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SND_2006_I717778

Cross section for $e^+e^-\to\eta\gamma$ for energies between 600 MeV and 1380 MeV
Experiment: SND (VEPP-2M)
Inspire ID: 717778
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D74 (2006) 014016
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+ e- to hadrons below 0.6 and 1.38 GeV

Cross section for $e^+e^-\to\eta\gamma$ for energies between 600 MeV and 1380 MeV

Source code: SND_2006_I717778.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief Add a short analysis description here
 10  class SND_2006_I717778 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2006_I717778);
 15
 16
 17    /// @name Analysis methods
 18    //@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      // Initialise and register projections
 23      declare(FinalState(), "FS");
 24      declare(UnstableParticles(), "UFS");
 25      book(_numEtaGamma, "TMP/EtaGamma");
 26    }
 27
 28    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 29      for (const Particle &child : p.children()) {
 30	if(child.children().empty()) {
 31	  --nRes[child.pid()];
 32	  --ncount;
 33	}
 34	else
 35	  findChildren(child,nRes,ncount);
 36      }
 37    }
 38
 39    /// Perform the per-event analysis
 40    void analyze(const Event& event) {
 41
 42      const FinalState& fs = apply<FinalState>(event, "FS");
 43
 44      map<long,int> nCount;
 45      int ntotal(0);
 46      for (const Particle& p : fs.particles()) {
 47	nCount[p.pid()] += 1;
 48	++ntotal;
 49      }
 50	 
 51      const FinalState& ufs = apply<FinalState>(event, "UFS");
 52      for (const Particle& p : ufs.particles()) {
 53	if(p.children().empty()) continue;
 54	// find the omega
 55	if(p.pid()==221) {
 56	  map<long,int> nRes = nCount;
 57	  int ncount = ntotal;
 58	  findChildren(p,nRes,ncount);
 59	  // eta pi+pi-
 60	  if(ncount!=1) continue;
 61	  bool matched = true;
 62	  for(auto const & val : nRes) {
 63	    if(val.first==22) {
 64	      if(val.second !=1) {
 65		matched = false;
 66		break;
 67	      }
 68	    }
 69	    else if(val.second!=0) {
 70	      matched = false;
 71	      break;
 72	    }
 73	  }
 74	  if(matched)
 75	    _numEtaGamma->fill();
 76	}
 77      }
 78    }
 79
 80
 81    /// Normalise histograms etc., after the run
 82    void finalize() {
 83
 84      double sigma = _numEtaGamma->val();
 85      double error = _numEtaGamma->err();
 86      sigma *= crossSection()/ sumOfWeights() /nanobarn;
 87      error *= crossSection()/ sumOfWeights() /nanobarn;
 88      for(unsigned int ix=1;ix<3;++ix) {
 89	Scatter2D temphisto(refData(ix, 1, 1));
 90	Scatter2DPtr mult;
 91	book(mult, ix, 1, 1);
 92	for (size_t b = 0; b < temphisto.numPoints(); b++) {
 93	  const double x  = temphisto.point(b).x();
 94	  pair<double,double> ex = temphisto.point(b).xErrs();
 95	  pair<double,double> ex2 = ex;
 96	  if(ex2.first ==0.) ex2. first=0.0001;
 97	  if(ex2.second==0.) ex2.second=0.0001;
 98	  if (inRange(sqrtS()/MeV, x-ex2.first, x+ex2.second)) {
 99	    mult->addPoint(x, sigma, ex, make_pair(error,error));
100	  }
101	  else {
102	    mult->addPoint(x, 0., ex, make_pair(0.,.0));
103	  }
104	}
105      }
106    }
107    
108    //@}
109
110    /// @name Histograms
111    //@{
112    CounterPtr _numEtaGamma;
113    //@}
114
115
116  };
117
118
119  // The hook for the plugin system
120  RIVET_DECLARE_PLUGIN(SND_2006_I717778);
121
122
123}