next up previous
Next: Introduction

CERN-TH/96-158
UTHEP-96-0601

Upgrade of the Monte Carlo program BHLUMI
for Bhabha scattering at low angles to version 4.04

S. Jadach
Institute of Nuclear Physics, ul. Kawiory 26a, Kraków, Poland
CERN, Theory Division, CH-1211 Geneva 23, Switzerland
W. Paczek
Department of Physics and Astronomy,
The University of Tennessee, Knoxville, TN 37996-1200,
E. Richter-Was
Institute of Computer Science, Jagellonian University,
Kraków, ul. Reymonta 4, Poland,
CERN, Theory Division, CH-1211 Geneva 23, Switzerland
B.F.L. Ward
Department of Physics and Astronomy,
The University of Tennessee, Knoxville, TN 37996-1200,
SLAC, Stanford University, Stanford, CA 94309
Z. Was
Institute of Nuclear Physics, Kraków, ul. Kawiory 26a, Poland,
CERN, Theory Division, CH-1211 Geneva 23, Switzerland

Abstract:

The new version of the Monte Carlo program for small-angle Bhabha scattering BHLUMI with an overall precision of 0.11% is presented. The main improvements are in the matrix element of the main multi-photon sub-generator based on the Yennie-Frautschi-Suura exponentiation, where the missing second-order terms in the leading-logarithmic (LL) approximation are supplemented and the contribution from the Z resonance is improved. In the LUMLOG sub-generator based on the LL approximation, we implement collinear photon emission in the final state and we also add a down-graded third-order LL matrix element, which has exactly the same incomplete third-order LL contribution as the multi-photon BHLUMI. The new LUMLOG is therefore capable of calculating the missing third-order LL part in the cross sections obtained from the main multi-photon event generator, for arbitrary event selection. The first-order event generator OLDBIS remains unchanged.

Submitted to Computer Physics Communications

Work supported in part by the US DoE contract DE-FG05-91ER40627, Polish Government grants KBN 2P30225206, 2P03B17210, the European Union contract No. ERB-CIPD-CT94-0016 and Polish-French Collaboration within IN2P3.
On leave of absence from Institute of Computer Science, Jagellonian University, Kraków, Poland.

CERN-TH/96-158
UTHEP-96-0601
June 1996

NEW VERSION SUMMARY

Title of the program: BHLUMI version 4.04
Reference to original program: Comput. Phys. Commun. 70 (1992) 305
Computer: IBM rs6000, HP9000 and other UNIX workstations
Operating system: UNIX
Programming language used: FORTRAN 77
High speed storage required: < 5 MB
No. of bits in a word: 32
Peripherals used: Line printer
No. of cards in combined program and test deck: about 12000
Keywords: Radiative corrections, Monte Carlo simulation, Bhabha scattering, bremsstrahlung, Quantum Electrodynamics (QED), electroweak theory, structure functions.
Nature of physical 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 multiple emission of the bremsstrahlung photons.
Method of solution: 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 on the complexity of the problem: The overall precision of the QED calculation is restricted to 0.11%, for a typical LEP/SLC luminometer angular range of , where is the scattering angle.
Typical 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.

LONG WRITE--UP


next up previous
Next: Introduction


Stanislaw Jadach
Wed Sep 25 11:12:40 METDST 1996