pythia8.C

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/// \file
/// \ingroup tutorial_pythia
/// pythia8 basic example
///
/// to run, do:
///
/// ~~~{.cpp}
///  root > .x pythia8.C
/// ~~~
///
/// Note that before executing this script, for some Pythia8 builds:
///
///  - the env variable PYTHIA8 must point to the pythia8100 (or newer) directory
///  - the env variable PYTHIA8DATA must be defined and it must point to $PYTHIA8/xmldoc
///
/// \macro_code
///
/// \author Andreas Morsch
 
#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)
{
// Load libraries
   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();
 
#if PYTHIA_VERSION_INTEGER == 8235
   // Pythia 8.235 is known to cause crashes:
   printf("ABORTING PYTHIA8 TUTORIAL!\n");
   printf("The version of Pythia you use is known to case crashes due to memory errors.\n");
   printf("They have been reported to the authors; the Pythia versions 8.1... are known to work.\n");
   return;
#endif
 
// Configure
   pythia8->ReadString("HardQCD:all = on");
   pythia8->ReadString("Random:setSeed = on");
   // use a reproducible seed: always the same results for the tutorial.
   pythia8->ReadString("Random:seed = 42");
 
 
// 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();
         Float_t charge = TDatabasePDG::Instance()->GetParticle(pdg)->Charge();
         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}");
 }