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);

}