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Manuscript Title: The Lund Monte Carlo for jet fragmentation and e+e- physics: JETSET version 6.3 - an update.
Authors: T. Sjostrand, M. Bengtsson
Program title: JETSET 6.3
Catalogue identifier: AAFP_v2_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 43(1987)367
Programming language: Fortran.
Computer: ND-570.
Operating system: SINTRAN III - VSX/500.
RAM: 50K words
Word size: 32
Keywords: Elementary, Particle physics, Jet fragmentation, Hadronization, Multiparticle production, Quark jet, Gluon jet, E+e- annihilation, Parton showers, Leading log evolution, Onium decays, Event analysis, Cluster algorithm, Monte carlo Event simulation.
Classification: 11.2.

Nature of problem:
The theory of strong interactions, QCD, cannot be solved to describe the process of hadronization, i.e. how the primary partons are transformed into the observable hadrons in high energy interactions. The probability for a given parton configuration is often known (approximately) from perturbative QCD, however.

Solution method:
A phenomenological model, the Lund string model, is introduced to describe the hadronization of an initial parton configuration. Different independent fragmentation schemes are available as alternatives. Subsequent particle decays are also considered. For e+e- annhiliation, matrix elements and parton showers are combined to give primary parton configurations. A number of general utility routines are also included. The program presented here is largely compatible with the previous version, JETSET 6.2. (Comp. Phys. Commun. 39(1986)347).

Restrictions:
At very high energies, the program may break down for one of two reasons, either the number of particles may exceed the memory space available, or the (mainly) single-precision kinematics may give unacceptable roundoff errors.

Unusual features:
A random number generator is required.

Running time:
Depends very much on the energy and nature of the system, but is roughly proportional to the number of particles produced. A 40 GeV e+e- annihilation event, with an average of 32 particles (of which 15 are charged) takes approximately 0.15 s with parton showers and 0.05 s with matrix elements.