HELAC-PHEGAS

Monte Carlo Event Generator for All Parton Level Processes


Project Description


HELAC is a multi-purpose, tree-level  event generator which is the only existing implementation of the algorithm based on Dyson-Schwinger equations. It can be used to efficiently obtain helicity amplitudes and total cross sections  for arbitrary multiparticle processes in the Standard Model. The program can generate all processes with 10 or more final state particles with full off-shell and finite width effects taking into account naturally both, spin and color correlations. All electroweak vertices in both Feynman and unitary gauges have been included. The program incorporates the possibility to use extended numerical precision. It is also possible to get numerical predictions for amplitudes for arbitrary processes for phase-space points provided by the user.

For the phase space generation the PHEGAS program is used which has been the first implementation of a complete automated algorithm of multi-channel phase-space mappings for arbitrary number of external particles. It also uses a self-adaptation procedure that reshapes the generated phase-space density, including also the PARNI  algorithm for the efficient integration over parton distribution functions.
The program generates parton-level events with all necessary information, in the most recent Les Houches Accord format, for the study of any process at hadron and lepton colliders. Moreover, the emission of secondary partons  as well as the translation of the emerging partons into primordial hadrons is performed by interfacing HELAC-PHEGAS to PYTHIA.  In addition, the so called MLM matching procedure is used to combine fixed order tree level matrix element calculations with parton showers in order to avoid double counting of jet configurations.

The program has been built with future extensions in mind. The design includes all mechanisms for expanding the program with new capabilities without having to make major changes to the main structure. Because of this it is straightforward to add new physics effects by including new models and new couplings. Moreover, a tested upgrade with high color charge processes treated via Monte Carlo summation over color is available.

The code is written in Fortran 95 and has been developed using the following compilers under Linux: Lahey Fujitsu, Intel Fortran, GNU gfortran and g95. The stand-alone codes do not need any external library. However, LHAPDF is supported as an option.

The use of the code is very easy. The user has just to run a shell script that produces the file with the un-weighted events in the Les Houches format. Parameters, like physical constants, number of un-weighted events or phase-space cuts can be entered, in a very transparent way, in the user.inp file. Default values for all of them exist in the default.inp file. The script also supports running under the LSF batch system, so that each sub-process runs on a different computer on the LSF cluster and it automatically collects all information, without any intervention from the user. It has been successfully tested at lxplus at CERN.

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Dipoles


   DIPOLES   

Package includes the massless dipole formalism of  Catani and Seymour,  as well as its massive version as developed by Catani, Dittmaier, Seymour and Trocsanyi, for arbitrary helicity eigenstates of the external partons.

! Integrated dipoles implemented for massless and massive cases  !

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Project Members

Costas G. Papadopoulos   
Malgorzata Worek    
Michal Czakon  (Dipoles Package)

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Compilers:

    gfortran
    g95
    lahey 95
    Intel Fortran

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Software Download

   
   DIPOLES  Version 1.1.0 (27 July 2009):  dipoles.tgz
                    the README file contains installation and usage instructions
                    HELAC-PHEGAS + DIPOLES:  preconfigured.tgz
                    Preconfigured version to reproduce the results from the paper

   HELAC-PHEGAS  Version 1.2.0 (6 May 2009):  helac-phegas.1.2.0.tar.gz

Version 1.1.0 (18 January 2008):  tar file    

Version 1.0.0 (17 October 2007):  tar file

Version 0.1.0 (24 July 2006):  tar file

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Manual & References

 
HELAC-PHEGAS Manual

The following papers should be cited while using HELAC-PHEGAS package

Helac-Phegas: A Generator for all parton level processes
A. Cafarella, C. G. Papadopoulos, M. Worek
arXiv:0710.2427 [hep-ph]

PHEGAS: A Phase space generator for automatic cross-section computation
C. G. Papadopoulos
Comput. Phys. Commun. 137 (2001) 247

HELAC: A Package to compute electroweak helicity amplitudes
A. Kanaki, C. G. Papadopoulos
Comput. Phys. Commun. 132 (2000) 306


The following paper should be cited while using DIPOLES package

Polarizing the Dipoles
M. Czakon, C. G. Papadopoulos and M. Worek
 arXiv:0905.0883 [hep-ph]

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News & Developments & Bug Report


Changes in HELAC-DIPOLES Version 1.1.0

     Integrated dipoles implemented for massless and massive cases
     Phase space restriction dependence included in the massless and massive cases
     A bug in the jet function fixed
     Phase space integrator corrected

Changes in HELAC-PHEGAS Version 1.2.0

     lhaglue.f file has been removed from the package to allow HELAC to run with the newest
        LHAPDF lhaglue interface within the lhapdf-5.7.0 version.   
     Several bugs fixed
     New version of PARNI included
  
Changes in HELAC-PHEGAS Version 1.1.0

     Scripts have been added and some files have been modified to allow running HELAC with
        the LSF system.
     A bug in main_mc.f has been fixed.
     Shell changed from sh to bash.
     "special" directory added to allow removal of some vertices in particular situations.
     Many unnecessary files have been removed.
     README file has been updated.
     Some minor changes in the output format.

Validation

     u ubar ->  t tbar 
     p p ->  W + 1 jet

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Contact us


If you have a question, comment, suggestion or bug report, please e-mail us at:

Costas.Papadopoulos(at)cern.ch  
Malgorzata.Worek(at)cern.ch 
mczakon(at)physik.uni-wuppertal.de  (Dipoles Package)

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Last modified by Malgorzata Worek  Mon July 27,  2009