Programs in Physics & Physical Chemistry
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|Manuscript Title: BBBREM, Monte Carlo simulation of radiative Bhabha scattering in the very forward direction.|
|Authors: R. Kleiss, H. Burkhardt|
|Program title: BBBREM|
|Catalogue identifier: ACTW_v1_0|
Distribution format: gz
|Journal reference: Comput. Phys. Commun. 81(1994)372|
|Programming language: Fortran.|
|RAM: 200K words|
|Word size: 32|
|Keywords: Particle physics, Elementary, Qed, Bhabha scattering, Bremsstrahlung, Radiative processes, Forward scattering, Collinear singularities, Monte carlo simulation, Experimental cuts, Beam lifetimes, Luminosity monitoring.|
Nature of problem:
Radiative Bhabha scattering, e+e- -> e+e-gamma, has a very large cross section at small scattering angles, and plays various roles in existing and future e+e- colliders. It can be an important background to several two-photon scattering processes; it forms the major ingredient in the finite lifetime of colliding beams; and it is a possible process by which the luminosity can be measured, by observing electrons or photons emerging at zero scattering angle. Accurate knowledge of its cross section is therefore important.
Due to the extremely singular structure of the matrix elements, and the possibility of complicated or unusual experimental cuts, a straight- forward integration of the cross section over the allowed phase space is impractical. We therefore construct a Monte Carlo algorithm that generates (random) events in phase space, with a distribution that matches the actual cross section as closely as possible. These events are assigned a weight which corrects for discrepancies between the actual and the approximate matrix elements: the average value of the weight in a sample of generated events is the Monte Carlo estimate of the cross section. Since each generated event is a complete description of the momenta of the produced particles, any conceivable experimental cut can be implemented, in addition to the single a-priori constraint, namely, a minimum value for the energy of the Bremsstrahlung photon. This value can be set (to essentially arbitrarily small values) by the user. By setting the weight of events that fail a particular set of cuts to zero, one obtains the cross section under those cuts.
about 185 musec per generated event on SUN SPACR 10; about 40 musec per generated event on IBM 9000.
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