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 JPsi > Lambda, Lambdabar with Lambda -> n gamma
  class BESIII_2022_I2099126 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2099126);


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

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

      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(), "UFS");
      declare(FinalState(), "FS");
      for(unsigned int ix=0;ix<2;++ix) {
    book(_n[ix],"TMP/n_" + toString(ix+1));
    book(_t[ix],"TMP/t_" + toString(ix+1));
    for(unsigned int iy=0;iy<2;++iy) {
      book(_h_mu[ix][iy],1,1,2*ix+iy+1);
    }
      }
      book(_n[2],"TMP/n_3");
      book(_t[2],"TMP/t_3");
    }

    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 lambda0 baryons
      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
      Particle Lambda,LamBar;
      bool matched(false);
      for (const Particle& p :  ufs.particles(Cuts::abspid==3122)) {
        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 baryon and antibaryon
            if(matched) {
          if(p.pid()>0) {
        Lambda = p;
        LamBar = p2;
          }
          else {
        Lambda = p2;
        LamBar = p;
          } 
              break;
            }
          }
        }
        if(matched) break;
      }
      if(!matched) vetoEvent;
      // check the Lambda decay mode
      bool radiative[2]={false,false};
      // identifyt Lambda decay
      Particle baryon1;
      if ( (Lambda.children()[0].pid()==PID::PROTON &&
        Lambda.children()[1].pid()==PID::PIMINUS ) ) {
    radiative[0]=false;
    baryon1 = Lambda.children()[0];
      }
      else if ( (Lambda.children()[1].pid()==PID::PROTON &&
         Lambda.children()[0].pid()==PID::PIMINUS ) ) {
    radiative[0]=false;
    baryon1 = Lambda.children()[1];
      }
      else if ( (Lambda.children()[0].pid()==PID::NEUTRON &&
         Lambda.children()[1].pid()==PID::PHOTON ) ) {
    radiative[0]=true;
    baryon1 = Lambda.children()[0];
      }
      else if ( (Lambda.children()[1].pid()==PID::NEUTRON &&
         Lambda.children()[0].pid()==PID::PHOTON ) ) {
    radiative[0]=true;
    baryon1 = Lambda.children()[1];
      }
      else
    vetoEvent;
      Particle baryon2;
      if ( (LamBar.children()[0].pid()==PID::ANTIPROTON &&
        LamBar.children()[1].pid()==PID::PIPLUS ) ) {
    radiative[1]=false;
    baryon2 = LamBar.children()[0];
      }
      else if ( (LamBar.children()[1].pid()==PID::ANTIPROTON &&
         LamBar.children()[0].pid()==PID::PIPLUS ) ) {
    radiative[1]=false;
    baryon2 = LamBar.children()[1];
      }
      else if ( (LamBar.children()[0].pid()==PID::ANTINEUTRON &&
         LamBar.children()[1].pid()==PID::PHOTON ) ) {
    radiative[1]=true;
    baryon2 = LamBar.children()[0];
      }
      else if ( (LamBar.children()[1].pid()==PID::ANTINEUTRON &&
         LamBar.children()[0].pid()==PID::PHOTON ) ) {
    radiative[1]=true;
    baryon2 = LamBar.children()[1];
      }
      else
    vetoEvent;
      if (radiative[0] == radiative[1]) vetoEvent;
      // boost to the Lambda rest frame
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Lambda.momentum().betaVec());
      Vector3 e1z = Lambda.momentum().p3().unit();
      Vector3 e1y = e1z.cross(axis).unit();
      Vector3 e1x = e1y.cross(e1z).unit();
      Vector3 axis1 = boost1.transform(baryon1.momentum()).p3().unit();
      double n1x(e1x.dot(axis1)),n1y(e1y.dot(axis1)),n1z(e1z.dot(axis1));
      // boost to the Lambda bar
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(LamBar.momentum().betaVec());
      Vector3 axis2 = boost2.transform(baryon2.momentum()).p3().unit();
      double n2x(e1x.dot(axis2)),n2y(e1y.dot(axis2)),n2z(e1z.dot(axis2));
      double cosL = axis.dot(Lambda.momentum().p3().unit());
      double sinL = sqrt(1.-sqr(cosL));
      double T1 = sqr(sinL)*n1x*n2x+sqr(cosL)*n1z*n2z;
      // lambda -> n gamma
      if(radiative[0]) {
    _h_mu[0][0]->fill( cosL,n2y);
    _h_mu[0][1]->fill( cosL,n1y);
    _n[0]->fill();
    _n[2]->fill();
    _t[0]->fill(T1);
    _t[2]->fill(T1);
      }
      // lambdabar -> nbar gamma
      else {
    _h_mu[1][0]->fill( cosL,n1y);
    _h_mu[1][1]->fill( cosL,n2y);
    _n[1]->fill();
    _n[2]->fill();
    _t[1]->fill(T1);
    _t[2]->fill(T1);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // values of constants
      double aPsi  = 0.461;
      double aPlus =-0.758;
      double factor = 45.*(3. +aPsi)/(11. + 5.*aPsi)/aPlus;
      // plots
      for (unsigned int ix=0;ix<2;++ix) {
        for(unsigned int iy=0;iy<2;++iy) {
          scale(_h_mu[ix][iy],10.*0.2/ *_n[ix]);
        }
      }
      // alpha from the moments
      for (unsigned int ix=0;ix<3;++ix) {
        double value = _t[ix]->val()/_n[ix]->val();
        double error = _t[ix]->err()/_n[ix]->val();
        value *= factor;
        error *= abs(factor);
        if(ix==1) value *=-1.;
        Estimate0DPtr  alpha;
        book(alpha,2,1,1+ix);
        alpha->set(value, error);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mu[2][2];
    CounterPtr _n[3];
    Histo1DPtr _h_ctheta[3];
    CounterPtr _t[3];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2099126);

}