1,720,984 research outputs found
Introducing MCgrid 2.0: Projecting cross section calculations on grids
No full textMCgrid is a software package that provides access to interpolation tools for Monte Carlo event generator codes, allowing for the fast and flexible variation of scales, coupling parameters and PDFs in cutting edge leading- and next-to-leading-order QCD calculations. We present the upgrade to version 2.0 which has a broader scope of. interfaced interpolation tools, now providing access to fastNLO, and features an approximated treatment for the projection of MC@NLO-type calculations onto interpolation grids. MCgrid 2.0 also now supports the extended information provided through the HepMC event record used in the recent SHERPA version 2.2.0. The additional information provided therein allows for the support of multi-jet merged QCD calculations in a future update of MCgrid. New version program summary Program title: MCgrid Catalogue identifier: AESS_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AESS_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 512334 No. of bytes in distributed program, including test data, etc.: 4263504 Distribution format: tar.gz Programming language: C++, shell, Python. Computer: PC running Linux, Mac. Operating system: Linux, Mac OS. RAM: Varying Catalogue identifier of previous version: AESS_v1_0 Journal reference of previous version: Comput. Phys. Comm. 185(2014)2115 Classification: 11.2, 11.5, 11.9. External routines: HepMC [1], Rivet [2], APPLgrid [3] and fastNLO [4]. A SHERPA [5] installation is also required. Does the new version supersede the previous version?: Yes Nature of problem: Efficient filling of cross section grid files from fully exclusive parton level Monte Carlo events. Solution method: Analyse Monte Carlo events via the Rivet program, which projects events on discretized cross section tables from APPLgrid [3] or fastNLO [4]. Reasons for new version: Previous MCgrid releases, cf. [6], supported only a single interpolation tool: APPLgrid [3]. Interfacing to more than one is important for cross checks and allows the use of MCgrid in a wider range of existing workflows. The recently released SHERPA 2.2.0 provides more information in the HepMC [1] event record, allowing for the filling of the exact next-to-leading-order expansion of an MC@NLO calculation, see e.g. [7] for details, into an interpolation grid. To process the additional information and adopt the new weight naming convention used in SHERPA 2.2.0, modifications on the MCgrid side have been necessary. The possibility of filling grids for MC@NLO-type calculations broadens the scope of MCgrid. It allows for the quantification of the residual dependencies on the parton showers that are beyond the fixed-order approximation. Understanding these dependencies and eventually taking them into account during the creation of interpolation grids in an automated way would help in the fitting of PDFs to data that are not appropriately described by fixed-order calculations. Summary of revisions: As an additional interpolation tool fastNLO [4] is now supported. This is the first time the fastNLO package can be used in conjunction with a multi-purpose Monte Carlo event generator. The required version of the fastNLO toolkit [8] is 2.3.1pre-2125 or later. With APPLgrid and fastNLO, all currently available interpolation tools for fixed-order QCD cross sections can now be used in conjunction with MCgrid. Modifications have been made in order to adopt the new naming conventions in the HepMC event record format introduced in SHERPA 2.2.0. The filling of the exact next-to-leading-order expansion of MC@NLO calculations has been implemented. The required information must be provided with the HepMC event record, which is the case for SHERPA 2.2.0. The MCgrid::BinnedGrid class has been added. It corresponds to the Rivet::BinnedHistogram class and allows for the direct creation of grids for every Rivet histogram combined therein. MCGRID_OUTPUT_PATH has been introduced, an environmental variable for specifying the grid output directory. An automatic counter suffix for grid file names has been added to prevent overwriting. The API has been streamlined for easier enabling of Rivet analyses for MCgrid. The provided examples have been updated for use with SHERPA 2.2.0 and Rivet 2.2.1. Running time: Approximately 6 min per 1 million Drell Yan events from SHERPA. This includes both the event generation and the MCgrid computations. The times can vary quite dramatically. The process used in the test case (which is a relatively quick one) takes about 2 min 30 s for the initial (phase-space fill) run and about 3 min for the second and final run. This is for 1 million events on a 2.9GhZ Ivy Bridge i7 processor. (C) 2015 Elsevier B.V. All rights reserved
Automated evaluation of electroweak Sudakov logarithms in
No full textWe present an automated implementation for the calculation of one-loop double and single Sudakov logarithms stemming from electroweak radiative corrections within the SHERP
Algorithms for numerically stable scattering amplitudes
No full textThe numerically stable evaluation of scattering matrix elements near the infrared limit of gauge theories is of great importance for the success of collider physics experiments. We present a novel algorithm that utilizes double-precision arithmetic and reaches higher precision than a naive quadruple-precision implementation at smaller computational cost. The method is based on physics-driven modifications to propagators, vertices, and external polarizations. Published by the American Physical Society 2024Fermilab http://dx.doi.org/10.13039/100006230U.S. Department of Energy http://dx.doi.org/10.13039/100000015Office of Science http://dx.doi.org/10.13039/100006132High Energy Physics http://dx.doi.org/10.13039/100006208Office of Advanced Scientific Computing Research http://dx.doi.org/10.13039/100006192Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659National Energy Research Scientific Computing Center http://dx.doi.org/10.13039/100017223Scientific Discovery through Advanced Computin
