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[Licence| Download | New Version Template] adms_v2_0.tar.gz(371 Kbytes)
Manuscript Title: HELAC-PHEGAS: a generator for all parton level processes
Authors: Alessandro Cafarella, Costas G. Papadopoulos, Malgorzata Worek
Program title: HELAC-PHEGAS
Catalogue identifier: ADMS_v2_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 180(2009)1941
Programming language: Fortran.
Computer: All.
Operating system: Linux.
Keywords: Dyson-Schwinger equations, recursive algorithms, automatic evaluation of helicity amplitudes and total cross sections.
PACS: 12.38.Bx, 13.85.Dz, 13.85.Lg.
Classification: 11.1, 11.2.

External routines: Optionally Les Houches Accord (LHA) PDF Interface library (http://projects.hepforge.org/lhapdf/)

Does the new version supersede the previous version?: Yes, partly

Nature of problem:
One of the most striking features of final states in current and future colliders is the large number of events with several jets. Being able to predict their features is essential. To achieve this, the calculations need to describe as accurately as possible the full matrix elements or the underlying hard processes. Even at leading order, perturbation theory based on Feynman graphs runs into computational problems, since the number of graphs contributing to the amplitude grows as n!.

Solution method:
Recursive algorithms based on Dyson-Schwinger equations have been developed recently in order to overcome the computational obstacles. The calculation of the amplitude, using Dyson-Schwinger recursive equations, results in a computational cost growing asymptotically as 3n, where n is the number of particles involved in the process. Off-shell subamplitudes are introduced, for which a recursion relation has been obtained allowing to express an n-particle amplitude in terms of subamplitudes, with 1-, 2-, ... up to (n-1) particles. The color connection representation is used in order to treat amplitudes involving colored particles. In the present version HELAC-PHEGAS can be used to efficiently obtain helicity amplitudes, total cross sections, parton-level event samples in LHA format, for arbitrary multiparticle processes in the Standard Model in leptonic, ppbar and pp collisions.

Reasons for new version:
Substantial improvements, major functionality upgrade

Summary of revisions:
Color connection representation, efficient integration over PDF via the PARNI algorithm, interface to LHAPDF, parton level events generated in the most recent LHA format, k⊥ reweighting for Parton Shower matching, numerical predictions for amplitudes for arbitrary processes for phase space points provided by the user, new user interface and the possibility to run over computer clusters.

Running time:
Depending on the process studied. Usually from seconds to hours.

[1] A. Kanaki, C. G. Papadopoulos, Comput. Phys. Commun. 132 (2000) 306
[2] C. G. Papadopoulos, Comput. Phys. Commun. 137 (2001) 247