Precision Calculations for Gauge-Boson Pair Production with a Hadronic Jet at Hadron Colliders

Kallweit, Stefan (2008): Precision Calculations for Gauge-Boson Pair Production with a Hadronic Jet at Hadron Colliders. Dissertation, LMU München: Fakultät für Physik

Abstract

Gauge-boson pair-production processes with an additional hadronic jet are of particular interest as background to Higgs and new-physics searches at hadron colliders. Moreover, they enable---besides genuine gauge-boson pair production---a direct analysis of the non-Abelian gauge-boson self-interactions in the electroweak sector. In this work we provide precision calculations for the processes pp->VV+jet+X. In detail, corrections to WW+jet, ZZ+jet, and WZ+jet production are evaluated at next-to-leading-order in the strong coupling (NLO QCD). Particular care has to be taken when treating the infrared singularities arising in the virtual and real corrections. The FormCalc/LoopTools package is applied for the virtual corrections, where dimensionally regularized infrared-divergent integrals are added to the FF library which is used for the regular ones. The real-emission matrix elements are evaluated in terms of helicity amplitudes in the Weyl--van-der-Waerden formalism. The Catani--Seymour dipole subtraction formalism mediates the cancellation of infrared divergences between the two contributions. To perform the numerical integration a multi-channel Monte Carlo integrator is written in C++, which is designed to meet the requirements of integrating cross sections in the dipole subtraction formalism. For all gauge-boson assignments, the NLO QCD corrections significantly stabilize the artificial dependence of the leading-order (LO) cross sections on renormalization and factorization scales for Tevatron. For LHC, however, only a modest reduction of the scale dependence results unless a veto on a second hard jet is applied. Beyond investigating the production processes, leptonic decays of the gauge bosons are considered. To this end, a full amplitude calculation including resonant and non-resonant contributions to the leptonic final states, a simple narrow-width approximation (NWA), and an improved version of the NWA that takes into account spin correlations are performed at LO. Comparing these approaches the improved NWA turns out to deliver an appropriate approximation to the decays at a reasonable level of accuracy. Thus, an NLO QCD calculation to VV+jet including leptonic decays is performed in the framework of the improved NWA. Several results on differential cross sections for quantities of the jet and the decay leptons are presented. For WW+jet, we discuss both proton--proton collisions at LHC and proton--antiproton collisions at Tevatron. For WZ+jet and ZZ+jet, however, the cross sections at Tevatron are too small, so only results for LHC are presented. The Monte Carlo generator developed in this thesis can be used as a tool in data analysis at LHC and Tevatron.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 21. November 2008
• 1. Bericht­erstatter:in: Dittmaier, Stefan