24 research outputs found
Aspects of QCD uncertainties and fast QCD predictions for high-energy collider experiments
In dieser Arbeit adressieren wir die Schwierigkeit, Präzisionsvorhersagen mit dem kompletten Satz theoretischer Unsicherheiten in der perturbativen Quantenchromodynamik im Rahmen von Monte-Carlo-Simulationen zu treffen, angesichts der zunehmenden Komplexität der dazu nötigen Berechnungen. Die Anforderungen an die Rechenleistung können so groß sein, dass nicht in jeder Anwendung die bestmögliche Präzision erzielt wird.
Wir präsentieren eine Reweighting-Methode für den Monte-Carlo-Ereignisgenerator SHERPA. Diese erstellt Variationen der nominellen Vorhersage mit vergleichsweise geringem zusätzlichen Zeitaufwand. Die Methode ist kompatibel mit aktuellen Multijet-Berechnungen nächsthöherer Ordnung, die mit Korrekturen von allen Ordnungen durch einen Partonschauer versehen sind.
Zusätzlich diskutieren wir neue Entwicklungen für einen weiteren Reweighting-Ansatz, der auf QCD-Interpolationsgittern beruht. Diese ermöglichen noch schnellere Variationen für Berechnungen fester Ordnung. Solche Gitter können für Monte-Carlo-Simulationen automatisiert erstellt werden mithilfe von Interfaces wie MCgrid. Unsere Verbesserungen für MCgrid ermöglichen die Erstellung vielseitigerer Gitter, die eine größere Klasse von Berechnungen, Gitter-Implementierungen und Skalenvariationen unterstützen. Darüber hinaus diskutieren wir, auf welche Weise solche Gitter für die Unterstützung von Resummationseffekten erweitert werden müssten.
Neben dem Reweighting studieren wir noch die Verwendung von Extrapolationsmethoden für die Vorhersage von Jet-Raten hoher Multiplizitäten, welche an zukünftigen Hochenergiebeschleunigern allgegenwärtig sein werden. Diese Methoden basieren auf dem Skalierungsverhalten der Jet-Raten. Eingebettet ist diese Studie in eine allgemeinere Diskussion der zu erwartenden Jet-Aktivität an einem Proton-Proton-Beschleuniger mit einer Schwerpunktsenergie von 100 TeV
Automated evaluation of electroweak Sudakov logarithms in Sherpa
We present an automated implementation for the calculation of one-loop double
and single Sudakov logarithms stemming from electroweak radiative corrections
within the Sherpa event generation framework, based on the derivation in[1]. At
high energies, these logarithms constitute the leading contributions to the
full NLO electroweak corrections. As examples, we show applications for
relevant processes at both the LHC and future hadron colliders, namely on-shell
W boson pair production, EW-induced dijet production and electron-positron
production in association with four jets, providing the first estimate of EW
corrections at this multiplicity.Comment: 17 pages, 4 figure
Single top-quark production with sherpa
We present results at next-to-leading order accuracy in QCD for single top-quark production in the t, s and tW channels at the lhc at a centre-of-mass energy of 8TeV, obtained with the sherpa event generator. We find them in very good agreement with measured values and quantify their theory uncertainties. Uncertainties stemming from the choice between the four- and the five-flavour scheme are found to be typically of the order of 5–10% over large ranges of phase space. We discuss the impact of parton distribution functions, and in particular of the bottom PDF. We also show how different cuts on QCD radiation patterns improve the signal-to-background ratio in realistic fiducial volumes
A Portable Parton-Level Event Generator for the High-Luminosity LHC
Parton-level event generators are one of the most computationally demanding
parts of the simulation chain for the Large Hadron Collider. The rapid
deployment of computing hardware different from the traditional CPU+RAM model
in data centers around the world mandates a change in event generator design.
These changes are required in order to provide economically and ecologically
sustainable simulations for the high-luminosity era of the LHC. We present the
first complete leading-order parton-level event generation framework capable of
utilizing most modern hardware. Furthermore, we discuss its performance in the
standard candle processes of vector boson and top-quark pair production with up
to five additional jets.Comment: Submission to SciPost, 23 pages, 7 figures, 2 table
Efficient precision simulation of processes with many-jet final states at the LHC
We present a scalable technique for the simulation of collider events with
multi-jet final states, based on an improved parton-level event file format.
The method is implemented for both leading- and next-to-leading order QCD
calculations. We perform a comprehensive analysis of the I/O performance and
validate our new framework using Higgs-boson plus multi-jet production with up
to seven jets. We make the resulting code base available for public use.Comment: 14 pages, 7 figures, 2 table
Efficient phase-space generation for hadron collider event simulation
We present a simple yet efficient algorithm for phase-space integration at
hadron colliders. Individual mappings consist of a single t-channel combined
with any number of s-channel decays, and are constructed using diagrammatic
information. The factorial growth in the number of channels is tamed by
providing an option to limit the number of s-channel topologies. We provide a
publicly available, parallelized code in C++ and test its performance in
typical LHC scenarios.Comment: 11 pages, 3 figure
Event Generation with Sherpa 2.2
Sherpa is a general-purpose Monte Carlo event generator for the simulation of particle collisions in high-energy collider experiments. We summarize essential features and improvements of the Sherpa 2.2 release series, which is heavily used for event generation in the analysis and interpretation of LHC Run 1 and Run 2 data. We highlight a decade of developments towards ever higher precision in the simulation of particle-collision events