| 1. |
- 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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| 2. |
- Bothmann, Enrico, et al.
(författare)
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A standard convention for particle-level Monte Carlo event-variation weights
- 2023
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Ingår i: SciPost Physics Core. - 2666-9366. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Streams of event weights in particle-level Monte Carlo event generators are a convenient and immensely CPU-efficient approach to express systematic uncertainties in phenomenology calculations, providing systematic variations on the nominal prediction within a single event sample. But the lack of a common standard for labelling these variation streams across different tools has proven to be a major limitation for event-processing tools and analysers alike. Here we propose a well-defined, extensible community standard for the naming, ordering, and interpretation of weight streams that will serve as the basis for semantically correct parsing and combination of such variations in both theoretical and experimental studies.
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| 3. |
- Gellersen, Leif, et al.
(författare)
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Disentangling soft and collinear effects in QCD parton showers
- 2022
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Ingår i: Physical Review D. - 2470-0010. ; 105:11
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a method for the separation of soft and collinear logarithms in QCD parton evolution at O(αs2) and at leading color. Using an implementation of the technique in the dire parton shower, we analyze the numerical impact of genuine triple-collinear corrections from quark pair emission in e+e-→ hadrons.
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| 4. |
- Hoeche, Stefan, et al.
(författare)
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Combining parton showers and NNLO matrix elements
- 2015
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Ingår i: Proceedings, 50th Rencontres de Moriond, QCD and high energy interactions: La Thuile, Italy, March 21-28, 2015. ; , s. 135-138
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Höche, Stefan, et al.
(författare)
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Simulation of vector boson plus many jet final states at the high luminosity LHC
- 2019
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Ingår i: Physical Review D. - 2470-0010. ; 100:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel event-generation framework for the efficient simulation of vector boson plus multijet backgrounds at the high-luminosity LHC and at possible future hadron colliders. Message passing interface parallelization of parton-level and particle-level event generation and storage of parton-level event information using the HDF5 data format allow us to obtain leading-order merged Monte Carlo predictions with up to nine jets in the final state. The parton-level event samples generated in this manner correspond to an integrated luminosity of 3 ab-1 and are made publicly available for future phenomenological studies.
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| 6. |
- Sjöstrand, Torbjörn, et al.
(författare)
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An introduction to PYTHIA 8.2
- 2015
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Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655. ; 191, s. 159-177
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Tidskriftsartikel (refereegranskat)abstract
- The PYTHIA program is a standard tool for the generation of events in high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multiparticle final state. It contains a library of hard processes, models for initial- and final-state parton showers, matching and merging methods between hard processes and parton showers, multiparton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and several interfaces to external programs. PYTHIA 8.2 is the second main release after the complete rewrite from Fortran to C++, and now has reached such a maturity that it offers a complete replacement for most applications, notably for LHC physics studies. The many new features should allow an improved description of data. New version program summary Program title: PYTHIA 8.2 Catalogue identifier: ACTU_v4_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ACTU_v4_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence, version 2 No. of lines in distributed program, including test data, etc.: 478360 No. of bytes in distributed program, including test data, etc.: 14131810 Distribution format: tar.gz Programming language: C++. Computer: Commodity PCs, Macs. Operating system: Linux, OS X; should also work on other systems. RAM: 10 megabytes Classification: 11.2. Does the new version supersede the previous version?: Yes Catalogue identifier of previous version: ACTU_v3_0 Journal reference of previous version: Comput Phys. Comm. 178 (2008) 852 Nature of problem: High-energy collisions between elementary particles normally give rise to complex final states, with large multiplicities of hadrons, leptons, photons and neutrinos. The relation between these final states and the underlying physics description is not a simple one, for two main reasons. Firstly, we do not even in principle have a complete understanding of the physics. Secondly, any analytical approach is made intractable by the large multiplicities. Solution method: Complete events are generated by Monte Carlo methods. The complexity is mastered by a subdivision of the full problem into a set of simpler separate tasks. All main aspects of the events are simulated, such as hard-process selection, initial- and final-state radiation, beam remnants, fragmentation, decays, and so on. Therefore events should be directly comparable with experimentally observable ones. The programs can be used to extract physics from comparisons with existing data, or to. study physics at future experiments. Reasons for new version: Improved and expanded physics models. Summary of revisions: Hundreds of new features and bug fixes, allowing improved modelling. Restrictions: Depends on the problem studied. Running time: 10-1000 events per second, depending on process studied. (C) 2015 Elsevier B.V. All rights reserved.
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| 7. |
- Andersen, Jeppe R., et al.
