## main407

Back to index.

    // main407.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.

    // Authors:
    //            Peter Skands
    //            Thanks to: M di Mauro
    //            for the original template for this example

    // Keywords:
    //            Vincia
    //            Weak showers
    //            LHE file
    //            Dark matter

    // Example showing how to run Vincia's electroweak shower with LHEF input.
    // This requires the LHEF files to contain helicities for the hard partons.
    // In this example, the LHEF file contains dark-matter particles annihilating
    // to electron-positron pairs.

    // Note: emitted weak bosons decay inclusively; it would be up to the user
    // themselves to filter events with decays to specific channels if desired.

    #include "Pythia8/Pythia.h"
    #include "math.h"
    #include <iostream>
    #include <string>

    using namespace std;
    using namespace Pythia8;

    int main() {

      // Generator.
      Pythia pythia;

      // Read Pythia settings from command file.
      pythia.readFile("main407.cmnd");

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

      // Allow for possibility of a few faulty events.
      int nError      = pythia.settings.mode("Main:timesAllowErrors");

      double logxMin = -9.;
      double logxMax = 0.;
      double nBins = 100;
      double DeltaBin = (logxMax-logxMin)/nBins;

      // Histogram particle spectra.
      Hist gamma("gamma spectrum", nBins, logxMin, logxMax);
      Hist electron("e+- spectrum", nBins, logxMin, logxMax);
      Hist proton("p spectrum", nBins, logxMin, logxMax);
      Hist nue("nu_e spectrum", nBins, logxMin, logxMax);
      Hist numu("nu_mu spectrum", nBins, logxMin, logxMax);
      Hist nutau("nu_tau spectrum", nBins, logxMin, logxMax);
      Hist rest("remaining particle spectrum", nBins, logxMin, logxMax);

      // Begin event loop.
      int nEvent = 0;
      int iError = 0;
      while (true) {

        // Generate the next event.
        if (!pythia.next()) {

          // If failure because reached end of file then exit event loop.
          if (pythia.info.atEndOfFile()) break;

          // Otherwise count event failure and continue/exit as necessary.
          cout << "Warning: event " << nEvent << " failed" << endl;
          if (++iError == nError) {
            cout << "Error: too many event failures... exiting" << endl;
            break;
          }

          continue;
        }

        /*
         * Process dependent checks and analysis go here ...
         */

        // Add total number of events attempted.
        ++nEvent;

        // Get DM mass.
        double mDM = pythia.event[1].m();

        // Loop over all particles and select final-state ones for histrograms.
        for (int i = 0; i < pythia.event.size(); ++i) {
          if ( !pythia.event[i].isFinal() ) continue;
          int id       = pythia.event[i].id();
          int idAbs    = pythia.event[i].idAbs();
          double e     = pythia.event[i].e();
          if (e <= 0) continue;
          double logx  = log10(e/mDM);
          // Select photons.
          if (idAbs == 22) gamma.fill(logx);
          // Select electrons (positron equivalent).
          else if (id == -11)  electron.fill(logx);
          // Select protons.
          else if (id == -2212 or idAbs == 2112) proton.fill(logx);
          // Select various neutrinos.
          else if (id == 12) nue.fill(logx);
          else if (id == 14) numu.fill(logx);
          else if (id == 16) nutau.fill(logx);
          else rest.fill(logx);
        }
      }

      //Statistic and histrograms.
      pythia.stat();

      gamma.operator*=(1./nEvent/DeltaBin);
      electron.operator*=(1./nEvent/DeltaBin);
      proton.operator*=(1./nEvent/DeltaBin);
      nue.operator*=(1./nEvent/DeltaBin);
      numu.operator*=(1./nEvent/DeltaBin);
      nutau.operator*=(1./nEvent/DeltaBin);

      // Make tables, including statistical errors (last argument = true).
      gamma.table("main407-gamma.dat", false, true, true);
      electron.table("main407-positron.dat", false, true, true);
      proton.table("main407-antiproton.dat", false, true, true);
      nue.table("main407-nue.dat", false, true, true);
      numu.table("main407-numu.dat", false, true, true);
      nutau.table("main407-nutau.dat", false, true, true);
      rest.table("main407-rest.dat", false, true, true);

      cout << gamma << electron << proton << nue << numu << nutau << rest;

      //Done
      return 0;
    }