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main53.cc
1 // main53.cc is a part of the PYTHIA event generator.
2 // Copyright (C) 2014 Peter Skands, Torbjorn Sjostrand.
3 // PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
4 // Please respect the MCnet Guidelines, see GUIDELINES for details.
5 
6 // This is a simple test program.
7 // It illustrates how to interface an external process with an incoming photon
8 // in a hadron beam, using the MRST2004QED PDF set.
9 // All input apart from the name of the external LHEF file is specified in the
10 // main53.cmnd file.
11 
12 #include "Pythia8/Pythia.h"
13 
14 using namespace Pythia8;
15 
16 int main() {
17 
18  // Generator. Shorthand for the event.
19  Pythia pythia;
20  Event& event = pythia.event;
21 
22  // Read in commands from external file.
23  pythia.readFile("main53.cmnd");
24 
25  // Extract settings to be used in the main program.
26  int nEvent = pythia.mode("Main:numberOfEvents");
27 
28  // Initialize. Either of two opions, to be picked in main53.cmnd.
29  // 1) Read in external event with incoming photon in the ME,
30  // from pre-generated .lhe file (thanks to SANC and R. Sadykov).
31  // 2) Use internal fermion gamma -> W+- fermion' process.
32  pythia.init();
33 
34  // Histograms for pT distribution in gluon production vertex.
35  Hist pTprim( "pT of photon production, no ISR", 100, 0., 100.);
36  Hist pTwith( "pT of photon production, with ISR", 100, 0., 100.);
37 
38  // Begin event loop.
39  for (int iEvent = 0; iEvent < nEvent; ++iEvent) {
40 
41  // Generate events. Quit if failure.
42  if (!pythia.next()) {
43  break;
44  }
45 
46  // Analyze event to find branching where photon is produced.
47  int iGam = (event[3].id() == 22) ? 3 : 4;
48  int iGamMother = iGam;
49  for ( ; ; ) {
50  iGamMother = event[iGam].mother1();
51  if (iGamMother < iGam || event[iGamMother].id() != 22) break;
52  iGam = iGamMother;
53  }
54 
55  // Find and histogram pT in this branching.
56  if (iGamMother < iGam) pTprim.fill( event[iGam].pT() );
57  else {
58  int iQ = iGamMother;
59  int size = event.size();
60  do ++iQ;
61  while (event[iQ].status() != -43 && iQ < size - 1);
62  if (event[iQ].status() == -43) pTwith.fill( event[iQ].pT() );
63  }
64 
65  // End of event loop.
66  }
67 
68  // Final statistics and histogram output.
69  pythia.stat();
70  cout << pTprim << pTwith;
71 
72  return 0;
73 }
74