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Manuscript Title: The precision Monte Carlo event generator KK for two-fermion final states in e+e- collisions.
Authors: S. Jadach, B.F.L. Ward, Z. Was
Program title: KK version 4.12
Catalogue identifier: ADMD_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 130(2000)260
Programming language: Fortran.
Computer: IBM PowerPC M43P240.
Operating system: UNIX, AIX 4.x, HP-UX 10.x, Linux.
RAM: 10M words
Keywords: Particle physics, Elementary, Quantum electrodynamics (QED), Standard model, Electroweak interactions, Heavy boson Z, Spin polarization, Spin correlations, Radiative corrections, Initial-state radiation (ISR), Final-state radiation (FSR), QED interference, Monte Carlo (MC) simulation and generation, Coherent exclusive exponentiation (CEEX), Yennie-Frautschi-Suura (YFS) exponentiation, LEP2, Linear collider, TESLA, Event simulation.
Classification: 11.2.

Nature of problem:
The fermion pair production is and will be used as an important data point for precise tests of the standard electroweak theory at LEP and future linear colliders at higher energies. QED corrections to fermion pair production (especially tau leptons) at c-quark and b-quark factories has to be known to second order, including spin polarization effects. The Standard Model predictions at the per mille precision level, taking into account multiple emission of photons for realistic experimental acceptance, can only be obtained using a Monte Carlo event generator.

Solution method:
The Monte Carlo methods are used to simulate most of the two-fermion final-state processes in e+e- collisions in the presence of multiphoton initial-state radiation. The latter is described in the framework of exclusive coherent exponentiation (CEEX) based on Yennie-Frautschi-Suura exclusive exponentiation (YFS/EEX). CEEX treats correctly to infinite order not only infrared cancellations but also QED interferences and narrow resonances. The matrix element according to standard YFS exponentiation is also provided for tests. For quarks and tau leptons, the appropriate simulation of hadronization or decay is included. Beam polarization and spin effects, both longitudinal and transverse, in tau decays are properly taken into account.

Restrictions:
In the present version, electron (Bhabha), neutrino and top quark final states are not included (they will be in a future version). Additional fermion pair production is not included. Third-order QED corrections in leading-logarithmic approximation are included only in the auxiliary YFS/EEX matrix element (which can be activated with the help of input parameters). Electroweak corrections should not be trusted above the t-quark threshold. The total cross section for light quarks for sqrt(s)<10 GeV requires an improvement using experimental data.

Running time:
On the IBM PowerPC M43P240 installation (266 MHz, 65 CERN units) 4 sec per constant-weight event are needed. This result is for a default/recommended setting of the input parameters, with all hadronization/decay libraries switched ON.