1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/Beam.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5#include "Rivet/Projections/DecayedParticles.hh"
  6
  7namespace Rivet {
  8
  9
 10  /// @brief J/psi -> gamma KS0 KS0 pi0
 11  class BESIII_2023_I2155157 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2155157);
 16
 17
 18    /// @name Analysis methods
 19    /// @{
 20
 21    /// Book histograms and initialise projections before the run
 22    void init() {
 23      // Initialise and register projections
 24      UnstableParticles ufs = UnstableParticles(Cuts::abspid==443);
 25      declare(ufs, "UFS");
 26      DecayedParticles PSI(ufs);
 27      PSI.addStable(PID::K0S);
 28      PSI.addStable(PID::ETA);
 29      PSI.addStable(PID::PI0);
 30      declare(PSI, "PSI");
 31      declare(Beam(), "Beams");
 32      // Book histograms
 33      for (unsigned int ix=0; ix<7; ++ix) {
 34      	book(_h[ix], 1, 1, 1+ix);
 35      }
 36    }
 37
 38    // angle cuts due regions of BES calorimeter
 39    bool vetoPhoton(const double & cTheta) {
 40      return cTheta>0.92 || (cTheta>0.8 && cTheta<0.86);
 41    }
 42
 43    /// Perform the per-event analysis
 44    void analyze(const Event& event) {
 45      // get the axis, direction of incoming electron
 46      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 47      Vector3 axis;
 48      if (beams.first.pid()>0) {
 49      	axis = beams.first .mom().p3().unit();
 50      }
 51      else {
 52      	axis = beams.second.mom().p3().unit();
 53      }
 54      // find the J/psi decays
 55      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
 56      if ( PSI.decaying().size()!=1) vetoEvent;
 57      if (!PSI.modeMatches(0,4,mode)) vetoEvent;
 58      const Particle & pi0 = PSI.decayProducts()[0].at(111)[0];
 59      const Particles& K0  = PSI.decayProducts()[0].at(310);
 60      const Particle & gam = PSI.decayProducts()[0].at( 22)[0];
 61      double cTheta = axis.dot(gam.p3().unit());
 62      // photon angle cut
 63      if (vetoPhoton(abs(cTheta))) vetoEvent;
 64      // gamma pi omega mass cut
 65      if (abs((pi0.mom()+gam.mom()).mass()-0.78266)<0.04) vetoEvent;
 66      double mKKpi = (K0[0].mom()+K0[1].mom()+pi0.mom()).mass();
 67      if (mKKpi>1.6) vetoEvent;
 68      _h[0]->fill(mKKpi);
 69      _h[1]->fill((K0[0].mom()+K0[1].mom()).mass());
 70      _h[1]->fill((K0[0].mom()+pi0  .mom()).mass());
 71      _h[2]->fill((K0[1].mom()+pi0  .mom()).mass());
 72      _h[3]->fill(cTheta);
 73      // remaining angles
 74      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].mom().betaVec());
 75      FourMomentum pGamma    = boost1.transform(gam.mom());
 76      FourMomentum pHadron = boost1.transform(K0[0].mom()+K0[1].mom()+pi0.mom());
 77      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pHadron.betaVec());
 78      Vector3 axis1 = pGamma.p3().unit();
 79      Vector3 axis2 = boost2.transform(boost1.transform(pi0.mom())).p3().unit();
 80      for (unsigned int ix=0; ix<2; ++ix) {
 81        axis2 = boost2.transform(boost1.transform(K0[ix].mom())).p3().unit();
 82        _h[4]->fill(axis1.dot(axis2));
 83      }
 84      _h[5]->fill(axis1.dot(axis2));
 85      FourMomentum pKK = boost2.transform(boost1.transform(K0[0].mom()+K0[1].mom()));
 86      axis2=pKK.p3().unit();
 87      LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pKK.betaVec());
 88      for (unsigned ix=0; ix<2; ++ix) {
 89        Vector3 axis3 = boost3.transform(boost2.transform(boost1.transform(K0[ix].mom()))).p3().unit();
 90        _h[6]->fill(axis3.dot(axis2));
 91      }
 92    }
 93
 94
 95    /// Normalise histograms etc., after the run
 96    void finalize() {
 97     	normalize(_h, 1.0, false);
 98    }
 99
100    /// @}
101
102
103    /// @name Histograms
104    /// @{
105    Histo1DPtr _h[7];
106    const map<PdgId,unsigned int> mode = { { 111,1}, { 310,2},{ 22,1}};
107    /// @}
108
109
110  };
111
112
113  RIVET_DECLARE_PLUGIN(BESIII_2023_I2155157);
114
115}