Logo ROOT   6.10/09
Reference Guide
pythia8.C File Reference

Detailed Description

pythia8 basic example

to run, do:

root > .x pythia8.C

Note that before executing this script,

#include "TSystem.h"
#include "TH1F.h"
#include "TClonesArray.h"
#include "TPythia8.h"
#include "TParticle.h"
#include "TDatabasePDG.h"
#include "TCanvas.h"
void pythia8(Int_t nev = 100, Int_t ndeb = 1)
{
const char *p8dataenv = gSystem->Getenv("PYTHIA8DATA");
if (!p8dataenv) {
const char *p8env = gSystem->Getenv("PYTHIA8");
if (!p8env) {
Error("pythia8.C",
"Environment variable PYTHIA8 must contain path to pythia directory!");
return;
}
TString p8d = p8env;
p8d += "/xmldoc";
gSystem->Setenv("PYTHIA8DATA", p8d);
}
const char* path = gSystem->ExpandPathName("$PYTHIA8DATA");
if (gSystem->AccessPathName(path)) {
Error("pythia8.C",
"Environment variable PYTHIA8DATA must contain path to $PYTHIA8/xmldoc directory !");
return;
}
// Load libraries
#ifndef G__WIN32 // Pythia8 is a static library on Windows
if (gSystem->Getenv("PYTHIA8")) {
gSystem->Load("$PYTHIA8/lib/libpythia8");
} else {
gSystem->Load("libpythia8");
}
#endif
gSystem->Load("libEG");
gSystem->Load("libEGPythia8");
// Histograms
TH1F* etaH = new TH1F("etaH", "Pseudorapidity", 120, -12., 12.);
TH1F* ptH = new TH1F("ptH", "pt", 50, 0., 10.);
// Array of particles
TClonesArray* particles = new TClonesArray("TParticle", 1000);
// Create pythia8 object
TPythia8* pythia8 = new TPythia8();
// Configure
pythia8->ReadString("HardQCD:all = on");
// Initialize
pythia8->Initialize(2212 /* p */, 2212 /* p */, 14000. /* TeV */);
// Event loop
for (Int_t iev = 0; iev < nev; iev++) {
pythia8->GenerateEvent();
if (iev < ndeb) pythia8->EventListing();
pythia8->ImportParticles(particles,"All");
Int_t np = particles->GetEntriesFast();
// Particle loop
for (Int_t ip = 0; ip < np; ip++) {
TParticle* part = (TParticle*) particles->At(ip);
Int_t ist = part->GetStatusCode();
// Positive codes are final particles.
if (ist <= 0) continue;
Int_t pdg = part->GetPdgCode();
if (charge == 0.) continue;
Float_t eta = part->Eta();
Float_t pt = part->Pt();
etaH->Fill(eta);
if (pt > 0.) ptH->Fill(pt, 1./(2. * pt));
}
}
pythia8->PrintStatistics();
TCanvas* c1 = new TCanvas("c1","Pythia8 test example",800,800);
c1->Divide(1, 2);
c1->cd(1);
etaH->Scale(5./Float_t(nev));
etaH->Draw();
etaH->SetXTitle("#eta");
etaH->SetYTitle("dN/d#eta");
c1->cd(2);
gPad->SetLogy();
ptH->Scale(5./Float_t(nev));
ptH->Draw();
ptH->SetXTitle("p_{t} [GeV/c]");
ptH->SetYTitle("dN/dp_{t}^{2} [GeV/c]^{-2}");
}
Author
Andreas Morsch

Definition in file pythia8.C.