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Manuscript Title: Monte Carlo simulation of two-photon processes. II. Complete lowest order calculations for four-lepton production processes in electron- positron collisions.
Authors: F.A. Berends, P.H. Daverveldt, R. Kleiss
Program title: DIAG36
Catalogue identifier: AAFH_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 40(1986)285
Programming language: Fortran.
Computer: AMDAHL V7B.
Word size: 32
Keywords: Elementary, Particle physics, Two-photon process, Four-lepton production, Process, Monte carlo simulation, Event generator, E+e- collisions, Event simulation, Electron, Positron, Lepton, Quark.
Classification: 11.2.

Nature of problem:
Four-lepton processes such as e+e- -> e+e+e-e-, e+e- -> e+e-mu+mu-, e+e- -> mu+mu+mu-mu-, e+e- -> mu+mu-tau+tau- are described by a (sub) set of 36 Feynman diagrams. In the e+e- -> e+e+e-e- case all these graphs contribute and give rise to 657 different peaks of the differential cross section in a seven dimensional phase-space. The MC program presented here can produce unweighted events for these processes, while all masses and peaks are properly taken into account. Moreover, it can also be used for the simulation of e+e- -> e+e-q q- and e+e- -> mu+mu-q q-.

Solution method:
The 36 diagrams are divided into four groups. For each group we design a separate generator in which all the phase-space variables have been chosen such that the peaking structure is well described. The interference between the groups is taken care of by the assignment of a weight to the events. Each event is first obtained according to one out of four approximate distributions by the corresponding generator. We account for the approximations used by imposing a weight on the events. Upon the application of a rejection algorithm we are left with unweighted events.

Restrictions:
This program has especially been designed for the no-tagging case. Moreover, when we simulate e+e- -> e+e+e-e- we assume that the cuts are applied to all final state particles. Other cuts can only be dealt with after the event generation by setting the weights equal to zero of those events that do not satisfy these cuts.

Running time:
500 events/CPU minute.