Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief e+e- > eta pi0 gamma
  class SND_2020_I1800477 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2020_I1800477);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_c_omega, "/TMP/omega", refData(1, 1, 1));
      book(_c_total, "/TMP/total", refData(3, 1, 1));
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          --nRes[child.pid()];
          --ncount;
        }
        else
          findChildren(child, nRes, ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {

      const FinalState& fs = apply<FinalState>(event, "FS");

      map<long, int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        // find the eta
        if (p.pid() != 221) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        // check eta pi0 gamma FS
        if (ncount != 2) continue;
        bool matched = true;
        for (const auto& val : nRes) {
          if (abs(val.first) == 22 || val.first == 111) {
            if (val.second != 1) {
              matched = false;
              break;
            }
          }
          else if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (!matched) continue;
        _c_total->fill(sqrtS());
        // check if from omega
        for (const Particle& p2 : ufs.particles()) {
          if (p2.pid() != 223) continue;
          map<long, int> nResB = nRes;
          int ncountB = ncount;
          findChildren(p2, nResB, ncountB);
          if (ncountB != 0) continue;
          bool matched2 = true;
          for (const auto& val : nResB) {
            if (val.second != 0) {
              matched2 = false;
              break;
            }
          }
          if (matched2) _c_omega->fill(sqrtS());
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / picobarn / sumOfWeights();
      scale(_c_total, fact);
      Estimate1DPtr mult;
      book(mult, 1, 1, 1);
      barchart(_c_total, mult);
      scale(_c_omega, fact);
      book(mult, 3, 1, 1);
      barchart(_c_omega, mult);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _c_total, _c_omega;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(SND_2020_I1800477);

}