse momentum distributions are also calculated for W and Z boson production at the LHC. Finally, we discuss production of like-sign W pair production in the context of double parton scattering at the LHC.