1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief eta -> 3 pi analysis
  9  class KLOE2_2016_I1416990 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(KLOE2_2016_I1416990);
 14
 15
 16    /// @name Analysis methods
 17    /// @{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21      // Initialise and register projections
 22      declare(UnstableParticles(), "UFS");
 23
 24      // Book histograms
 25      book(_dalitz, 1,1,1);
 26      book(_h_dalitz, {-0.9,-0.8,-0.7,-0.6,-0.5,-0.4,-0.3,-0.2,-0.1,
 27                       0.,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8});
 28      for (unsigned int i=1;i<=_h_dalitz->numBins();++i) {
 29        book(_h_dalitz->bins()[i], 2, 1, i);
 30      }
 31      book(_norm, "TMP/norm");
 32    }
 33
 34    void findDecayProducts(const Particle& mother, unsigned int & nstable,
 35                           Particles &pi0, Particles &pip, Particles &pim) {
 36      for (const Particle & p : mother.children()) {
 37        int id = p.pid();
 38        if (id == PID::PIMINUS ) {
 39          pim.push_back(p);
 40          ++nstable;
 41        }
 42        else if (id == PID::PIPLUS) {
 43          pip.push_back(p);
 44          ++nstable;
 45        }
 46        else if (id == PID::PI0) {
 47          pi0.push_back(p);
 48          ++nstable;
 49        }
 50        else if ( !p.children().empty() ) {
 51          findDecayProducts(p, nstable, pi0,pip,pim);
 52        }
 53        else {
 54          ++nstable;
 55        }
 56      }
 57    }
 58
 59    /// Perform the per-event analysis
 60    void analyze(const Event& event) {
 61      // Loop over eta mesons
 62      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==PID::ETA)) {
 63      	Particles pi0, pip, pim;
 64      	unsigned nstable(0);
 65      	findDecayProducts(p,nstable,pi0,pip,pim);
 66      	if (nstable==3 && pi0.size()==1 && pip.size()==1 && pim.size()==1) {
 67          // massesx
 68      	  double meta = p.mass();
 69      	  double mpip = pip[0].mass();
 70      	  double mpim = pim[0].mass();
 71      	  double mpi0 = pi0[0].mass();
 72          // kinetic energies
 73      	  double Q  = meta-mpip-mpim-mpi0;
 74      	  double Ep = 0.5/meta*(sqr(meta)+sqr(mpip)-(p.momentum()-pip[0].momentum()).mass2())-mpip;
 75      	  double Em = 0.5/meta*(sqr(meta)+sqr(mpim)-(p.momentum()-pim[0].momentum()).mass2())-mpim;
 76      	  double E0 = 0.5/meta*(sqr(meta)+sqr(mpi0)-(p.momentum()-pi0[0].momentum()).mass2())-mpi0;
 77          // X and Y variables
 78      	  double X = sqrt(3.)/Q*(Ep-Em);
 79      	  double Y = 3.*E0/Q-1.;
 80       	  _dalitz->fill(X,Y);
 81          _h_dalitz->fill(Y,X);
 82       	  if(fabs(X)<0.03225806451612903 && Y>0. && Y<0.1) _norm->fill();
 83      	}
 84      }
 85    }
 86
 87
 88    /// Normalise histograms etc., after the run
 89    void finalize() {
 90      scale(_dalitz, 0.06451612903225806*0.1/ *_norm);
 91      scale(_h_dalitz, 0.06451612903225806/ *_norm);
 92    }
 93
 94    /// @}
 95
 96
 97    /// @name Histograms
 98    /// @{
 99    Histo2DPtr _dalitz;
100    Histo1DGroupPtr _h_dalitz;
101    CounterPtr _norm;
102    /// @}
103
104
105  };
106
107
108  RIVET_DECLARE_PLUGIN(KLOE2_2016_I1416990);
109
110
111}