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Manuscript Title: Upgrade of the Monte Carlo program BHLUMI for Bhabha scattering at low angles to version 4.04.
Authors: S. Jadach, W. Placzek, E. Richter-Was, B.F.L. Ward, Z. Was
Program title: BHLUMI version 4.04
Catalogue identifier: ACHI_v2_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 102(1997)229
Programming language: Fortran.
Computer: IBM RS6000.
Operating system: UNIX.
RAM: 5M words
Word size: 32
Keywords: Particle physics, Elementary, Corrections radiative, Monte carlo simulation, Bhabha scattering, Bremsstrahlung, Quantum electrodynamics, Electroweak theory, Structure functions.
Classification: 11.4.

Nature of problem:
The small-angle Bhabha scattering process is used in all electron- positron colliders to calculate machine luminosity. This process is subject to QED radiative corrections, which have to be known for arbitrary cut-offs and/or acceptance with a precision at least a factor of 2 better than the pure experimental precision. This means that the level of 0.05% should be reached. A realistic simulation should include emission of the bremsstrahlung photons.

Solution method:
The Monte Carlo simulation of the small-angle process is an ideal solution. It provides the integrated cross-section for arbitrary cuts. Direct simulation of the final state electrons and photons is precisely what is needed for detector simulation purposes.

The overall precision of the QED calculation is restricted to 0.11%, for a typical LEP/SLC luminometer angular range of 1o < theta < 3o, where theta is the scattering angle.

Running time:
The efficiency for multi-photon sub-generator is typically 6 million variable-weight events and 4 million constant-weight events per hour for an HP9000-735/100 MHz machine.