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.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
M.L. Mangano, M. Moretti, F. Piccinini, R. Pittau and A.D. Polosa, ALPGEN, a generator for hard multiparton processes in hadronic collisions, JHEP 07 (2003) 001 [hep-ph/0206293] [INSPIRE].
M. Mangano, The so-called MLM prescription for ME/PS matching, talk presented at the Fermilab ME/MC Tuning Workshop, Batavia U.S.A., October 4, 2002, http://www-cpd.fnal.gov/personal/mrenna/tuning/nov2002/mlm.pdf.
F. Maltoni and T. Stelzer, MadEvent: automatic event generation with MadGraph, JHEP 02 (2003) 027 [hep-ph/0208156] [INSPIRE].
S. Mrenna and P. Richardson, Matching matrix elements and parton showers with HERWIG and PYTHIA, JHEP 05 (2004) 040 [hep-ph/0312274] [INSPIRE].
N. Lavesson and L. Lönnblad, Merging parton showers and matrix elements: back to basics, JHEP 04 (2008) 085 [arXiv:0712.2966] [INSPIRE].
J. Alwall et al., Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions, Eur. Phys. J. C 53 (2008) 473 [arXiv:0706.2569] [INSPIRE].
S. Catani, F. Krauss, R. Kuhn and B.R. Webber, QCD matrix elements + parton showers, JHEP 11 (2001) 063 [hep-ph/0109231] [INSPIRE].
L. Lönnblad, Correcting the color dipole cascade model with fixed order matrix elements, JHEP 05 (2002) 046 [hep-ph/0112284] [INSPIRE].
L. Lönnblad, ARIADNE version 4: a program for simulation of QCD cascades implementing the color dipole model, Comput. Phys. Commun. 71 (1992) 15 [INSPIRE].
F. Krauss, Matrix elements and parton showers in hadronic interactions, JHEP 08 (2002) 015 [hep-ph/0205283] [INSPIRE].
N. Lavesson and L. Lönnblad, W+ jets matrix elements and the dipole cascade, JHEP 07 (2005) 054 [hep-ph/0503293] [INSPIRE].
P. Nason, A new method for combining NLO QCD with shower Monte Carlo algorithms, JHEP 11 (2004) 040 [hep-ph/0409146] [INSPIRE].
T. Sjöstrand, S. Mrenna and P.Z. Skands, A brief introduction to PYTHIA 8.1, Comput. Phys. Commun. 178 (2008) 852 [arXiv:0710.3820] [INSPIRE].
J. Tully Monte Carlo simulations of hard QCD radiation, Ph.D. Thesis, Durham University, Durham U.K. (2009).
T. Gleisberg et al., Event generation with SHERPA 1.1, JHEP 02 (2009) 007 [arXiv:0811.4622] [INSPIRE].
J. Alwall et al., A standard format for Les Houches event files, Comput. Phys. Commun. 176 (2007) 300 [hep-ph/0609017] [INSPIRE].
M. Cacciari and G.P. Salam, Dispelling the N 3 myth for the k t jet-finder, Phys. Lett. B 641 (2006) 57 [hep-ph/0512210] [INSPIRE].
K. Hamilton and P. Nason, Improving NLO-parton shower matched simulations with higher order matrix elements, JHEP 06 (2010) 039 [arXiv:1004.1764] [INSPIRE].
S. Höche, F. Krauss, M. Schönherr and F. Siegert, NLO matrix elements and truncated showers, JHEP 08 (2011) 123 [arXiv:1009.1127] [INSPIRE].
R. Corke and T. Sjöstrand, Interleaved parton showers and tuning prospects, JHEP 03 (2011) 032 [arXiv:1011.1759] [INSPIRE].
S. Höche, F. Krauss, S. Schumann and F. Siegert, QCD matrix elements and truncated showers, JHEP 05 (2009) 053 [arXiv:0903.1219] [INSPIRE].
J.R. Andersen and J.M. Smillie, Multiple jets at the LHC with high energy jets, JHEP 06 (2011) 010 [arXiv:1101.5394] [INSPIRE].
OPAL collaboration, G. Abbiendi et al., A simultaneous measurement of the QCD color factors and the strong coupling, Eur. Phys. J. C 20 (2001) 601 [hep-ex/0101044] [INSPIRE].
A. Buckley et al., Rivet user manual, arXiv:1003.0694 [INSPIRE].
ATLAS collaboration, G. Aad et al., Measurement of the production cross section for W-bosons in association with jets in pp collisions at \( \sqrt {s} \) = 7 TeV with the ATLAS detector, Phys. Lett. B 698 (2011) 325 [arXiv:1012.5382] [INSPIRE].
CDF collaboration, T. Aaltonen et al., Measurement of inclusive jet cross-sections in Z/γ *(→ e + e −) + jets production in \( p\overline p \) collisions at \( \sqrt {s} \) = 1.96 TeV, Phys. Rev. Lett. 100 (2008) 102001 [arXiv:0711.3717] [INSPIRE].
The CDF collaboration, T. Aaltonen et al., Studying the underlying event in Drell-Yan and high transverse momentum jet production at the Tevatron, Phys. Rev. D 82 (2010) 034001 [arXiv:1003.3146] [INSPIRE].
CDF collaboration, T. Aaltonen et al., Invariant mass distribution of jet pairs produced in association with a W boson in \( p\overline p \) collisions at \( \sqrt {s} \) = 1.96 TeV, Phys. Rev. Lett. 106 (2011) 171801 [arXiv:1104.0699] [INSPIRE].
G.C. Blazey et al., Run II jet physics, hep-ex/0005012 [INSPIRE].
CDF collaboration, D. Acosta et al., Study of jet shapes in inclusive jet production in \( p\overline p \) collisions at \( \sqrt {s} \) = 1.96 TeV, Phys. Rev. D 71 (2005) 112002 [hep-ex/0505013] [INSPIRE].
S. Frixione, P. Nason and C. Oleari, Matching NLO QCD computations with Parton Shower simulations: the POWHEG method, JHEP 11 (2007) 070 [arXiv:0709.2092] [INSPIRE].
Author information
Authors and Affiliations
Corresponding author
Additional information
ArXiv ePrint: 1109.4829
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License ( https://creativecommons.org/licenses/by/2.0 ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
About this article
Cite this article
Lönnblad, L., Prestel, S. Matching tree-level matrix elements with interleaved showers. J. High Energ. Phys. 2012, 19 (2012). https://doi.org/10.1007/JHEP03(2012)019
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1007/JHEP03(2012)019