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Manuscript Title: GR@PPA 2.7 event generator for pp/ppbar collisions
Authors: S. Tsuno, T. Kaneko, Y. Kurihara, S. Odaka, K. Kato
Program title: GR@PPA (v2.7)
Catalogue identifier: ADRH_v2_0
Journal reference: Comput. Phys. Commun. 175(2006)665
Programming language: Fortran77.
Computer: Unix systems with a Fortran compiler.
Operating system: UNIX.
RAM: 56.5 kwords for an integration, 74.6 kwords for an event generation
Keywords: GR@PPA, GRACE, PYTHIA, HERWIG, pp/ppbar collisions.
PACS: 11.80.Cr, 12.38.Bx, 13.87.-a.
Classification: 11.2.

Does the new version supersede the previous version?: Yes. The new version includes all functions from the previous version plus newly developed functions.

Nature of problem:
The multi-legs interaction processes have become more important with increasing the colliding energy available at the high energy collider experiments. At hadron-collider experiments, since thousands of Feynman diagrams contributes in the single ineraction process, the faster and more stable calculation to obtain the results is desirable.

Solution method:
GR@PPA is an event generator for V (W or Z) + jets (≤ 4 jets), VV + jets (≤ 2 jets) and QCD multi-jet (≤ 4 jets) production processes at pp and ppbar collisions, in addition to the four bottom quark productions implemented in our previous work (GR@PPA_4b). Also included are the top-pair and top-pair + jet production processes. In this version, the GR@PPA framework and the process dependent matrix-element routines are separately provided. This makes it easier to add further new processes, and allows users to make a choice of processes to implement. This version also has several new features to handle complicated multi-body production processes. A systematic way to combine many subprocesses to a single base-subprocess has been introduced, and a new method has been adopted to calculate the color factors of complicated QCD processes. They speed up the calculation significantly.

Reasons for new version:
see Nature of Problem above.

Summary of revisions:
see Solution method above.

Restrictions:
The interference between decay fermions from the boson and those from other sources is ignored in the diagram calculation.

Additional comments:
GR@PPA accesses CPC sub-programs PYTHIA, HERWIG, BASES, SPRING. The BASES/SPRING package is included in the GR@PPA(v2.7) distribution, but the PYTHIA (ACTU_v1_0) and HERWIG (ACBY_v1_0) programs are not. It is, however, possible to run the program as a standalone without using these libraries.

Running time:
2 hours for a cross-section integration and 200 msec per 1 event for an event generation.