Rivet analyses

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

namespace Rivet {


  /// @brief gamma gamma -> pi+pi-pi0
  class ARGUS_1997_I420421 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1997_I420421);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // book histos
      if (inRange(sqrtS() / GeV, 0.8, 2.1)) {
        for (unsigned int ix = 0; ix < 5; ++ix) {
          book(_nMeson[ix], "TMP/nMeson_" + toString(ix + 1));
        }
      }
      else {
        throw Error("Invalid CMS energy for ARGUS_1997_I420421");
      }
    }

    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");
      // find the final-state particles
      map<long, int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      // check the 3 meson final state
      if (ntotal != 3) vetoEvent;
      if (nCount[PID::PI0] == 1 && nCount[PID::PIPLUS] == 1 && nCount[PID::PIMINUS] == 1) {
        _nMeson[0]->fill();
      }
      else
        vetoEvent;
      // now the intermediate states
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      // f0 and f2 mesons and rho
      bool nonRes = true;
      for (const Particle& p :
           ufs.particles(Cuts::pid == 225 || Cuts::pid == 9010221 || Cuts::abspid == 213)) {
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        int sign = p.pid() / p.abspid();
        // id of the pion not from the resonance decay
        int idother = p.abspid() == 213 ? -sign * 211 : 111;
        bool matched = true;
        for (const auto& val : nRes) {
          if (val.first == idother) {
            if (val.second != 1) {
              matched = false;
              break;
            }
          }
          else {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
        }
        if (matched) {
          nonRes = false;
          if (p.abspid() == 213) {
            _nMeson[2]->fill();
          }
          else if (p.pid() == 225) {
            _nMeson[3]->fill();
          }
          else {
            _nMeson[4]->fill();
          }
          break;
        }
      }
      if (nonRes) _nMeson[1]->fill();
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_nMeson, crossSection() / nanobarn / sumOfWeights());
      // loop over tables in paper
      for (unsigned int ix = 0; ix < 5; ++ix) {
        unsigned int iy = 1;
        if (ix == 2)
          iy = 5;
        else if (ix == 3)
          iy = 3;
        Estimate1DPtr mult;
        book(mult, ix + 1, 1, iy);
        for (auto& b : mult->bins()) {
          if (inRange(sqrtS() / MeV, b.xMin(), b.xMax())) {
            b.setVal(_nMeson[ix]->val());
            b.setErr(_nMeson[ix]->err());
          }
        }
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    CounterPtr _nMeson[5];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(ARGUS_1997_I420421);

}