Rivet analyses

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

namespace Rivet {


  /// @brief B(*) bar{B}(*) exclusive cross section
  class BELLE_2021_I1859137 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2021_I1859137);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // histograms
      for (size_t ix = 0; ix < 3; ++ix) {
        book(_sigma[ix], 1, 1, 1 + ix);
      }
      for (const string& en : _sigma[0].binning().edges<0>()) {
        const double eval = std::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()] -= 1;
          --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;
      }
      // extract botton hadrons
      Particles bHadrons = apply<FinalState>(event, "UFS")
                               .particles(Cuts::abspid == 511 or Cuts::abspid == 513 or Cuts::abspid == 521
                                          or Cuts::abspid == 523);
      for (size_t ix = 0; ix < bHadrons.size(); ++ix) {
        long pix = bHadrons[ix].parents()[0].abspid();
        if (pix == 511 || pix == 413 || pix == 521 || pix == 523) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(bHadrons[ix], nRes, ncount);
        bool matched = false;
        for (unsigned int iy = ix + 1; iy < bHadrons.size(); ++iy) {
          long piy = bHadrons[ix].parents()[0].abspid();
          if (piy == 511 || piy == 413 || piy == 521 || piy == 523) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(bHadrons[iy], nRes2, ncount2);
          if (ncount2 != 0) continue;
          matched = true;
          for (const auto& val : nRes2) {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            if (bHadrons[ix].abspid() == 511 || bHadrons[ix].abspid() == 521) {
              if (bHadrons[iy].pid() == -bHadrons[ix].pid())
                _sigma[0]->fill(_sqs);
              else
                _sigma[1]->fill(_sqs);
            }
            else if (bHadrons[ix].abspid() == 513 || bHadrons[ix].abspid() == 523) {
              if (bHadrons[iy].pid() == -bHadrons[ix].pid())
                _sigma[2]->fill(_sqs);
              else
                _sigma[1]->fill(_sqs);
            }
            break;
          }
        }
        if (matched) break;
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_sigma, crossSection() / sumOfWeights() / picobarn);
    }

    ///@}


    /// @name Histograms
    ///@{
    BinnedHistoPtr<string> _sigma[3];
    string _sqs = "";
    ///@}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2021_I1859137);

}