Rivet analyses

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

namespace Rivet {


  /// @brief e+e- to pi+pi- J/psi
  class BESIII_2013_I1225275 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2013_I1225275);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(FinalState(), "FS");
      // histograms
      book(_h_sigma, 1, 1, 1);
      for (unsigned int ix = 0; ix < 3; ++ix) {
        book(_h_mass[ix], 2, 1, 1 + ix);
      }
      book(_h_mass[3], 3, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles fs = apply<FinalState>(event, "FS").particles();
      Particles PSI, other;
      for (const Particle& p : fs) {
        Particle parent = p;
        while (!parent.parents().empty()) {
          parent = parent.parents()[0];
          if (parent.abspid() == PID::JPSI) break;
        }
        if (parent.abspid() != PID::JPSI) {
          other.push_back(p);
          continue;
        }
        bool found = false;
        for (auto& p : PSI) {
          // psi already in list
          if (fuzzyEquals(p.mom(), parent.mom())) {
            found = true;
            break;
          }
        }
        if (!found) PSI.push_back(parent);
      }
      // J/psi + 2 other particles
      if (PSI.size() != 1 || other.size() != 2) vetoEvent;
      // other particles pi+ pi-
      if (!(other[0].pid() == -other[1].pid() && other[0].abspid() == PID::PIPLUS)) vetoEvent;
      if (other[0].pid() < 0) swap(other[0], other[1]);
      // cross secrtion
      _h_sigma->fill("4.26"s);
      // fill the mass plots
      double mJpsipi[2] = {(other[0].mom() + PSI[0].mom()).mass(), (other[1].mom() + PSI[0].mom()).mass()};
      for (unsigned int ix = 0; ix < 2; ++ix) {
        _h_mass[ix]->fill(mJpsipi[ix]);
      }
      _h_mass[2]->fill((other[0].mom() + other[1].mom()).mass());
      _h_mass[3]->fill(max(mJpsipi[0], mJpsipi[1]));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_sigma, crossSection() / sumOfWeights() / picobarn);
      normalize(_h_mass, 1.0, false);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _h_sigma;
    Histo1DPtr _h_mass[4];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2013_I1225275);

}