GR@PPA 2.9: Radiation matching for simulating photon production processes in hadron collisions

Abstract

We release an event generator package GR@PPA 2.9, for simulating the direct (single) photon and diphoton (double photon) production in hadron collisions. The included programs were used in our previous studies, in which we have explicitly shown large contributions from parton-associated processes. The programs consistently combine simulations based on matrix elements with parton-shower simulations that reproduce the multiple parton radiation and quark fragmentation to photons. The matrix elements include associated parton production processes up to two partons. We provide instructions for the installation and execution of the programs in this article. The practical performance is also presented. Program summaryProgram Title: GR@PPA 2.9Program Files doi:http://dx.doi.org/10.17632/7838c8djsr.1Licensing provisions: GPLv3Programming language: Fortran; with some included libraries coded in C and C++External routines/libraries: bash and Perl for the setup, and CERNLIB, ROOT, LHAPDF 5, PYTHIA 6.4 according to the choice of usersJournal reference of previous version: Comput. Phys. Comm. 183 (2012) 1014–1028Does the new version supersede the previous version?: No, this version supports processes not included in previous versions.Nature of problem: It is necessary to include jet-associated processes up to two jets for realistic simulations of photon production processes in high-energy hadron collisions. Photons also need to be considered as radiation. An appropriate matching method has to be introduced for combining those processes having different jet and photon multiplicities and parton shower simulations.Solution method: The limited leading-log (LLL) subtraction method has been extended to multi-jet processes and those including photon radiation. The final-state parton shower simulation has been improved to support QED photon radiation.Reasons for the new version: New processes have been supported.Summary of revisions: This program package provides event generators for realistic simulations of single and double photon production processes in high-energy hadron collisions. Users can consistently combine different jet- and photon-multiplicity processes up to two jets and two photons.