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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.

Restrictions:
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.