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[Licence| Download | New Version Template] adqq_v2_0.tar.gz(66450 Kbytes)
Manuscript Title: The Monte Carlo Event Generator AcerMC versions 2.0 to 3.8 with interfaces to PYTHIA 6.4, HERWIG 6.5 and ARIADNE 4.1
Authors: Borut Paul Kersevan, Elzbieta Richter-Was
Program title: AcerMC version 3.8
Catalogue identifier: ADQQ_v2_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 184(2013)919
Programming language: FORTRAN 77 with popular extensions (g77, gfortran).
Computer: All running Linux.
Operating system: Linux.
Keywords: Standard Model backgrounds at LHC, Massive matrix elements, Monte Carlo generator, Heavy flavor production, Multi-channel phase-space generation.
PACS: 13.90.+i.
Classification: 11.2, 11.6.

External routines: CERNLIB (http://cernlib.web.cern.ch/cernlib/), LHAPDF (http://lhapdf.hepforge.org/)

Does the new version supersede the previous version?: Yes

Nature of problem:
Despite a large repertoire of processes implemented for generation in event generators like PYTHIA [1] or HERWIG [2] a number of background processes, crucial for studying the expected physics of the LHC experiments, is missing. For some of these processes the matrix element expressions are rather lengthly and/or to achieve a reasonable generation efficiency it is necessary to tailor the phasespace selection procedure to the dynamics of the process. That is why it is not practical to imagine that any of the above general purpose generators will contain every, or even only observable, processes which will occur at LHC collisions. A more practical solution can be found in a library of dedicated matrix-element-based generators, with the standardised interfaces like that proposed in [3], to the more universal one which is used to complete the event generation.

Solution method:
The AcerMC EventGenerator provides a library of the matrix-element-based generators for several processes. The initial- and final- state showers, beam remnants and underlying events, fragmentation and remaining decays are supposed to be performed by the other universal generator to which this one is interfaced. We will call it supervising generator. The interfaces to PYTHIA 6.4, ARIADNE 4.1 and HERWIG 6.5, as such generators, are provided. Provided is also an interface to TAUOLA [4] and PHOTOS [5] packages for τ-lepton decays (including spin correlations treatement) and QED radiations in decays of particles. At present, the following matrix-element-based processes have been implemented: gg, qqbar → ttbarbbbar, qqbar → W(→ lv)bbbar; qqbar → W(→ lv)ttbar; gg, qqbar → Z/γ*(→ ll)bbbar; gg, qqbar → Z/γ*(→ ll, vv, bb)tt; complete EW gg, qqbar → (Z/W/γ* →)ttbb; gg, qqbar → ttbarttbar; gg, qqbar → (ttbar →)ffbarbffbarbbar; gg,qqbar → (WWbb →) ffffbb. Both interfaces allow the use of the LHAPDF/LHAGLUE library of parton density functions. Provided is also a set of control processes: qqbar → W → lv; qqbar → Z/γ* → ll; gg, qqbar → ttbar and gg → (ttbar →)WbWbbar.

Reasons for new version:
Implementation of several new processes and methods.

Summary of revisions:
Each version added new processes or functionalities, a detailed list is given in the section "Changes since AcerMC 1.0".

The package is optimized for the 14 TeV pp collision simulated in the LHC environment and also works at the achieved LHC energies of 7 TeV and 8 TeV. The consistency between results of the complete generation using PYTHIA 6.4 or HERWIG 6.5 interfaces is technically limited by the different approaches taken in both these generators for evaluating αQCD and αQED couplings and by the different models for fragmentation/hadronisation. For the consistency check, in the AcerMC library contains native coded definitions of the QCD and αQED. Using these native definitions leads to the same total cross-sections both with PYTHIA 6.4 or HERWIG 6.5 interfaces.

Running time:
On an PIII 800 MHz PC it amounts to ~ 0.05 → 1.1 events/sec, depending on the choice of process.

[1] T. Sjostrand et al., High energy physics generation with PYTHIA 6.2, eprint hep-ph/0108264, LU-TP 01-21, August 2001.
[2] G. Julyesini et al., Comp. Phys. Commun. 67 (1992) 465, G. Corcella et al., JHEP 0101 (2001) 010.
[3] E. Boos at al., Generic user process interface for event generators, hepph /0109068.
[4] S. Jadach, J. H. Kuhn, Z. Was, Comput. Phys. Commun. 64 (1990) 275; M. Jezabek, Z. Was, S. Jadach, J. H. Kuhn, Comput. Phys. Commun. 70 (1992) 69; R. Decker, S. Jadach, J. H. Kuhn, Z. Was, Comput. Phys. Commun. 76 (1993) 361.
[5] E. Barberio and Z. Was, Comp. Phys. Commun. 79 (1994) 291.