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Manuscript Title: NEXTCALIBUR - a four-fermion generator for electron-positron collisions.
Authors: F.A. Berends, C.G. Papadopoulos, R. Pittau
Program title: NEXTCALIBUR
Catalogue identifier: ADNS_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 136(2001)148
Programming language: Fortran.
Computer: DIGITAL-ALPHA, HP.
Operating system: UNIX.
RAM: 500K words
Word size: 32
Keywords: Elementary particle physics, QCD, Decaying vector-boson production, All massive four- fermion processes, Electroweak background, Initial state pt dependent QED radiation, Recursive Dyson- Schwinger equations, Multi-channel Monte Carlo approach.
Classification: 11.5.

Nature of problem:
Four-fermion production is and will be investigated at e+e- colliders in a wide range of energies. Fermion masses have to be included when studying Higgs boson production and processes with forward scattered electrons. A Monte Carlo program being able to take into account both signal and background electroweak diagrams for four-fermion processes, without neglecting fermion masses, is therefore required. Higher order effects, such as the QED radiation evaluated at the proper scale, have also to be included, together with the possibility of generating photons with a non vanishng pt spectrum. For t-channel dominated processes, the correct running of alphaEM must be implemented.

Solution method:
An event generator is the most suitable choice for a program to be able to deal with the above physical problems. For the matrix element evaluation, recursive Dyson-Schwinger equations that express the n-point Green's functions in terms of the 1-, 2-, ..., (n-1)-point functions are used. The Monte Carlo integration is performed by using an efficient self-optimizing multi-channel approach.

Unusual features:
By changing compilation procedure, the program can run both in double and quadruple precision.

Running time:
About 250 weighted events per second, in double precision on DIGITAL- ALPHA/21164 DS20 (500MHz), depending on the chosen physical process.