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Manuscript Title: The Monte Carlo event generator YFSWW3 version 1.16 for W-pair production and decay at LEP2/LC energies.
Authors: S. Jadach, W. Placzek, M. Skrzypek, B.F.L. Ward, Z. Was
Program title: YFSWW3, version 1.16
Catalogue identifier: ADOU_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 140(2001)432
Programming language: Fortran.
Computer: PC Intel Pentium III.
Operating system: UNIX/Linux.
RAM: 10M words
Keywords: Standard Model (SM), LEP2, Linear colliders (LC), Quantum electrodynamics (QED), Quantum chromodynamics (QCD), Boson W, W-pair production, W decay, W branching ratio (BR), Triple guage boson couplings (TGC), Quartic guage boson couplings (QGC), Four-fermion (4f) background, Radiative corrections, Yennie-Frautschi-Suura (YFS) exponentiation, Initial-state radiation (ISR), Leading-log (LL) approximation, Coulomb effect, Final-state radiation (FSR), Electroweak (EW) corrections, Leading-pole approximation (LPA), Monte Carlo (MC) simulation/generation, Elementary particle physics, Event simulation.
Classification: 11.2.

Nature of problem:
The process of the W-pair production is important for precise tests of the Standard Model as well as searches for "new physics" at LEP2 and future linear colliders. In order to match the experimental precision necessary for a successful physics programme, quantum effects (the so-called radiative corrections) have to be included into a theoretical description of this process. It turns out that not only the so-called universal corrections (initial-state radiation, the Coulomb effect, "naive" QCD corrections, etc.) are necessary, but also the O(alpha) electroweak corrections in the WW production are needed to reach the desired theoretical accuracy. All these effects should, preferably, be included in a Monte Carlo event generator in order to account for realistic experimental set-ups.

Solution method:
The Monte Carlo event generator for the combined W-pair production and decay process including O(alpha**3) LL ISR effects, the Coulomb correction (usual or screened), the "naive" QCD effect, the O(alpha) EW corrections in the WW production stage, implemented within the YFS exclusive exponentiation framework is provided. Multiphoton radiation in the WW production is generated according to the YFS MC method. The photon radiation in the W decays, normalized to the W BRs, is generated by the LL-type MC program PHOTOS (up to two photons). The decays of tau's including radiative corrections are simulated by the dedicated package TAUOLA. The quark fragmentation/hadronization is performed with the help of the Lund program JETSET. The program can provide both weighted and unweighted (weight = 1) events. Any experimental cut and apparatus efficiency may be introduced easily by rejecting some of the generated events.

The LPA is used (in two versions) to describe the signal WW production process. Multiphoton radiation according to the YFS exponentiation scheme is generated only for the WW production stage. O(alpha) EW corrections (in LPA) are included only in the WW production stage. The ISR effects beyond O(alpha) are included in the LL approximation. Non-factorizable corrections (interferences between the production and decay stages) are approximated by the so-called screened Coulomb ansatz. Spin correlations between the WW production and decays are fully included only at the Born and the ISR levels. Radiative corrections in the W decays are included into an overall normalization through the W BRs, and the real photon radiation is generated in the LL approximation (up to two photons) by the program PHOTOS. Anomalous triple gauge boson couplings are included in the Born-like matrix element, i.e. with the universal SM corrections only. Quartic gauge boson couplings are implemented according to the Standard Model only (no anomalous couplings). The tau decays and quark hadronization are performed, respectively, with the help of the dedicated packages TAUOLA and JETSET. No 4f background processes are included.

Running time:
200 CPU seconds of a PC Intel Pentium III @ 550 MHz per 1000 unweighted events, for the parameter settings as they are given in the demonstration program.