GR@PPA 2.8: Initial-state jet matching for weak-boson production processes at hadron collisions

Abstract

The initial-state jet matching method introduced in our previous studies has been applied to the event generation of single W and Z production processes and diboson (W+W−, WZ and ZZ) production processes at hadron collisions in the framework of the GR@PPA event generator. The generated events reproduce the transverse momentum spectra of weak bosons continuously in the entire kinematical region. The matrix elements (ME) for hard interactions are still at the tree level. As in previous versions, the decays of weak bosons are included in the matrix elements. Therefore, spin correlations and phase-space effects in the decay of weak bosons are exact at the tree level. The program package includes custom-made parton shower programs as well as ME-based hard interaction generators in order to achieve self-consistent jet matching. The generated events can be passed to general-purpose event generators to make the simulation proceed down to the hadron level. Program summaryProgram title: GR@PPA 2.8Catalogue identifier: ADRH_v3_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADRH_v3_0.htmlProgram obtainable from: CPC Program Library, Queenʼs University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 112 146No. of bytes in distributed program, including test data, etc.: 596 667Distribution format: tar.gzProgramming language: Fortran; with some included libraries coded in C and C++Computer: AllOperating system: Any UNIX-like systemRAM: 1.6 Mega bytes at minimumClassification: 11.2Catalogue identifier of previous version: ADRH_v2_0Journal reference of previous version: Comput. Phys. Comm. 175 (2006) 665External routines: Bash and Perl for the setup, and CERNLIB, ROOT, LHAPDF, PYTHIA according to the userʼs choice.Does the new version supersede the previous version?: No, this version supports only a part of the processes included in the previous versions.Nature of problem: We need to combine those processes including 0 jet and 1 jet in the matrix elements using an appropriate matching method, in order to simulate weak-boson production processes in the entire kinematical region.Solution method: The leading logarithmic components to be included in parton distribution functions and parton showers are subtracted from 1-jet matrix elements. Custom-made parton shower programs are provided to ensure satisfactory performance of the matching method.Reasons for new version: An initial-state jet matching method has been implemented.Summary of revisions: Weak-boson production processes associated with 0 jet and 1 jet can be consistently merged using the matching method.Restrictions: The built-in parton showers are not compatible with the PYTHIA new PS and the HERWIG PS.Unusual features: A large number of particles may be produced by the parton showers and passed to general-purpose event generators.Running time: About 10 min for initialization plus 25 s for every 1k-event generation for W production in the LHC condition, on a 3.0-GHz Intel Xeon processor with the default setting.