| 11. |
- Campanario, Francisco, et al.
(författare)
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Stress testing the vector-boson-fusion approximation in multijet final states
- 2018
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Ingår i: Physical Review D. - 2470-0010. ; 98:3
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Tidskriftsartikel (refereegranskat)abstract
- We consider electroweak Higgs plus three jets production at NLO QCD beyond strict VBF acceptance cuts. We investigate, for the first time, how accurate the VBF approximation is in these regions and within perturbative uncertainties by a detailed comparison of full and approximate calculations. We find that a rapidity gap between the tagging jets guarantees a good approximation, while an invariant mass cut alone is not sufficient, which needs to be confronted with experimental choices. We also find that a significant part of the QCD corrections can be attributed to Higgs-Strahlungs-type topologies.
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| 12. |
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| 13. |
- Cormier, Kyle, et al.
(författare)
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Parton showers and matching uncertainties in top quark pair production with Herwig 7
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:11
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate the theoretical uncertainties in next-to-leading order plus parton shower predictions for top quark pair production and decay in hadronic collisions. Our work is carried out using the Herwig 7 event generator and presents an in-depth study of variations in matching schemes with two systematically different shower algorithms, the traditional angular-ordered and alternative dipole shower. We also present all of the required extensions of the Herwig dipole shower algorithm to properly take into account quark mass effects, as well as its ability to perform top quark decays. The predictions are compared at parton level as well as to Large Hadron Collider data, including in the boosted regime. We find that the regions where predictions with a non-top-quark-specific tune differ drastically from data are plagued by large uncertainties which are consistent between our two shower and matching algorithms.
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| 14. |
- Gras, Philippe, et al.
(författare)
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Systematics of quark/gluon tagging
- 2017
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2017:7
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Tidskriftsartikel (refereegranskat)abstract
- By measuring the substructure of a jet, one can assign it a “quark” or “gluon” tag. In the eikonal (double-logarithmic) limit, quark/gluon discrimination is determined solely by the color factor of the initiating parton (CF versus CA). In this paper, we confront the challenges faced when going beyond this leading-order understanding, using both parton-shower generators and first-principles calculations to assess the impact of higher-order perturbative and nonperturbative physics. Working in the idealized context of electron-positron collisions, where one can define a proxy for quark and gluon jets based on the Lorentz structure of the production vertex, we find a fascinating interplay between perturbative shower effects and nonperturbative hadronization effects. Turning to proton-proton collisions, we highlight a core set of measurements that would constrain current uncertainties in quark/gluon tagging and improve the overall modeling of jets at the Large Hadron Collider.
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| 15. |
- Keppeler, Stefan, et al.
(författare)
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Wigner 6j symbols with gluon lines : completing the set of 6j symbols required for color decomposition
- 2024
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2024:5
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Tidskriftsartikel (refereegranskat)abstract
- We construct a set of Wigner 6j symbols with gluon lines (adjoint representations) in closed form, expressed in terms of similar 6j symbols with quark lines (fundamental representations). Together with these Wigner 6j symbols with quark lines, this gives a set of 6j symbols sufficient for treating QCD color structure for any number of external particles, in or beyond perturbation theory. This facilitates a complete treatment of QCD color structure in terms of orthogonal multiplet bases, without the need of ever explicitly constructing the corresponding bases. We thereby open up for a completely representation theory based treatment of SU(N) color structure, with the potential of significantly speeding up the color structure treatment.
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| 16. |
- Lifson, Andrew, et al.
(författare)
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One-loop calculations in the chirality-flow formalism
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In a few recent papers we introduced the chirality-flow formalism, which was shown to make calculations of tree-level Feynman diagrams simple and transparent. Chirality flow, which is based on the spinor-helicity formalism, allows to often immediately analytically write down a tree-level Feynman diagram in terms of spinor inner products. In this paper, we argue that there is also a significant simplification of the Lorentz structure at the one-loop level, at least when using the four-dimensional formulation of the four-dimensional helicity scheme. Additionally, we find that the possible terms in a tensor decomposition of loop integrals are highly constrained, and therefore the tensor reduction procedure is simplified.
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| 17. |
- Olsson, Jimmy, et al.
(författare)
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Resampling algorithms for high energy physics simulations
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media Deutschland GmbH. - 1434-6044 .- 1434-6052. ; 80:10
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the method of interleaved resampling in the context of parton showers can tremendously improve the statistical convergence of weighted parton shower evolution algorithms. We illustrate this by several examples showing significant statistical improvement.
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| 18. |
- Plätzer, Simon, et al.
(författare)
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Color matrix element corrections for parton showers
- 2018
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2018:11
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effects of keeping the full color structure for parton emissions in parton showers for both LEP and LHC. This is done within the Herwig 7 dipole shower, and includes gluon emission, gluon splitting, initial state branching processes, as well as hadronization. The subleading Nc terms are included as color matrix element corrections to the splitting kernels by evolving an amplitude-level density operator and correcting the radiation pattern for each parton multiplicity, up to a fixed number of full color emissions, after which a standard leading color shower takes over. Our results are compared to data for a wide range of LEP and LHC observables and show that the subleading Nc corrections tend to be small for most observables probing hard, perturbative dynamics, for both LEP and LHC. However, for some of these observables they exceed 10%. On soft physics we find signs of significantly larger effects.
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| 19. |
- Valassi, Andrea, et al.
(författare)
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Challenges in Monte Carlo Event Generator Software for High-Luminosity LHC
- 2021
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Ingår i: Computing and Software for Big Science. - : Springer Science and Business Media LLC. - 2510-2044 .- 2510-2036. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- We review the main software and computing challenges for the Monte Carlo physics event generators used by the LHC experiments, in view of the High-Luminosity LHC (HL-LHC) physics programme. This paper has been prepared by the HEP Software Foundation (HSF) Physics Event Generator Working Group as an input to the LHCC review of HL-LHC computing, which has started in May 2020.
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