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 p pbar
 11  class BESIII_2012_I1079921 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1079921);
 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 or
 25						Cuts::abspid==100443);
 26      declare(ufs, "UFS");
 27      DecayedParticles PSI(ufs);
 28      declare(PSI, "PSI");
 29      declare(Beam(), "Beams");
 30      // book histos
 31      if (isCompatibleWithSqrtS(3.1,0.001)) {
 32	for(unsigned int ix=0;ix<4;++ix)
 33	  book(_h[ix],1,1,1+ix);
 34      }
 35      else if(isCompatibleWithSqrtS(3.686,0.001)) {
 36	book(_h[0],2,1,1);
 37      }
 38      else {
 39	throw Error("Unexpected sqrtS ! Only 3.1 and 3.686 GeV are supported");
 40      }
 41    }
 42
 43    // angle cuts due regions of BES calorimeter
 44    bool vetoPhoton(const double & cTheta) {
 45      return cTheta>0.92 || (cTheta>0.8 && cTheta<0.86);
 46    }
 47
 48    /// Perform the per-event analysis
 49    void analyze(const Event& event) {
 50      // get the axis, direction of incoming electron
 51      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 52      Vector3 axis;
 53      if(beams.first.pid()>0)
 54	axis = beams.first .momentum().p3().unit();
 55      else
 56	axis = beams.second.momentum().p3().unit();
 57      // find the J/psi decays
 58      static const map<PdgId,unsigned int> & mode = { { 2212,1}, { -2212,1},{ 22,1}};
 59      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
 60      if( PSI.decaying().size()!=1) vetoEvent;
 61      if(sqrtS()>3.2 && PSI.decaying()[0].pid()==443) vetoEvent;
 62      if(!PSI.modeMatches(0,3,mode)) vetoEvent;
 63      const Particle & pp   = PSI.decayProducts()[0].at( 2212)[0];
 64      const Particle & pbar = PSI.decayProducts()[0].at(-2212)[0];
 65      const Particle & gam  = PSI.decayProducts()[0].at(   22)[0];
 66      double mass = (pp.momentum()+pbar.momentum()).mass()-pp.mass()-pbar.mass();
 67      _h[0]->fill(mass);
 68      if(!_h[1] || mass>0.05) return;
 69      double cTheta = axis.dot(gam.p3().unit());
 70      // photon angle
 71      if(vetoPhoton(abs(cTheta))) vetoEvent;
 72      _h[1]->fill(cTheta);
 73      // remaining angles
 74      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
 75      FourMomentum pGamma    = boost1.transform(gam.momentum());
 76      FourMomentum pppbar = boost1.transform(pp.momentum()+pbar.momentum());
 77      Vector3 e1z = pGamma.p3().unit();
 78      Vector3 e1y = e1z.cross(axis).unit();
 79      Vector3 e1x = e1y.cross(e1z).unit();
 80      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pppbar.betaVec());
 81      Vector3 axis2 = boost2.transform(boost1.transform(pp.momentum())).p3().unit();
 82      _h[2]->fill(e1z.dot(axis2));
 83      double phi = atan2(axis2.dot(e1y),axis2.dot(e1x))/M_PI*180.;
 84      _h[3]->fill(phi);
 85    }
 86
 87
 88    /// Normalise histograms etc., after the run
 89    void finalize() {
 90      for(unsigned int ix=0;ix<4;++ix)
 91	if(_h[ix]) normalize(_h[ix],1.,false);
 92    }
 93
 94    /// @}
 95
 96
 97    /// @name Histograms
 98    /// @{
 99    Histo1DPtr _h[4];
100    /// @}
101
102
103  };
104
105
106  RIVET_DECLARE_PLUGIN(BESIII_2012_I1079921);
107
108}