Rivet analyses

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

namespace Rivet {


  /// @brief e+e- > rho+ rho-
  class BABAR_2008_I789011 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2008_I789011);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(Cuts::abspid==213), "UFS");
      declare(FinalState(), "FS");
      // histos
      for(unsigned int ix=0;ix<5;++ix)
    book(_h[ix],1,1,1+ix);
    }

    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) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if(beams.first.pid()>0)
    axis = beams.first .momentum().p3().unit();
      else
    axis = beams.second.momentum().p3().unit();
      // types of final state particles
      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;
      }
      // loop over rho mesons
      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
      Particle rhoP,rhoM;
      bool matched(false);
      for (const Particle& p :  ufs.particles()) {
    if(p.children().empty()) continue;
    map<long,int> nRes=nCount;
    int ncount = ntotal;
    findChildren(p,nRes,ncount);
    matched=false;
    // check for antiparticle
    for (const Particle& p2 :  ufs.particles(Cuts::pid==-p.pid())) {
      if(p2.children().empty()) continue;
      map<long,int> nRes2=nRes;
      int ncount2 = ncount;
      findChildren(p2,nRes2,ncount2);
      if(ncount2==0) {
        matched = true;
        for(auto const & val : nRes2) {
          if(val.second!=0) {
        matched = false;
        break;
          }
        }
        // found rho+/-
        if(matched) {
          if(p.pid()>0) {
        rhoP = p;
        rhoM = p2;
          }
          else {
        rhoP = p2;
        rhoM = p;
          } 
          break;
        }
      }
    }
    if(matched) break;
      }
      if(!matched) vetoEvent;
      Particle piP,piM;
      matched = false;
      if (rhoP.children().size()!=2) vetoEvent;
      if (rhoM.children().size()!=2) vetoEvent;
      if(rhoP.children()[0].pid()==211 &&
     rhoP.children()[1].pid()==111)
    piP = rhoP.children()[0];
      else if(rhoP.children()[1].pid()==211 &&
          rhoP.children()[0].pid()==111)
    piP = rhoP.children()[1];
      else
    vetoEvent;
      if(rhoM.children()[0].pid()==-211 &&
     rhoM.children()[1].pid()==111)
    piM = rhoM.children()[0];
      else if(rhoM.children()[1].pid()==-211 &&
          rhoM.children()[0].pid()==111)
    piM = rhoM.children()[1];
      else
    vetoEvent;
      // boost to the rho+ rest frame
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(rhoP.momentum().betaVec());
      Vector3 e1z = rhoP.momentum().p3().unit();
      Vector3 e1y = e1z.cross(axis).unit();
      Vector3 e1x = e1y.cross(e1z).unit();
      Vector3 axis1 = boost1.transform(piP.momentum()).p3().unit();
      double n1x(e1x.dot(axis1)),n1y(e1y.dot(axis1)),n1z(e1z.dot(axis1));
      _h[0]->fill(n1z);
      _h[2]->fill(atan2(n1y,n1x));
      // boost to the rho- frame
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(rhoM.momentum().betaVec());
      Vector3 axis2 = boost2.transform(piM.momentum()).p3().unit();
      double n2x(e1x.dot(axis2)),n2y(e1y.dot(axis2)),n2z(e1z.dot(axis2));
      _h[1]->fill(n2z);
      _h[3]->fill(atan2(n2y,n2x));
      _h[4]->fill(axis.dot(rhoP.momentum().p3().unit()));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0;ix<5;++ix)
    normalize(_h[ix],1.,false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[5];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BABAR_2008_I789011);

}