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Title
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Improving the accuracy of transverse momentum dependent parton branching methods for collider physics
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Author
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Abstract
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| This thesis presents several studies on calculations for high-energy proton-proton collisions using the Parton Branching (PB) method for the evolution of transverse momentum dependent parton distribution functions (TMDs). The PB method allows to perform both inclusive and exclusive calculations of collision final states by means of Monte Carlo techniques. Evolution of TMDs in the PB method allows for the resummation of soft gluons by the Sudakov form factor. The implementation of PB TMDs in the TMDlib library and the implementation of the backward PB Sudakov form factor in the CASCADE3 Monte Carlo event generator allows for the calculation of a wide variety of particle collision processes in a wide kinematic range. We examine the PB method, focusing on the Sudakov form factor and the soft-gluon resolution scale. By extending the emission phase space with longitudinal splitting fractions z approaching one, we achieve accurate perturbative resummation and a non-perturbative contribution to the evolution. A dynamical resolution scale separates resolvable and non-resolvable phase space regions, acting as a boundary between these perturbative and non-perturbative domains. We show that PB evolution with next-to-leading order (NLO) splitting functions achieves next-to-leading logarithmic (NLL) accuracy in soft-gluon resummation. The implementation of the physical (or effective) soft-gluon coupling enhances Sudakov resummation towards next-to-next-to-leading logarithmic (NNLL) accuracy. Application to the transverse momentum spectrum of the Z-boson in the Drell-Yan (DY) process shows the effect of implementing the physical coupling. Non-perturbative contributions of the Sudakov are illustrated through the extraction of the Collins-Soper (CS) kernel. These extractions highlight the influence of both the emission phase space and the scale of the strong coupling in TMD evolution on the large b behavior of the CS kernel. Combining higher order matrix element calculations with PB TMDs and TMD shower is done through matching and merging techniques. Azimuthal correlations of high transverse momentum jets in di-jet production and boson-jet production are calculated using PB TMDs matched to NLO matrix elements. QCD predictions for final states with multiple jets in hadron collisions make use of multi-jet merging methods. These methods consistently combine the contributions from hard scattering matrix elements with different parton multiplicities and parton showers. Calculations of jet transverse momentum and jet multiplicity distributions, as well as highly non-trivial jet event shapes, are performed with the recently developed TMD merging method. We investigate theoretical predictions for Z-boson plus jets production using multi-jet merging algorithms. Our analysis focuses on the differential jet rates (DJRs) and their discontinuities, which allows us to develop a method for quantitatively analyzing the merging algorithm and its dependence on the merging scale by varying invariant di-lepton masses. |
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Language
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English
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Publication
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Antwerp
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Universiteit Antwerpen, Faculteit Wetenschappen, Departement Fysica
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2024
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DOI
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10.63028/10067/2051600151162165141
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Volume/pages
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xii, 209 p.
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Note
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Hautmann, Francesco [Supervisor]
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Van Mechelen, Pierre [Supervisor]
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Full text (open access)
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