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 (const auto& 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);

}