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SND_2018_I1638368

Cross section for $e^+e^-\to\eta\pi^+\pi^-$ between 1.08 and 2 GeV
Experiment: SND (VEPP-2M)
Inspire ID: 1638368
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D97 (2018) no.1, 012008
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Source code: SND_2018_I1638368.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_2018_I1638368 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2018_I1638368);
 15
 16
 17    /// @name Analysis methods
 18    //@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22
 23      // Initialise and register projections
 24      declare(FinalState(), "FS");
 25      declare(UnstableParticles(), "UFS");
 26      book(_numEtaPiPi, "TMP/EtaPiPi");
 27    }
 28
 29
 30    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 31      for (const Particle &child : p.children()) {
 32	if(child.children().empty()) {
 33	  --nRes[child.pid()];
 34	  --ncount;
 35	}
 36	else
 37	  findChildren(child,nRes,ncount);
 38      }
 39    }
 40
 41    /// Perform the per-event analysis
 42    void analyze(const Event& event) {
 43      const FinalState& fs = apply<FinalState>(event, "FS");
 44
 45      map<long,int> nCount;
 46      int ntotal(0);
 47      for (const Particle& p : fs.particles()) {
 48	nCount[p.pid()] += 1;
 49	++ntotal;
 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!=2) continue;
 61	  bool matched = true;
 62	  for(auto const & val : nRes) {
 63	    if(abs(val.first)==211) {
 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	    _numEtaPiPi->fill();
 76	}
 77      }
 78    }
 79
 80
 81    /// Normalise histograms etc., after the run
 82    void finalize() {
 83      double sigma = _numEtaPiPi->val();
 84      double error = _numEtaPiPi->err();
 85      sigma *= crossSection()/ sumOfWeights() /nanobarn;
 86      error *= crossSection()/ sumOfWeights() /nanobarn; 
 87      Scatter2D temphisto(refData(1, 1, 1));
 88      Scatter2DPtr mult;
 89      book(mult, 1, 1, 1);
 90      for (size_t b = 0; b < temphisto.numPoints(); b++) {
 91	const double x  = temphisto.point(b).x();
 92	pair<double,double> ex = temphisto.point(b).xErrs();
 93	pair<double,double> ex2 = ex;
 94	if(ex2.first ==0.) ex2. first=0.0001;
 95	if(ex2.second==0.) ex2.second=0.0001;
 96	if (inRange(sqrtS()/GeV, x-ex2.first, x+ex2.second)) {
 97	  mult->addPoint(x, sigma, ex, make_pair(error,error));
 98	}
 99	else {
100	  mult->addPoint(x, 0., ex, make_pair(0.,.0));
101	}
102      }
103    }
104
105    //@}
106
107
108    /// @name Histograms
109    //@{
110    CounterPtr _numEtaPiPi;
111    //@}
112
113
114  };
115
116
117  // The hook for the plugin system
118  RIVET_DECLARE_PLUGIN(SND_2018_I1638368);
119
120
121}