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Manuscript Title: WWGENPV 2.0 - A Monte Carlo event generator for four-fermion production at e+e- colliders.
Authors: D.G. Charlton, G. Montagna, O. Nicrosini, F. Piccinini
Program title: WWGENPV 2.0
Catalogue identifier: ADBU_v2_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 99(1997)355
Programming language: Fortran.
Computer: DEC ALPHA 3000.
Operating system: VMS, UNIX.
RAM: 450K words
Word size: 32
Keywords: Particle physics, Elementary, E+e- collisions, Lep, W-mass measurement, Radiative corrections, Corrections qed, Corrections qcd, Minimal standard model, Four-fermion final States, Electron structure Functions, Monte carlo integration, Event simulation, Hadronisation.
Classification: 11.2.

Subprograms used:
Cat Id Title Reference
ACTU_v1_0 PYTHIA 5.7 AND JETSET 7.4 CPC 82(1994)74
ACPR_v1_0 RANLUX CPC 79(1994)111

Nature of problem:
The precise measurement of the W-boson mass MW constitutes a primary task of the forthcoming experiments at the high energy electron-positron collider LEP2 (2MW <= sqrt(s) <= 210 GeV). A meaningful comparison between theory and experiment requires an accurate description of the fully exclusive processes e+e- -> 4f, including the main effects of radiative corrections, with the final goal of providing predictions for the distributions measured by the experiments.

Solution method:
Same as in the original program, as far as weighted event integration and unweighted event generation are concerned. Adaptive Monte Carlo integration for high numerical precision purposes is added. Optional hadronic interface in the generation branch is supplied.

Reasons for new version:
The most promising methods for measuring the W-boson mass at LEP2 are the so called "threshold" and "direct reconstruction" methods [5]. For the first one, a precise evaluation of the threshold cross section is required. For the second one, a precise description of the invariant- mass shape of the hadronic system in semileptonic decays is mandatory. In order to meet these requirements, the previous version of the program has been improved by extending the class of the tree-level EW diagrams taken into account, by including pT/pL effects both in initial- and final-state QED radiation, by supplying an hadronic interface in the generation branch.

Restrictions:
While the semileptonic decay channels are complete at the level of the Born approximation EW diagrams (CC11/CC20 diagrams), neutral current back-grounds are neglected in the fully hadronic and leptonic decay channels. QED radiation is treated at the leading logarithmic level. Due to the absence of a complete O(alpha)/O(alphas) diagrammatic calculation, the most relevant EW and QCD corrections are effectively incorporated according to the recipe given in [6]. No anomalous coupling effects are at present taken into account.

Unusual features:
Subroutines from the library of mathematical subprograms NAGLIB [3] for the numerical integrations are used in the program, when the adaptive integration branch is selected.

Running time:
As adaptive integrator, the code provides cross section and energy and invariant-mass losses with a relative accuracy of about 1 per cent in 8 min on HP 9000/735. As integrator of weighted events, the code produces about 10**5 events/min on the same system. The generation of a sample of 10**3 hadronised unweighted events requires about 8 min on the same system.

References:
[1] CERN Program Library, CN Division, CERN, Geneva.
[2] NAG Fortran Library Manual Mark 16 (Numerical Algorithms Group, Oxford, 1991).
[3] T. Sjostrand, Comp. Phys. Commun. 82 (1994) 74; Lund University Report LU TP 95-20 (1995).
[4] F. James, Comp. Phys. Commun. 79 (1994) 111.
[5] Physics at LEP2, CERN Report 96-01, Theoretical Physics and Particle Physics Experiments Divisions, G. Altarelli, T. Sjostrand and F. Zwirner, eds., Vols. 1 and 2, Geneva, 19 February 1996.
[6] W. Beenakker, F. Berends et al., "WW cross-sections and distributions", in
[5] , Vol. 1, pag. 79.