ResBos2 : precision resummation for the LHC ERA
Isaacson, Joshua Paul
Standard model (Nuclear physics)
Quantum chromodynamics
Particles (Nuclear physics)
Large Hadron Collider (France and Switzerland)
Physics
With the precision of data at the LHC, it is important to advance theoretical calculations to match it. Previously, the ResBos code was insufficient to adequately describe the data at the LHC. This requires an advancement in the ResBos code, and led to the development of the ResBos2 package. This thesis discusses some of the major improvements that were implemented into the code to advance it and prepare it for the precision of the LHC.The resummation for color singlet particles is improved from approximate NNLL+NLO accuracy to an accuracy of N$^3$LL+NNLO accuracy. The ResBos2 code is validated against the calculation of the total cross-section for Drell-Yan processes against fixed order calculations, to ensure that the calculations are performed correctly. This allows for a prediction of the transverse momentum and $\phi^*_{\eta}$ distributions for the $Z$ boson to be consistent with the data from ATLAS at a collider energy of $\sqrt{s}=8$ TeV. Also, the effects of choice of resummation scheme are investigated for the Collins-Soper-Sterman and Catani-deFlorian-Grazzini formalisms. It is shown that as long as the calculation of each of these is performed such that the order of the $B$ coefficient is exactly 1 order higher than that of the $C$ and $H$ coefficients, then the two formalisms are consistent. Additionally, using the improved theoretical prediction will help to reduce the theoretical uncertainty on the mass of the $W$ boson, by reducing the uncertainty in extrapolating the $\frac{d\sigma}{dp_T^W}$ distribution from the data for the $\frac{d\sigma}{dp_T^Z}$ distribution by taking the ratio of the theory predictions for the $Z$ and $W$ transverse momentum. In addition to improving the accuracy of the color singlet final state resummation calculations, the ResBos2 code introduces the resummation of non-color singlet states in the final state. Here the details for the Higgs plus jet calculation are illustrated as an example of one such process. It is shown that it is possible to perform this resummation, but the resummation formalism needs to be modified in order to do so. The major modification that is made is the inclusion of the jet cone-size dependence in the Sudakov form factor. This result resolves, analytically, the Sudakov shoulder singularity. The results of the ResBos2 prediction are compared to both the fixed order and parton shower calculations. The calculations are shown to be consistent for all of the distributions considered up to the theoretical uncertainty. As the LHC continues to increase their data, and their precision on these observables, the ability to have analytic resummation calculations for non-color singlet final states will provide a strong check of perturbative QCD.Finally, the calculation of the terms needed to match to N$^3$LO are done in this work. Once the results become sufficiently publicly available for the perturbative calculation, the ResBos2 code can easily be extended to include these corrections, and be used as a means to predict the total cross-section at N$^3$LO as well.
Includes bibliographical references (pages 220-240)
Online resource; title from PDF title page (ProQuest viewed on June 12, 2019)
Yuan, C.-P.
Schmidt, Carl
Brock, Raymond
Piermarocchi, Carlo
O'Shea, Brian
2017
text
Electronic dissertations
Academic theses
application/pdf
1 online resource (xvi, 240 pages) : illustrations
isbn:9780355514698
isbn:0355514699
umi:10684340
local:Isaacson_grad.msu_0128D_15737
en
Attribution 4.0 International
Ph.D.
Doctoral
Physics - Doctor of Philosophy
Michigan State University