PROGRAM SUMMARY
Title of program:
AcerMC version 1.0
Catalogue identifier:
ADQQ
Ref. in CPC:
149(2003)142
Distribution format: tar gzip file
Operating system: Linux
Number of lines in distributed program, including test data, etc:
235005
Keywords:
Standard Model backgrounds at LHC, Massive matrix elements,
Monte Carlo generator, Heavy flavor production, Multi-channel
phase space generation, Elementary particle physics.
Programming language used: Fortran
Computer:
PIII 800 MHz PC .
Nature of physical 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 expected physics potential of the LHC
experiments is missing. For some of these processes the matrix element
expressions are rather lengthy and/or to achieve a reasonable generation
efficiency it is necessary to tailor the phase-space 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.
Method of solution:
The AcerMC Event Generator itself provides library of the
matrix-element-based generators for a few example 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 6.2 and HERWIG 6.3,
as such generators, are provided. At present, the following
matrix-element-based processes have been implemented: gg,
qqbar -> ttbarbbbar, qqbar -> W(-> lnu)bbbar; qqbar -> W(->lnu)ttbar,
gg, qqbar -> Z/gamma*(-> ll)bbbar; gg,
qqbar -> Z/gamma*(-> ll, nunu, bbbar)ttbar and complete EW
gg -> (Z/W/gamma* ->)ttbarbbbar. Both interfaces allow the use of the
PDFLIB library of parton density functions.
The program uses CERNLIB library.
Restrictions:
The package is dedicated for the 14 TeV pp collision simulated in the
LHC environment. In particular, using it for the 2 TeV ppbar collision
although technically possible might not be efficient and would require
dedicated optimisation of the phase space generation. The consistency
between results of the complete generation using PYTHIA 6.2 or HERWIG
6.3 interfaces is technically limited by the different approaches taken
in both these generators for evaluating alphaQCD and alphaQED couplings
and by the different models for fragmentation/hadronisation. For the
consistency check, in the AcerMC library contains coded definitions of
the alphaQCD and alphaQED. Using these native definitions leads to the
same total cross-sections both with PYTHIA 6.2 or HERWIG 6.3 interfaces.
Typical running time:
On a PIII 800 MHz PC it amounts to ~0.05 -> 1.1 events/sec, depending on
the choice of process.
References:
[1] T. Sjostrand et al., High energy physics generation with PYTHIA 6.2,
reprint hep-ph/0108264, LU-TP 01-21, August 2001.
[2] G. Marchesini et al., Comp. Phys. Commun. 67 (1992) 465, G. Corcella
et al., JHEP 0101 (2001) 010.
[3] E. Boos et al., Generic user process interface for event generators,
hep-ph/0109068.