PROGRAM SUMMARY
Title of program:
WPHACT, version 2.0
Catalogue identifier:
ADQW
Ref. in CPC:
150(2003)166
Distribution format: tar gzip file
Operating system: UNIX, LINUX, VMS
High speed store required:
500K words
Number of bits in a word:
32
Number of lines in distributed program, including test data, etc:
111387
Keywords:
Elementary Particle physics, Event simulation, High energy electron
Positron collisions, Four-fermion final state, W-pair production,
Higgs, Z-pair production, LEP2, NLC, Corrections QED,
Electron structure, Functions, Coulomb corrections,
Anomalous couplings, Massive matrix elements, Gauge invariance,
Fermion loop, Single W, Single Z, Running alphaQED, CKM mixing,
Resonances.
Programming language used: Fortran
Computer:
Compaq ALPHA workstation,
HP workstation ,
Linux Intel PC .
Other versions of this program:
Cat. Id. Title Ref. in CPC ADEN WPHACT 99(1997)270
Nature of physical problem:
All e+e- Standard Model (SM) processes with four fermion final states
are necessary for detailed studies of the properties of the W and of the
Higgs bosons, for measuring double and single boson production, for high
precision tests of the SM and for evaluating backgrounds to searches.
One wants therefore a Monte Carlo event generator which provides an
accurate description of all four fermion processes in the largest
possible region of phase space and which can be used for realistic
experimental simulations.
Method of solution:
Full tree level matrix elements for all processes are computed by means
of subroutines which make use of the helicity formalism of ref. [1]-[2].
The speed in computing these amplitudes, that the above mentioned method
allows, is essential to take exactly into account fermion masses and to
obtain high precision in a reasonable amount of CPU time also in regions
with large and possibly overlapping enhancements.
Reasons for the new version:
Extend the code to cover in a reliable way all t-channel dominated
processes and low ffbar invariant mass regions. Introduce the
possibility to simultaneously generate unweighted events for all
processes or any user-selected subset. Include photon pt and CKM
mixing.
Summary of revisions:
Fully massive matrix elements, new unweighted event generation for any
subset of four fermion final states in a single run, implementation of
the Imaginary Fermion Loop gauge restoring scheme, new phase space
mappings, new input system, possibility to compute subsets of Feynman
diagrams and options for including ISR via QEDPS, running alphaQED, CKM
mixing, resonances in qqbar channels.
Restrictions:
QED radiative corrections are implemented only in Initial State
Radiation and in Coulomb corrections. Final state radiation is not
computed when unweighted events are not requested. Only the imaginary
part of Fermion Loop corrections is implemented. QCD corrections are
introduced in an approximate way.
Typical running time:
The running time strongly depends on the process considered and on the
precision requested. The example reported in the test run took about 90
minutes on a 500 MHz ALPHA computer, which corresponds to effectively
generating more than 1500 weighted e-e+mu-mu+ events per second.
Unusual features:
STRUCTURE declarations are used.
Additional comments:
Computer: Any computer with FORTRAN77 compiler which admits
structures. WPHACT has been tested on Compaq ALPHA and HP stations as
well as on Linux Intel PC. For this last type of machine the Portland
Group pgf77 compiler has been employed, while the GNU compiler cannot be
used as it does not have the STRUCTURE extension. Compaq and Portland
Group FORTRAN90 compilers can also be used.
References:
[1] A. Ballestrero and E. Maina, Phys. Lett. B350 (1995) 225
[hep-ph/9403244].
[2] A. Ballestrero, 'PHACT 1.0 - Program for Helicity Amplitudes
Calculations with Tau matrices [hep-ph/9911318] in 'Proceedings of
the 14th International Workshop on High Energy Physics and Quantum
Field Theory (QFTHEP 99)', B.B. Levchenko and V.I. Savrin eds.
(SINP MSU Moscow), pg.303.