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Manuscript Title: The Monte Carlo program KoralW version 1.51 and the concurrent Monte Carlo KoralW&YFSWW3 with all background graphs and first-order corrections to W-pair production.
Authors: S. Jadach, W. Placzek, M. Skrzypek, B.F.L. Ward, Z. Was
Program title: KoralW, version 1.51
Catalogue identifier: ADCT_v3_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 140(2001)475
Programming language: Fortran.
Computer: PC Pentium III, 800 MHz.
Operating system: UNIX, Linux version 6.x and 7.x.
RAM: 25M words
Keywords: Radiative corrections, Initial-state radiation (ISR), O(alpha) electroweak (EW) corrections, Leading-logarithmic (LL) approximation, Heavy boson W, Four-fermion processes, Monte Carlo (MC) simulation/generation, Quantum electrodynamics (QED), Quantum chromodynamics (QCD), Yennie-Frautschi-Suura (YFS) exponentiation, Standard Model (SM), LEP2, Next-generation, Linear colliders (LC), Elementary particle physics, Event simulation.
Classification: 11.2.

Nature of problem:
The precise study of W-pair production and decay at LEP2 requires both non-double-resonant and O(alpha) corrections. So far each of these corrections is available as a separate Monte Carlo program and there is no Monte Carlo that could simulate in a complete way both effects at the same time. Such a MC event generator would be of importance, for example, for apparatus simulations or Monte Carlo based fits. The previous version of KoralW [1] included all non-double-resonant corrections to all double-resonant four-fermion processes in e+e- annihilation. The present version 1.51. allows, for the first time ever, the inclusion on an event-per-event basis of the respective O(alpha) corrections generated at the same time by the independently running Monte Carlo program YFSWW3 [2], as well as a reweighting of any earlier generated events with modified parameter sets.

Solution method:
The Monte Carlo method used to simulate the all four-fermion final-state processes in e+e- collisions in the presence of multiphoton initial-state radiation has not changed since version 1.42 [1]. Adding the O(alpha) corrections generated by YFSWW3 is done at the level of the UNIX/Linux operating system with the help of the FIFO mechanism ("named pipes").

For KoralW as in version 1.42 [1] (ADCT_v2_0); for KoralW&YFSWW3 as in [1,2] (ADCT_v1_0 & ADOU_v1_0).

Running time:
Approximate times on a PC Pentium III @ 800 MHz for cuts as described in this article: 5 minutes per 1000 constant-weight CCall events (KoralW stand-alone); 50 minutes per 1000 constant-weight CCall events with the O(alpha) correction (the CMC KoralW&YFSWW3, max. weight for rejection increased by a factor 2).

[1] S. Jadach et al., Comput. Phys. Commun. 119 (1999) 272.
[2] S. Jadach et al., The Monte Carlo event generator YFSWW3 version 1.16 for W-pair production and decay at LEP2/LC energies, Preprint CERN-TH/2001-017, UTHEP-01-0101, January 2001, hep-ph/0103163; Comput. Phys. Commun. 140 (2001) 432.