(författare)
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A Positive Resampler for Monte Carlo events with negative weights
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:11
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Tidskriftsartikel (refereegranskat)abstract
- We propose the Positive Resampler to solve the problem associated with event samples from state-of-the-art predictions for scattering processes at hadron colliders typically involving a sizeable number of events contributing with negative weight. The proposed method guarantees positive weights for all physical distributions, and a correct description of all observables. A desirable side product of the method is the possibility to reduce the size of event samples produced by General Purpose Event Generators, thus lowering the resource demands for subsequent computing-intensive event processing steps. We demonstrate the viability and efficiency of our approach by considering its application to a next-to-leading order + parton shower merged prediction for the production of a W boson in association with multiple jets.
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| 8. |
- Andersen, Jeppe R., et al.
(författare)
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Les Houches 2017: Physics at TeV Colliders Standard Model Working Group Report
- 2018. - 07977
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This Report summarizes the proceedings of the 2017 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt with (I) new developments relevant for high precision Standard Model calculations, (II) theoretical uncertainties and dataset dependence of parton distribution functions, (III) new developments in jet substructure techniques, (IV) issues in the theoretical description of the production of Standard Model Higgs bosons and how to relate experimental measurements, (V) phenomenological studies essential for comparing LHC data from Run II with theoretical predictions and projections for future measurements, and (VI) new developments in Monte Carlo event generators.
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| 9. |
- Belyaev, Alexander, et al.
(författare)
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Probing dark matter with disappearing tracks at the LHC
- 2021
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Ingår i: Physical Review D. - 2470-0010. ; 103:9
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Tidskriftsartikel (refereegranskat)abstract
- Models where dark matter is a part of an electroweak multiplet feature charged particles with macroscopic lifetimes due to the charged-neutral mass split of the order of pion mass. At the Large Hadron Collider, the ATLAS and CMS experiments will identify these charged particles as disappearing tracks, since they decay into a massive invisible dark matter candidate and a very soft charged Standard-Model particle, which fails to pass the reconstruction requirements. While ATLAS and CMS have focused on the supersymmetric versions of these scenarios, we have performed here the reinterpretation of the latest ATLAS disappearing track search for a suite of dark matter multiplets with different spins and electroweak quantum numbers. More concretely, we consider the cases of the inert two Higgs doublet, minimal fermion dark matter and vector triplet dark matter models. Our procedure is validated by using the same wino and Higgsino benchmark models employed by the ATLAS Collaboration. We have found that with the disappearing track signature, one can probe a vast portion of the parameter space, well beyond the reach of prompt missing energy searches (notably monojets). We provide tables with the upper limits on the cross section and efficiencies in the lifetime - a dark matter mass plane for all the models under consideration, which can be used for an easy recast for similar classes of models. Moreover, we provide the recasting code employed here, as part of the public LLP recasting repository.
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| 10. |
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| 11. |
- Bright-Thonney, Samuel, et al.
(författare)
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Systematic quark/gluon identification with ratios of likelihoods
- 2022
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2022:12
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Tidskriftsartikel (refereegranskat)abstract
- Discriminating between quark- and gluon-initiated jets has long been a central focus of jet substructure, leading to the introduction of numerous observables and calculations to high perturbative accuracy. At the same time, there have been many attempts to fully exploit the jet radiation pattern using tools from statistics and machine learning. We propose a new approach that combines a deep analytic understanding of jet substructure with the optimality promised by machine learning and statistics. After specifying an approximation to the full emission phase space, we show how to construct the optimal observable for a given classification task. This procedure is demonstrated for the case of quark and gluons jets, where we show how to systematically capture sub-eikonal corrections in the splitting functions, and prove that linear combinations of weighted multiplicity is the optimal observable. In addition to providing a new and powerful framework for systematically improving jet substructure observables, we demonstrate the performance of several quark versus gluon jet tagging observables in parton-level Monte Carlo simulations, and find that they perform at or near the level of a deep neural network classifier. Combined with the rapid recent progress in the development of higher order parton showers, we believe that our approach provides a basis for systematically exploiting subleading effects in jet substructure analyses at the Large Hadron Collider (LHC) and beyond.
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| 12. |
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| 13. |
- Butterworth, J., et al.
(författare)
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Les Houches 2013: Physics at TeV Colliders: Standard Model Working Group Report
- 2014
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Konferensbidrag (refereegranskat)abstract
- This Report summarizes the proceedings of the 2013 Les Houches workshop on Physics at TeV Colliders. Session 1 dealt primarily with (1) the techniques for calculating standard model multi-leg NLO and NNLO QCD and NLO EW cross sections and (2) the comparison of those cross sections with LHC data from Run 1, and projections for future measurements in Run 2.
