Rivet analyses

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

namespace Rivet {


  /// @brief Cross section for $e^+e^-\to \gamma\chi_{c(0,1,2)}$ at energies between 4.009 and 4.36 GeV
  class BESIII_2015_I1329785 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1329785);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nChi0, 1, 1, 8);
      book(_nChi1, 2, 1, 8);
      book(_nChi2, 3, 1, 8);
      for (const string& en : _nChi0.binning().edges<0>()) {
        const double eval = stod(en) * GeV;
        if (isCompatibleWithSqrtS(eval)) {
          _sqs = en;
          break;
        }
      }
      raiseBeamErrorIf(_sqs.empty());
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) const {
      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(Cuts::pid == 10441 or Cuts::pid == 20443 or Cuts::pid == 445)) {
        if (p.children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        // chi gamma
        if (ncount != 1) continue;
        bool matched = true;
        for (const auto& val : nRes) {
          if (val.first == 22) {
            if (val.second != 1) {
              matched = false;
              break;
            }
          }
          else if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          if (p.pid() == 10441)
            _nChi0->fill(_sqs);
          else if (p.pid() == 20443)
            _nChi1->fill(_sqs);
          else if (p.pid() == 445)
            _nChi2->fill(_sqs);
          break;
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double fact = crossSection() / sumOfWeights() / picobarn;
      scale(_nChi0, fact);
      scale(_nChi1, fact);
      scale(_nChi2, fact);
    }
    /// @}

    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _nChi0, _nChi1, _nChi2;
    string _sqs = "";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2015_I1329785);


}