Titel: Higher-Order Resummation and Precision Predictions for Color-Singlet Transverse Momentum Distributions at the LHC
Sprache: Englisch
Autor*in: Billis, Georgios
Erscheinungsdatum: 2021
Tag der mündlichen Prüfung: 2021-10-22
Zusammenfassung: 
With the entire potential of the Large Hadron Collider (LHC) expected to be fully realized in the near future (High-Luminosity LHC), theoretical predictions that match the ever-increasing
precision of its experimental measurements are more imperative than ever. A central part of the LHC program is the study of differential distributions for color-singlet processes (e.g. Drell-Yan and Higgs production) since they allow for rigorous tests of the Standard Model and possible deviations from it. In this thesis, we focus on technical aspects of higher-order resummation for differential distributions as well as on providing precision predictions for color-singlet processes at the LHC in the framework of Soft-Collinear Effective Theory (SCET).

We first discuss the solution of the Sudakov evolution factor which is a central ingredient in every resummation framework. For the single gauge interaction case (QCD), all available approximate analytic solutions are studied with an emphasis on the accuracy they achieve. We find that at higher logarithmic orders none of the analytic methods meet the criteria for (sub-)percent level precision, and to this end we propose a semi-numerical method for its evaluation. We then apply this method and study the solution of the Sudakov factor in the presence of multiple gauge interactions (QCD-QED), where its precision is found to be at the permil level. An indispensable ingredient in this approach is an analytic solution of the coupled beta-functions for the running of the couplings, which we provide.

We then study the leading-power singular structure of the transverse momentum and 0-jettiness resolution variables for generic color-singlet processes in QCD. We exploit that the logarithmic structure of beam and soft functions is predicted by the renormalization group equations (RGE) they satisfy, and we solve them to three loops.
These are necessary ingredients for the transverse momentum and 0-jettiness resummation at N3LL' and N4LL as well as for the extension of the corresponding subtraction methods to N3LO. In addition, by employing consistency relations between different factorization limits, we predict the threshold limit of the transverse momentum and 0-jettiness beam function boundary coefficients at N3LO, results that go beyond their RGE-predicted terms. Furthermore, motivated by the nontrivial functional form of the full N3LO beam boundary terms, we propose a cost-optimal and precision-driven strategy for the numerical implementation of kernels that bear such functional signature.

Finally, we present predictions for the inclusive and fiducial gluon-fusion Higgs transverse momentum spectrum at N3LL'+N3LO at the LHC. For the latter, we compare to ATLAS preliminary data, finding good agreement throughout the spectrum. Part of our discussion focuses on the presence of linear (fiducial) power corrections that stem from the experimental cuts and how they can be included in the resummation framework. We then apply differential qT-subtractions to predict, for the first time, the Higgs total fiducial cross section at N3LO and improved by timelike and transverse momentum resummation. Of major importance for the precision of our results are the quadratic (nonsingular) power suppressed contributions, which we obtain via a dedicated fitting procedure. We conclude by discussing the caveats that apply to the commonly used qT-slicing method at this high perturbative order and in the presence of fiducial cuts. Both the transverse momentum spectrum and the total fiducial cross section are the highest-order predictions with a realistic description of all decay products at a hadron collider to date.
URL: https://ediss.sub.uni-hamburg.de/handle/ediss/9673
URN: urn:nbn:de:gbv:18-ediss-101383
Dokumenttyp: Dissertation
Betreuer*in: Tackmann, Frank
Enthalten in den Sammlungen:Elektronische Dissertationen und Habilitationen

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