Elsevier Science Home
Computer Physics Communications Program Library
Full text online from Science Direct
Programs in Physics & Physical Chemistry
CPC Home

[Licence| Download | New Version Template] aafj_v1_0.gz(40 Kbytes)
Manuscript Title: Monte Carlo simulation of two-photon processes. III. Complete lowest order calculations for e+e- -> e+e-mu+mu- with large angle tagging conditions.
Authors: F.A. Berends, P.H. Daverveldt, R. Kleiss
Program title: DIAG12NST
Catalogue identifier: AAFJ_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 40(1986)309
Programming language: Fortran.
Computer: AMDAHL V7B.
Word size: 32
Keywords: Elementary, Particle physics, Event simulation, Two-photon process, Monte carlo simulation, Event generator, E+e- collision, Large angle tagging, Electron, Positron, Muon.
Classification: 11.2.

Nature of problem:
Single tagging conditions have to be applied to two-photon processes when one wants to measure the four-momentum of one of the virtual photons in the 'multiperipheral' Feynman diagrams in order to obtain information on e.g. the Q**2 dependence of the photon structure function. The program, presented here, generates unweighted events for the process e+e- -> e+e-mu+mu- and calculates exact total and differential cross sections on the basis of all twelve Feynman diagrams contributing in lowest order (alpha**4). Moreover, it allows the user to specify beforehand the minimum and maximum scattering angle of one of the beam particles. Consequently the efficiency of the program is approximately equal to that of the no-tagging Monte Carlo program.

Solution method:
The method applied resembles closely the one described in Comp. Phys. Commun. 40(1986)285. Again the events are generated by the use of four subgenerators. The subgenerators for the multiperipheral and bremsstrahlung Feynman diagrams are now changed in such a way that the produced events directly fulfil a cut on the scattering angle of the positron beam. The subgenerators for the conversion and annihilation group have not been changed because the dominant part of the cross section corresponds to events which lie completely in the central detector, so that only little efficiency will be lost by throwing away those events where the scattered positron angle does not satisfy the cut.

In the program the positron beam is chosen to be scattered over a large angle. The scattering angle of the electron beam can only be restricted by an upper bound. The program runs most efficiently with an anti-tag cut on the electron: i.e. the maximum scattering angle of the electron is smaller than the minimum scattering angle of the positron beam. Consequently the program is not well suited to simulate double-tagging experiments.

Running time:
500 events/ CPU minute.