Matching tree-level matrix elements with interleaved showers

By L. Lonnblad, Stefan Prestel. 2011

269 citations recorded by the source corpus.

A bstractWe 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.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/73c804065903739f9283a83698439cfb9e44be61

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In Nuclear and High Energy Physics

Citations in the corpus

QCD matrix elements + parton showers. The NLO case (2012, methodology): “Either one chooses to veto matrix element configurations where the boundary between matrix element and parton shower regions would be crossed multiple times and fills these regions entirely with the parton shower [32,37].”
Search for electroweak production of supersymmetric particles in final states with two or three leptons at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\odd (2018, methodology): “following the CKKW-L prescription [62], with a matching”
NLO QCD matrix elements + parton showers in e+e− → hadrons (2012, background): “They were pioneered in [1–4] and further matured in [5–8].”
Search for dark matter and other new phenomena in events with an energetic jet and large missing transverse momentum using the ATLAS detector (2017, methodology): “Pythia is performed following the CKKW-L prescription [51].”
Event generation with Sherpa 2.2 (2019, methodology): “resummation in both regions. Originally these ideas have been proposed for the combination of tree-level matrix elements in [26, 27], and have been implemented, in variations, in all event generators [124, 125, 126, 127, 28, 128, 129, 29, 130, 131]. A dedicated comparison can, for example, be found ”
Search for electroweak production of supersymmetric states in scenarios with compressed mass spectra at √s = 13 TeV with the ATLAS detector (2017, unknown): “The ME-PS matching was performed using the CKKW-L scheme [65] with the merging scale set to 15 GeV.”
Soft triple-real radiation for Higgs production at N3LO (2013, unknown): “[15–35] See, for example, refs.”
The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations (2014, methodology): “There are two merging schemes that can be used in conjunction with Pythia6 and Pythia8; in the case of the latter, one is also given the possibility of considering CKKWL approaches [145–147] (after having generated the samples relevant to various parton multiplicities with MadGraph5 aMC@NLO); in wha”