Rivet analyses

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

namespace Rivet {


  /// @brief e+e- -> Ds(*) D_s1
  class BESIII_2020_I1795949 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1795949);


    /// @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, 1, 1, 1);
      book(_c_DsStar, 2, 1, 1);
      for (const string& en : _c_Ds.binning().edges<0>()) {
        const double eval = stod(en);
        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");
      // 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 == 433 or Cuts::abspid == 20433);
      for (size_t 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;
        // loop over the other fs particles
        for (size_t 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 (const auto& val : nRes2) {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            if ((id1 == 431 && id2 == 20433) || (id1 == 20433 && id2 == 421)) {
              _c_Ds->fill(_sqs);
            }
            else if ((id1 == 433 && id2 == 20433) || (id1 == 20433 && id2 == 433)) {
              _c_DsStar->fill(_sqs);
            }
            break;
          }
        }
        if (matched) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / sumOfWeights() / picobarn;
      scale(_c_Ds, fact);
      scale(_c_DsStar, fact);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _c_Ds, _c_DsStar;
    string _sqs = "";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1795949);

}