QCD matrix elements and truncated showers

By Stefan Hoeche, F. Krauss, Steffen Schumann, F. Siegert. 2009

723 citations recorded by the source corpus.

We derive an improved prescription for the merging of matrix elements with parton showers, extending the CKKW approach. A flavour-dependent phase space separation criterion is proposed. We show that this new method preserves the logarithmic accuracy of the shower, and that the original proposal can be derived from it. One of the main requirements for the method is a truncated shower algorithm. We outline the corresponding Monte Carlo procedures and apply the new prescription to QCD jet production in ee collisions and DrellYan lepton pair production. Explicit colour information from matrix elements obtained through colour sampling is incorporated in the merging and the influence of different prescriptions to assign colours in the large NC limit is studied. We assess the systematic uncertainties of the new method.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/7326a5b9a7d41515316a592844efaae00f961107

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Citations in the corpus

Mass effects in the Higgs-gluon coupling: boosted vs. off-shell production (2014, methodology): “[85, 86] or, where not otherwise stated at NLO according to the Meps@Nlo algorithm [87, 88].”
Les Houches 2017: Physics at TeV Colliders Standard Model Working Group Report (2017, methodology): “Here, scales are set using the CKKW procedure [924,935].”
General-purpose event generators for LHC physics (2011, methodology): “One of the key features of Sherpa is a generic implementation of the technique for combining tree-level matrix elements with parton showers that was presented in [75], see Section 5.”
Matching tree-level matrix elements with interleaved showers (2011, background): “Provided considerable unitarity violations remain after excluding differences between the full allowed and the PS phase space, this could suggest large higher-order corrections, since by choosing a low merging scale we effectively include major parts of the real emission phase space of an NLO calcul”
NLO QCD matrix elements + parton showers in e+e− → hadrons (2012, methodology): “10) is determined by backward clustering, as described in [5].”
Event generation with Sherpa 2.2 (2019, methodology): “The merging of multi-jet production processes at leading order [26, 27, 28] and next-to-leading order [29, 30] is based on truncated parton showers.”
Measurement of the top quark mass using proton-proton data at √s=7 and 8 TeV (2016, methodology): “0 with up to 4 additional jets from the LO matrix element [57,58]; (v) POWHEG with the PYTHIA Z2* tune [16,21–25,56]; (vi) POWHEG with the HERWIG 6.”
Les Houches 2015: Physics at TeV Colliders Standard Model Working Group Report (2016, methodology): “The n-parton matrix elements are then clustered in the scheme of [244,255,389] to find a suitable core configuration and defining μcore = (1)2 mh for the present study.”
NLO QCD+EW predictions for V + jets including off-shell vector-boson decays and multijet merging (2015, methodology): “For a more detailed discussion of technical aspects we refer to the original publications [54, 55, 92, 96].”
Coherent parton showers with local recoils (2009, neutral): “Recent improvements address previous deficiencies of the CKKW algorithm in filling the phase space [30,31] that had been discussed extensively in [32].”
Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using sqrt(s)=7 TeV pp collisions with the ATLAS detector (2011, neutral): “Elec-troweak and top contributions are obtained from a mixture of control measurements, and JHEP11 ( 2011 ) 099 transfer factors calculated from sophisticated multi-leg Monte Carlo simulations [18–21].”