Production of Weak Bosons in Association with Jets at Hadron Colliders. / Tietz, Stephan.

2013. 313 p.

Research output: ThesisMaster's Thesis

Unpublished

Abstract

This thesis investigates integrated and differential leading-order cross-sections for the production of weak bosons with up to two associated jets and leptonic decays at hadron colliders, i.e. pp/ppbar → (W− → l− νbar ) + n jets, pp/ppbar → (W+ → l+ ν ) + n jets, pp/ppbar → (Z → l− l+) + n jets and pp/ppbar → (Z → sum ν νbar ) + n jets. All cross-sections are calculated for accelerator setups Tevatron Run II, LHC with 7 TeV and 14 TeV, and PDF sets MSTW2008LO (90% C.L.) and CTEQ6L1. In all cases three different scale choices, static μ0 = MV , dynamic ET and HT , with a variation by a factor of four have been considered. Additionally, PDF uncertainties have been determined for the MSTW2008LO results. All results have been calculated using an amended version of the
MCFM 6.0 package and custom Python scripts.
The ratio between the integrated cross-sections for W+ and W− production with leptonic decay and the ratio between the integrated cross-sections for the two studied decays of the Z production have been calculated. I find that both are very stable for all scale choices. In contrast, for the Berends-Giele scaling a dependence on the choice of static/dynamic scale was observed.
Furthermore a variety of differential cross-sections have been calculated. This includes transverse momentum p_T and rapidity y for charged leptons and jets, missing transverse momentum p_T,miss , rapidity separation ∆y, separation in transverse angle ∆φ and ∆R. The distance observables use pT -ordered jets, charged leptons and missing momentum. For zero-jet processes the PDF and scale uncertainties decrease in the large invariant mass tails and for one and two-jet processes the uncertainties become larger in the tails. The latter was also observed for transverse momentum distributions.
The differential cross-sections are compared for the different scales and I find that different choices do not change the position of peaks or general features of the curves, but tails can differ. I show that varying the static scale by a factor of four is not always sufficient to cover the central values for dynamic scale choices. For invariant mass distributions, I show that the dynamic scale results are smaller than the static scale predictions and normally fall within the uncertainty envelope. Further, rapidity distributions are very stable with respect to different scale choices and only differ by a constant factor. The dynamic scales are well within the uncertainty envelope of the static scale. Comparisons with respect to different PDF sets showed a simple scaling for transverse observables.
The PDF uncertainties for MSTW2008LO (90% C.L.) were large enough to encompass the deviation between the two studied PDF sets for zero and one-jet processes, but not for two associated jets. For rapidity distributions, no uniform behaviour of CTEQ6L1 versus MSTW2008LO was observed. CTEQ6L1 can give a larger cross-section in the central/forward region, and the MSTW2008LO error underestimated this deviation.
Original languageEnglish
QualificationMPhil
Awarding Institution
Supervisors/Advisors
Award date1 Jun 2013
Publication statusUnpublished - 2013
This open access research output is licenced under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

ID: 17157873