## main328

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    // main328.cc is a part of the PYTHIA event generator.
    // Copyright (C) 2025 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:
    //            Total cross section
    //            Partial cross sections

    // Authors:
    //            Torbjörn Sjostrand

    // Study total, elastic and diffractive cross sections in several models.
    // Most only available for pp and p pbar; and RPP only for total and elastic.
    // ABMST has been modified for diffraction, see html manual for details.

    // Note: This main program circumvents the need to generate loads of events
    // to just output total cross sections, by creating a free standing object
    // of type SigmaTotal, and copy relevant information from the Pythia object.
    // See main486.cc for example how to use the public cross section methods.

    #include "Pythia8/Pythia.h"
    #include "Pythia8/SigmaTotal.h"

    using namespace Pythia8;

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

    int main() {

      // Basic parameters and histogram binning.
      int idA = 2212;
      int idB = 2212;
      double eCMmin = 10.;
      double eCMmax = 100000.;
      int nECM = 40;

      // Histograms.
      Hist sigTot[5], sigEl[5], sigND[5], sigSD[5], sigDD[5], sigCD[5];
      for (int i = 0; i < 5; ++i) {
        sigTot[i].book("Total cross section",       nECM, eCMmin, eCMmax, true);
        sigEl[i].book("Elastic cross section",      nECM, eCMmin, eCMmax, true);
        sigND[i].book("Non-diff cross section",     nECM, eCMmin, eCMmax, true);
        sigSD[i].book("Single diff cross section",  nECM, eCMmin, eCMmax, true);
        sigDD[i].book("Double diff cross section",  nECM, eCMmin, eCMmax, true);
        sigCD[i].book("Central diff cross section", nECM, eCMmin, eCMmax, true);
      }
      double eCM, sigT,sigE, sigN, sigS, sigD, sigC;

      // Loop over parametrizations.
      for (int iSig = 0; iSig < 4; ++iSig) {
        int modeSig = iSig + 1;

        // A SigmaTotal object, which will be used to calculate the cross
        // sections.
        SigmaTotal st;
        // Generator. Cross section model choice.
        Pythia pythia;
        pythia.settings.mode("Beams:idA", idA);
        pythia.settings.mode("Beams:idB", idB);
        pythia.settings.mode("SigmaTotal:mode", modeSig);
        pythia.settings.mode("SigmaDiffractive:mode", modeSig);

        // Switch off most of event generation and initialize.
        pythia.readString("SoftQCD:elastic = on");
        pythia.readString("PartonLevel:all = off");
        pythia.readString("HadronLevel:all = off");

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

        // Make a copy of the Pythia info object to initialize
        // pointers in SigmaTotal.
        Info pythiaInfo(pythia.info);
        // Initialize the pointers.
        st.initInfoPtr(pythiaInfo);
        // Initialize the SigmaTotal instance.
        st.init();

        // Loop through logarithmic grid of collision energies.
        for (int iECM = 0; iECM < nECM; ++iECM) {
          eCM = eCMmin * pow( eCMmax / eCMmin, (iECM + 0.5) / double(nECM) );

          // Calculate cross sections.
          st.calc( idA, idB, eCM);
          sigT = st.sigmaTot();
          sigE = st.sigmaEl();
          if (iSig < 3) {
            sigN = st.sigmaND();
            sigS = st.sigmaXB() + st.sigmaAX();
            sigD = st.sigmaXX();
            sigC = st.sigmaAXB();
          }

          // Fill histograms.
          sigTot[iSig].fill( eCM, sigT);
          sigEl[iSig].fill(  eCM, sigE);
          if (iSig < 3) {
            sigND[iSig].fill(  eCM, sigN);
            sigSD[iSig].fill(  eCM, sigS);
            sigDD[iSig].fill(  eCM, sigD);
            sigCD[iSig].fill(  eCM, sigC);
          }
        }

      // End loop over parametrizations.
      }

      // Plot histograms.
      HistPlot hpl("plot328");
      hpl.frame("fig328", "Total cross section in pp collisions",
        "$E_{\\mathrm{CM}}$ (GeV)", "$\\sigma$ (mb)", 8.0, 5.4);
      hpl.add( sigTot[0], "-,black", "SaS/DL");
      hpl.add( sigTot[1], "-,red", "MBR");
      hpl.add( sigTot[2], "-,blue", "ABMST");
      hpl.add( sigTot[3], "-,green", "RPP2016");
      hpl.plot();
      hpl.frame("", "Elastic cross section in pp collisions",
        "$E_{\\mathrm{CM}}$ (GeV)", "$\\sigma$ (mb)", 8.0, 5.4);
      hpl.add( sigEl[0], "-,black", "SaS/DL");
      hpl.add( sigEl[1], "-,red", "MBR");
      hpl.add( sigEl[2], "-,blue", "ABMST");
      hpl.add( sigEl[3], "-,green", "RPP2016");
      hpl.plot();
      hpl.frame("", "Nondiffractive cross section in pp collisions",
        "$E_{\\mathrm{CM}}$ (GeV)", "$\\sigma$ (mb)", 8.0, 5.4);
      hpl.add( sigND[0], "-,black", "SaS/DL");
      hpl.add( sigND[1], "-,red", "MBR");
      hpl.add( sigND[2], "-,blue", "ABMST mod");
      hpl.plot();
      hpl.frame("", "Single diffractive cross section in pp collisions",
        "$E_{\\mathrm{CM}}$ (GeV)", "$\\sigma$ (mb)", 8.0, 5.4);
      hpl.add( sigSD[0], "-,black", "SaS/DL");
      hpl.add( sigSD[1], "-,red", "MBR");
      hpl.add( sigSD[2], "-,blue", "ABMST mod");
      hpl.plot();
      hpl.frame("", "Double diffractive cross section in pp collisions",
        "$E_{\\mathrm{CM}}$ (GeV)", "$\\sigma$ (mb)", 8.0, 5.4);
      hpl.add( sigDD[0], "-,black", "SaS/DL");
      hpl.add( sigDD[1], "-,red", "MBR");
      hpl.add( sigDD[2], "-,blue", "ABMST mod");
      hpl.plot();
      hpl.frame("", "Central diffractive cross section in pp collisions",
        "$E_{\\mathrm{CM}}$ (GeV)", "$\\sigma$ (mb)", 8.0, 5.4);
      hpl.add( sigCD[0], "-,black", "SaS/DL");
      hpl.add( sigCD[1], "-,red", "MBR");
      hpl.add( sigCD[2], "-,blue", "ABMST mod");
      hpl.plot();

      // Done.
      return 0;
    }