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| 14. |
- Cepeda, M., et al.
(författare)
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Higgs Physics at the HL-LHC and HE-LHC
- 2019
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Ingår i: Report from Working Group 2 on the Physics of the HL-LHC, and Perspectives at the HE-LHC, 364 pages.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 15. |
- Christiansen, Jesper Roy, et al.
(författare)
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Merging weak and QCD showers with matrix elements
- 2016
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 76:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a consistent way of combining associated weak boson radiation in hard dijet events with hard QCD radiation in Drell-Yan-like scatterings. This integrates multiple tree-level calculations with vastly different cross sections, QCD- and electroweak parton-shower resummation into a single framework. The new merging strategy is implemented in the PYTHIA event generator and predictions are confronted with LHC data. Improvements over the previous strategy are observed. Results of the new electroweak-improved merging at a future 100 TeV proton collider are also investigated.
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| 16. |
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| 17. |
- Gellersen, Leif, et al.
(författare)
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Coloring mixed QCD/QED evolution
- 2022
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Ingår i: SciPost Physics. - 2542-4653. ; 13:2
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Tidskriftsartikel (refereegranskat)abstract
- Parton showers are crucial components of high-energy physics calculations. Improving their modelling of QCD is an active research area since shower approximations are stumbling blocks for precision event generators. Naively, the interference between subdominant Standard-Model interactions and QCD can be of similar size to subleading QCD corrections. This article assesses the impact of QCD/QED interference effects in parton showers, by developing a sophisticated shower including QED, QCD at fixed color, and employing complete tree-level matrix element corrections for individual NC = 3 color configurations to embed interference. The resulting simulation indicates that QCD/QED interference effects are small for a simple test case and dwarfed by electro-weak resonance effects.
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| 18. |
- Gellersen, Leif, et al.
(författare)
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Scale and scheme variations in unitarized NLO merging
- 2020
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Ingår i: Physical Review D. - 2470-0010. ; 101:11
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Tidskriftsartikel (refereegranskat)abstract
- Precision background predictions with well-defined uncertainty estimates are important for interpreting collider-physics measurements and for planning future high-energy collider experiments. It is especially important to estimate the perturbative uncertainties in predictions of inclusive measurements of jet observables, that are designed to be largely insensitive to non-perturbative effects such as the structure of beam remnants, multiparton scattering, or hadronization. In this study, we discuss possible pitfalls in defining the perturbative uncertainty of unitarized next-to-leading order (NLO) multijet merged predictions, using the pythia event generator as our vehicle. For this purpose, we consider different choices of unitarized NLO merging schemes as well as consistent variations of renormalization scales in different parts of the calculation. Such a combined discussion allows to rank the contribution of scale variations to the error budget in comparison to other contributions due to algorithmic choices that are often assumed fixed. The scale uncertainty bands of different merging schemes largely overlap, but differences between the "central" predictions in different schemes can remain comparable to scale uncertainties even for very well-separated jets, or be larger than scale uncertainties in transition regions between calculations of different jet multiplicity. The availability of these variations within pythia will enable more systematic studies of perturbative uncertainties in precision background calculations in the future.
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| 19. |
- Gustafson, Gösta, et al.
(författare)
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Collider events on a quantum computer
- 2022
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2022:11
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Tidskriftsartikel (refereegranskat)abstract
- High-quality simulated data is crucial for particle physics discoveries. Therefore, parton shower algorithms are a major building block of the data synthesis in event generator programs. However, the core algorithms used to generate parton showers have barely changed since the 1980s. With quantum computers’ rapid and continuous development, dedicated algorithms are required to exploit the potential that quantum computers provide to address problems in high-energy physics. This paper presents a novel approach to synthesising parton showers using the Discrete QCD method. The algorithm benefits from an elegant quantum walk implementation which can be embedded into the classical toolchain. We use the ibm_algiers device to sample parton shower configurations and generate data that we compare against measurements taken at the ALEPH, DELPHI and OPAL experiments. This is the first time a Noisy Intermediate-Scale Quantum (NISQ) device has been used to simulate realistic high-energy particle collision events.
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| 20. |
- Isaacson, Joshua, et al.
