main35
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// main35.cc is a part of the PYTHIA event generator.
// Copyright (C) 2019 Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
// Please respect the MCnet Guidelines, see GUIDELINES for details.
// Author: Philip Ilten.
// Keywords: onia; helaconia;
// An example where the quarkonia hard process (p p -> J/psi g) is
// automatically produced externally with HelacOnia, read in, and the
// remainder of the event is then produced by Pythia (MPI, showers,
// and hadronization). A comparison is made between events produced
// with Pythia at LO and HelacOnia at LO.
// For this example to run, HelacOnia must be installed and the
// command "exe" (set by default as "ho_cluster") must be available
// via the command line. Note that this example has only been tested
// with HelacOnia version 2.2.4; due to rapid HelacOnia development,
// this example may not work with other versions. For more details on
// the LHAHelacOnia class see the comments of
// Pythia8Plugins/LHAHelacOnia.h.
#include "Pythia8/Pythia.h"
#include "Pythia8Plugins/LHAHelaconia.h"
using namespace Pythia8;
//==========================================================================
// A simple method to run Pythia, analyze the events, and fill a histogram.
void run(Pythia* pythia, Hist& hist, int nEvent) {
pythia->readString("Random:setSeed = on");
pythia->readString("Random:seed = 1");
pythia->init();
for (int iEvent = 0; iEvent < nEvent; ++iEvent) {
if (!pythia->next()) continue;
for (int i = 0; i < pythia->event.size(); ++i) {
if (pythia->event[i].id() != 443) continue;
hist.fill(pythia->event[pythia->event[i].iBotCopyId()].pT());
break;
}
}
pythia->stat();
}
//==========================================================================
int main() {
// The name of the HelacOnia executable.
// You must prepend this string with the path to the executable
// on your local installation, or otherwise make it available.
string exe("ho_cluster");
// Create the histograms.
Hist pyPtPsi("Pythia dN/dpT J/psi", 100, 0., 20.);
Hist hoPtPsi("HelacOnia dN/dpT J/psi", 100, 0., 20.);
// Produce leading-order events with Pythia.
Pythia* pythia = new Pythia();
pythia->readString("Beams:eCM = 13000.");
pythia->readString("Charmonium:gg2ccbar(3S1)[3S1(1)]g = on,off");
pythia->readString("PhaseSpace:pTHatMin = 2");
run(pythia, pyPtPsi, 1000);
delete pythia;
// Produce leading-order events with HelacOnia.
pythia = new Pythia();
LHAupHelaconia helaconia(pythia, "helaconiarun", exe);
helaconia.readString("generate g g > cc~(3S11) g");
helaconia.readString("set energy_beam1 = 6500");
helaconia.readString("set energy_beam2 = 6500");
helaconia.readString("set minptconia = 2");
pythia->setLHAupPtr(&helaconia);
run(pythia, hoPtPsi, 1000);
delete pythia;
// Print the histograms.
cout << pyPtPsi;
cout << hoPtPsi;
return 0;
}