// main282.cc is a part of the PYTHIA event generator.
// Copyright (C) 2026 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.

// Keywords: pythia 6; process cross sections

// Comparison with some PYTHIA 6.413 cross sections process by process.
// Several processes have been left out to keep reasonable execution time.
// Some processes are not handled absolutely identically, so minor
// systematic differences may occur in addition to the statistical ones.
// (For some MSSM Higgs processes 6.413 has been modified to use
// running quark masses in loops, like 8.3, to allow proper comparison.)
// Subruns  0 -  5 : QCD jets
//          6 - 10 : prompt photons.
//         11 - 12 : t-channel gamma/Z/W exchange.
//         13 - 23 : gamma*/Z^0/W^+-, singly, in pairs or with parton
//         24 - 25 : onia.
//         26 - 30 : top.
//         31 - 40 : Standard Model Higgs.
//         41 - 45 : MSSM Higgses (trivial couplings).
//         46 - 47 : Z' and W'
//         48 - 51 : Left-right-symmetric scenario.
//         52 - 52 : Leptoquark.
//         53 - 55 : Excited fermions (compositeness).
//         56 - 56 : excited Graviton (RS extra dimensions).

#include "Pythia8/Pythia.h"

using namespace Pythia8;

//==========================================================================

int main() {

  // First and last process to test: can run from 0 through 56.
  int iFirst = 0;
  int iLast  = 56;

  // Statistics. Pythia6 run was with 10000, so no point to use more.
  int nEvent = 10000;

  // Normally one subprocess word per subrun, but exceptions exist.
  int nSub[100];
  for (int i = 0; i < 100; ++i) nSub[i] = 1;
  nSub[1] = 3;
  nSub[5] = 3;
  // Starting positions in subprocess words list, recursively defined.
  int iBeg[101] = { 0 };
  for (int i = 0; i < 100; ++i) iBeg[i + 1] = iBeg[i] + nSub[i];
  // List of subprocess words.
  string processes[61] = { "HardQCD:gg2gg", "HardQCD:gg2qqbar",
    "HardQCD:gg2ccbar",  "HardQCD:gg2bbbar","HardQCD:qg2qg" ,
    "HardQCD:qq2qq", "HardQCD:qqbar2gg", "HardQCD:qqbar2qqbarNew",
    "HardQCD:qqbar2ccbar", "HardQCD:qqbar2bbbar", "PromptPhoton:qg2qgamma",
    "PromptPhoton:qqbar2ggamma", "PromptPhoton:gg2ggamma",
    "PromptPhoton:ffbar2gammagamma", "PromptPhoton:gg2gammagamma",
    "WeakBosonExchange:ff2ff(t:gmZ)", "WeakBosonExchange:ff2ff(t:W)",
    "WeakSingleBoson:ffbar2gmZ", "WeakSingleBoson:ffbar2W",
    "WeakDoubleBoson:ffbar2gmZgmZ", "WeakDoubleBoson:ffbar2ZW",
    "WeakDoubleBoson:ffbar2WW", "WeakBosonAndParton:qqbar2gmZg",
    "WeakBosonAndParton:qg2gmZq", "WeakBosonAndParton:ffbar2gmZgm",
    "WeakBosonAndParton:qqbar2Wg", "WeakBosonAndParton:qg2Wq",
    "WeakBosonAndParton:ffbar2Wgm", "Charmonium:all", "Bottomonium:all",
    "Top:gg2ttbar",  "Top:qqbar2ttbar",  "Top:qq2tq(t:W)",
    "Top:ffbar2ttbar(s:gmZ)", "Top:ffbar2tqbar(s:W)",
    "HiggsSM:ffbar2H", "HiggsSM:gg2H", "HiggsSM:ffbar2HZ",
    "HiggsSM:ffbar2HW", "HiggsSM:ff2Hff(t:ZZ)", "HiggsSM:ff2Hff(t:WW)",
    "HiggsSM:qg2Hq", "HiggsSM:gg2Hg(l:t)", "HiggsSM:qg2Hq(l:t)",
    "HiggsSM:qqbar2Hg(l:t)", "HiggsBSM:allH1", "HiggsBSM:allH2",
    "HiggsBSM:allA3", "HiggsBSM:allH+-", "HiggsBSM:allHpair",
    "NewGaugeBoson:ffbar2gmZZprime", "NewGaugeBoson:ffbar2Wprime",
    "LeftRightSymmmetry:ffbar2ZR", "LeftRightSymmmetry:ffbar2WR",
    "LeftRightSymmmetry:ffbar2HLHL", "LeftRightSymmmetry:ffbar2HRHR",
    "LeptoQuark:all", "ExcitedFermion:dg2dStar",
    "ExcitedFermion:qq2dStarq", "ExcitedFermion:qqbar2eStare",
    "ExtraDimensionsG*:all" };