(författare)
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Stochastically sampling color configurations
- 2019
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Ingår i: Physical Review D. - 2470-0010. ; 99:1
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Tidskriftsartikel (refereegranskat)abstract
- Parton shower algorithms are key components of theoretical predictions for high-energy collider physics. Work toward more accurate parton shower algorithms is thus pursued along many different avenues. The systematic treatment of subleading color corrections in parton shower algorithms is, however, technically challenging and remains elusive. In this article, we present an efficient and numerically stable algorithm to sample color configurations at fixed NC=3, using the correct color factor including subleading corrections with a parton shower. The algorithm is implemented as stand-alone program that can be interfaced to the Pythia event generator. Preliminary comparisons to Large Electron-Positron Collider data are presented.
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| 21. |
- Lönnblad, Leif, et al.
(författare)
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Matching tree-level matrix elements with interleaved showers
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- We present an implementation of the so-called CKKW-L merging scheme for combining multi-jet tree-level matrix elements with parton showers. The implementation uses the transverse-momentum-ordered shower with interleaved multiple interactions as implemented in PYTHIA8. We validate our procedure using e(+)e(-)-annihilation into jets and vector boson production in hadronic collisions, with special attention to details in the algorithm which are formally sub-leading in character, but may have visible effects in some observables. We find substantial merging scale dependencies induced by the enforced rapidity ordering in the default PYTHIA8 shower. If this rapidity ordering is removed the merging scale dependence is almost negligible. We then also find that the shower does a surprisingly good job of describing the hardness of multi-jet events, as long as the hardest couple of jets are given by the matrix elements. The effects of using interleaved multiple interactions as compared to more simplistic ways of adding underlying-event effects in vector boson production are shown to be negligible except in a few sensitive observables. To illustrate the generality of our implementation, we also give some example results from di-boson production and pure QCD jet production in hadronic collisions.
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| 22. |
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| 23. |
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| 24. |
- Prestel, Stefan, et al.
(författare)
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HYTREES : combining matrix elements and parton shower for hypothesis testing
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:7
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Tidskriftsartikel (refereegranskat)abstract
- We present a new way of performing hypothesis tests on scattering data, by means of a perturbatively calculable classifier. This classifier exploits the “history tree” of how the measured data point might have evolved out of any simpler (reconstructed) points along classical paths, while explicitly keeping quantum–mechanical interference effects by copiously employing complete leading-order matrix elements. This approach extends the standard Matrix Element Method to an arbitrary number of final state objects and to exclusive final states where reconstructed objects can be collinear or soft. We have implemented this method into the standalone package hytrees and have applied it to Higgs boson production in association with two jets, with subsequent decay into photons. hytrees allows to construct an optimal classifier to discriminate this process from large Standard Model backgrounds. It further allows to find the most sensitive kinematic regions that contribute to the classification.
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| 25. |
- Prestel, Stefan
(författare)
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Improving Parton Showers with Fixed Order Matrix Elements
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis considers numerical simulations of high energy particle collisions, and improvements in the description of multiple collimated jets of hadrons in collision events in particular. In the event simulation software called event generators, the structure of multi-jet events is determined through an interplay of the input calculation, parton showers and phenomenological hadronisation models. Prescriptions to imbue existing event generator simulations with more complex input calculations are presented, and public implementations of the proposed methods provided. Paper I describes the implementation of an earlier algorithm to include regularised tree-level multi-jet configurations into event generators. The implementation is applied to collisions at LEP, Tevatron and LHC. Paper II proposes a method to amend cross section changes in traditional multi-jet merging schemes. The implementation of the new scheme is tested for W-boson + jets and QCD Dijet production at the LHC. Paper III presents extensions of the algorithms of Papers I and II to allow the inclusion of virtual orrections to the scattering processes. The resulting NLO merging methods are applied to W-boson + jets and Higgs-boson + jets at the LHC.
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| 26. |
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| 27. |
- Prestel, Stefan
(författare)
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Matching N3LO QCD calculations to parton showers
- 2021
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2021:11
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Tidskriftsartikel (refereegranskat)abstract
- The search for new interactions and particles in high-energy collider physics relies on precise background predictions. This has led to many advances in combining precise fixed-order cross-section calculations with detailed event generator simulations. In recent years, fixed-order qcd calculations of inclusive cross sections at n3lo precision have emerged, followed by an impressive progress at producing differential results. Once differential results become publicly available, it would be prudent to embed these into event generators to allow the community to leverage these advances. This note offers some concrete thoughts on me+ps matching at third order in qcd. As a method for testing these thoughts, a toy calculation of e+e− → uu¯ at O(αs3) is constructed, and combined with an event generator through unitary matching. The toy implementation may serve also as blueprint for high-precision qcd predictions at future lepton colliders. As a byproduct of the n3lo matching formula, a new nnlo+ps formula for processes with “additional” jets is obtained.
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