Rivet analyses

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

namespace Rivet {


  /// @brief e+e- -> Ds D_s2
  class BELLE_2020_I1789775 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2020_I1789775);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_c_Ds    ,"/TMP/c_Ds"    );
    }

    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
      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");
      // total analyse final state
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      // unstable charm analysis
      Particles ds = apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==431 or Cuts::abspid==435);
      for(unsigned int ix=0;ix<ds.size();++ix) {
    const Particle& p1 = ds[ix];
        int id1 = abs(p1.pid());
    // check fs
    bool fs = true;
    for (const Particle & child : p1.children()) {
      if(child.pid()==p1.pid()) {
        fs = false;
        break;
      }
    }
        if(!fs) continue;
        // find the children
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p1,nRes,ncount);
        bool matched=false;
        int sign = p1.pid()/id1;
        for(unsigned int iy=ix+1;iy<ds.size();++iy) {
          const Particle& p2 = ds[iy];
          fs = true;
          for (const Particle & child : p2.children()) {
            if(child.pid()==p2.pid()) {
              fs = false;
              break;
            }
          }
          if(!fs) continue;
          if(p2.pid()/abs(p2.pid())==sign) continue;
      int id2 = abs(p2.pid());
      if(!p2.parents().empty() && p2.parents()[0].pid()==p1.pid())
        continue;
      map<long,int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2,nRes2,ncount2);
      if(ncount2!=0) continue;
      matched=true;
      for(auto const & val : nRes2) {
        if(val.second!=0) {
          matched = false;
          break;
        }
      }
      if(matched) {
            if((id1==431 && id2==435) || (id1==435 && id2==431)) {
          Particle Ds2 = id1==435 ? p1 : p2;
          matched = false;
          if(Ds2.children().size()!=2) continue;
          if(Ds2.pid()==435 &&
         ((Ds2.children()[0].pid()==421 && Ds2.children()[1].pid()==321) ||
          (Ds2.children()[1].pid()==421 && Ds2.children()[0].pid()==321) ))
        matched = true;
          else if (Ds2.pid()==-435 &&
         ((Ds2.children()[0].pid()==-421 && Ds2.children()[1].pid()==-321) ||
          (Ds2.children()[1].pid()==-421 && Ds2.children()[0].pid()==-321) ))
        matched = true;
          if(matched) {
        _c_Ds->fill();
        break;
          }
        }
      }
    }
    if(matched) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection()/ sumOfWeights()/picobarn;
      double sigma = _c_Ds->val()*fact;
      double error = _c_Ds->err()*fact;
      Estimate1DPtr mult;
      book(mult, 1, 1, 1);
      for (auto& b : mult->bins()) {
        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
          b.set(sigma, error);
        }
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    CounterPtr _c_Ds;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BELLE_2020_I1789775);

}