  // List of cross sections from Pythia6.
  double sigma6[57] = {   4.960e-01, 1.627e-02, 2.790e-01, 2.800e-02,
    3.310e-04, 3.653e-04, 1.697e-04, 1.163e-05, 1.065e-07, 8.259e-08,
    8.237e-08, 2.544e-05, 5.321e-06, 5.571e-05, 1.621e-04, 9.039e-09,
    2.247e-08, 5.893e-08, 3.781e-06, 1.078e-05, 4.551e-08, 1.025e-05,
    3.208e-05, 5.435e-08, 1.038e-04, 3.929e-05, 4.155e-07, 6.685e-08,
    1.898e-07, 4.240e-10, 7.142e-09, 1.547e-10, 7.064e-09, 1.316e-10,
    2.332e-10, 5.105e-10, 1.316e-09, 4.462e-11, 5.557e-09, 1.966e-09,
    8.725e-12, 2.450e-08, 5.839e-09, 1.687e-08, 8.950e-11, 4.188e-11,
    1.980e-07, 4.551e-07, 6.005e-09, 1.102e-07, 7.784e-11, 3.488e-11,
    6.006e-08, 3.235e-06, 1.689e-05, 5.986e-07, 3.241e-10 };

  // Generator.
  Pythia pythia;

  // Standard set of masses for comparison with Fortran code.
  pythia.readString("5:m0  = 4.2");
  pythia.readString("6:m0  = 175.");
  pythia.readString("23:m0 = 91.2");
  pythia.readString("24:m0 = 80.");

  // Same kinematics cuts as Fortran code.
  pythia.readString("PhaseSpace:pTHatMin = 20.");
  pythia.readString("6:mMin = 20.");
  pythia.readString("23:mMin = 20.");
  pythia.readString("24:mMin = 20.");
  pythia.readString("25:mMin = 20.");
  pythia.readString("32:mMin = 400.");
  pythia.readString("34:mMin = 400.");
  pythia.readString("42:mMin = 50.");
  pythia.readString("5000039:mMin = 50.");

  // Also same renormalization and factorization scale.
  pythia.readString("SigmaProcess:renormScale2 = 3");
  pythia.readString("SigmaProcess:factorScale2 = 3");

  // Switch off unnecessary parts.
  pythia.readString("PartonLevel:all = off");
  pythia.readString("ProcessLevel:resonanceDecays = off");

  // No printing of settings, particle data or events.
  pythia.readString("Init:showProcesses = off");
  pythia.readString("Init:showChangedSettings = off");
  pythia.readString("Init:showChangedParticleData = off");
  pythia.readString("Next:numberCount = 0");
  pythia.readString("Next:numberShowInfo = 0");
  pythia.readString("Next:numberShowProcess = 0");
  pythia.readString("Next:numberShowEvent = 0");

  // Debug: show information on cross section maximum and violation.
  //pythia.readString("PhaseSpace:showSearch = on");
  //pythia.readString("PhaseSpace:showViolation = on");

  // Loop over processes.
  for (int iProc = iFirst; iProc <= iLast; ++iProc) {
    cout << "\n Begin subrun number " << iProc << " : ";

    // Switch off previous process(es) and switch on new one(s).
    if (iProc > iFirst) for (int i = iBeg[iProc - 1]; i < iBeg[iProc]; ++i)
      pythia.readString( processes[i] + " = off" );
    for (int i = iBeg[iProc]; i < iBeg[iProc + 1]; ++i) {
      pythia.readString( processes[i] + " = on" );
      if (i > iBeg[iProc]) cout << " + ";
      cout << processes[i];
    }
    cout << endl;

    // Switch between SM and MSSM Higgs scenario.
    if (iProc <= 40) {
      pythia.readString("Higgs:useBSM = off");
      pythia.readString("25:m0 = 200.");
    } else {
      pythia.readString("Higgs:useBSM = on");
      pythia.readString("25:m0 = 115.");
      pythia.readString("35:m0 = 300.");
      pythia.readString("36:m0 = 300.");
      pythia.readString("37:m0 = 320.");
      // With default option Higgs:clipWings = on need to reset mass range.
      pythia.readString("25:mMin = 50.");
      pythia.readString("25:mMax = 0.");
    }

    // Initialize for LHC.
    pythia.readString("Beams:eCM = 14000.");

    // If Pythia fails to initialize, exit with error.
    if (!pythia.init()) return 1;

    // Debug: show initialized resonance data first time around.
    //if (iProc == iFirst) pythia.particleData.listChanged(true);

    // Generate events to get cross section statistics.
    for (int iEvent = 0; iEvent < nEvent; ++iEvent) pythia.next();

    // Show statistics.
    //pythia.stat();
    double sigma = pythia.info.sigmaGen();
    cout << " Cross section is " << scientific << setprecision(3)
         << sigma << " and in Pythia6 was " << sigma6[iProc]
         << ",\n i.e. now is factor >>> " << fixed
         << sigma / sigma6[iProc] << " <<< different" <<endl;

  // End of loop over processes.
  }

  // Done.
  return 0;
}