Reweighting QCD matrix-element and parton-shower calculations
Full text linkWe present the implementation and validation of the techniques used to efficiently evaluate parametric and perturbative theoretical uncertainties in matrix-element plus parton-shower simulations within the Sherpa event-generator framework. By tracing the full αsαs and PDF dependences, including the parton-shower component, as well as the fixed-order scale uncertainties, we compute variational event weights on-the-fly, thereby greatly reducing the computational costs to obtain theoretical-uncertainty estimates
Exploring phase space with Neural Importance Sampling
No full textWe present a novel approach for the integration of scattering cross sections and the generation of partonic event samples in high-energy physics. We propose an importance sampling technique capable of overcoming typical deficiencies of existing approaches by incorporating neural networks. The method guarantees full phase space coverage and the exact reproduction of the desired target distribution, in our case given by the squared transition matrix element. We study the performance of the algorithm for a few representative examples, including top-quark pair production and gluon scattering into three- and four-gluon final states
Many-gluon tree amplitudes on modern GPUs: A case study for novel event generators
No full textThe compute efficiency of Monte-Carlo event generators for the Large Hadron Collider is expected to become a major bottleneck for simulations in the high-luminosity phase. Aiming at the development of a full-fledged generator for modern GPUs, we study the performance of various recursive strategies to compute multi-gluon tree-level amplitudes. We investigate the scaling of the algorithms on both CPU and GPU hardware. Finally, we provide practical recommendations as well as baseline implementations for the development of future simulation programs. The GPU implementations can be found at: https://www.gitlab.com/ebothmann/blockgen-archive
A Portable Parton-Level Event Generator for the High-Luminosity LHC
Full text linkThe rapid deployment of computing hardware different from the traditional CPU+RAM model in data centers around the world mandates a change in the design of event generators for the Large Hadron Collider, in order to provide economically and ecologically sustainable simulations for the high-luminosity era of the LHC. Parton-level event generation is one of the most computationally demanding parts of the simulation and is therefore a prime target for improvements. We present a production-ready leading-order parton-level event generation framework capable of utilizing most modern hardware and discuss its performance in the standard candle processes of vector boson and top-quark pair production with up to five additional jets.Submission to SciPost, 32 pages, 11 figures, 2 tables; this is a new version that contains extended discussions and additional content, in particular the new appendix E on CPU vectorizatio
Aspects of perturbative QCD at a 100 TeV future hadron collider
Full text linkIn this paper we consider particle production at a future circular hadron collider with 100 TeV center-of-mass energy within the Standard Model, and in particular their QCD aspects. Accurate predictions for these processes pose severe theoretical challenges related to large hierarchies of scales and possible large multiplicities of final-state particles. We investigate scaling patterns in multijet-production rates allowing to extrapolate predictions to very high final-state multiplicities. Furthermore, we consider large-area QCD jets and study the expectation for the mean number of subjets to be reconstructed from their constituents and confront these with analytical resummed predictions and with the expectation for boosted hadronic decays of top quarks and W bosons. We also discuss the validity of Higgs effective field theory in making predictions for Higgs-boson production in association with jets. Finally, we consider the case of new physics searches at such a 100 TeV hadron-collider machine and discuss the expectations for corresponding Standard-Model background processes
Higher-order EW corrections in ZZ and ZZj production at the LHC
Full text linkWe consider the production of a pair of bosons at the LHC and study the
inclusion of EW corrections in theoretical predictions at fixed order and based
on multijet-merged parton-shower simulations. To this end we present exact NLO
EW results for , and, for the first time, for , and compare them to the EW virtual and NLL Sudakov
approximation. We then match the exact NLO EW result to the resummed Sudakov
logarithms to achieve an improved NLO EW + NLL
result. Further, we discuss the inclusion of
the above EW corrections in MEPS@NLO event simulations in the framework of the
Sherpa event generator. We present detailed phenomenological predictions for
inclusive and production taking into account the dominant EW
corrections through the EW virtual approximation, as well as through
(exponentiated) EW Sudakov logarithms.Comment: 39 pages, 12 figures, 3 table
Efficient precision simulation of processes with many-jet final states at the LHC
No full textFermilab http://dx.doi.org/10.13039/100006230U.S. Department of Energy http://dx.doi.org/10.13039/100000015Office of Science http://dx.doi.org/10.13039/100006132High Energy Physics http://dx.doi.org/10.13039/100006208Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Science and Technology Facilities Council http://dx.doi.org/10.13039/501100000271SoftWare and InFrastructure Technology for High Energy Physic
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