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);

}