Rivet analyses

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

namespace Rivet {


  /// @brief Cross section for D0 D- pi+ +c.c
  class BELLE_2008_I759073 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2008_I759073);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nD0, "/TMP/nD0");
    }

    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");

      map<long, int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      const FinalState& ufs = apply<FinalState>(event, "UFS");


      for (unsigned int ix = 0; ix < ufs.particles().size(); ++ix) {
        const Particle& p1 = ufs.particles()[ix];
        if (abs(p1.pid()) != 421) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p1, nRes, ncount);
        bool matched = false;
        int id2 = p1.pid() > 0 ? -411 : 411;
        int ipi = p1.pid() > 0 ? 211 : -211;
        for (unsigned int iy = 0; iy < ufs.particles().size(); ++iy) {
          if (ix == iy) continue;
          const Particle& p2 = ufs.particles()[iy];
          if (p2.pid() != id2) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(p2, nRes2, ncount2);
          if (ncount2 != 1) continue;
          matched = true;
          for (const auto& val : nRes2) {
            if (val.first == ipi) {
              if (val.second != 1) {
                matched = false;
                break;
              }
            }
            else if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) break;
        }
        if (matched) _nD0->fill();
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double sigma = _nD0->val();
      double error = _nD0->err();
      sigma *= crossSection() / sumOfWeights() / nanobarn;
      error *= crossSection() / sumOfWeights() / nanobarn;
      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 _nD0;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2008_I759073);


}