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CMD2_1999_I483994

Cross section for $e^+e^-\to2\pi^+2\pi^-$ and $\pi^+\pi^-2\pi^0$ below 1.38 GeV
Experiment: CMD2 (VEPP-2M)
Inspire ID: 483994
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Lett. B466 (1999) 392-402, 199 9
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Measurement of the cross section for $e^+e^-\to2\pi^+2\pi^-$ and $\pi^+\pi^-2\pi^0$ below 1.38 GeV

Source code: CMD2_1999_I483994.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5
  6
  7namespace Rivet {
  8
  9
 10  /// @brief Add a short analysis description here
 11  class CMD2_1999_I483994 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_1999_I483994);
 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      declare(FinalState(), "FS");
 25      declare(UnstableParticles(), "UFS");
 26      book(_ncharged, "TMP/charged");
 27      book(_nneutral, "TMP/neutral");
 28      book(_nomega, "TMP/omega");
 29    }
 30
 31    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 32      for (const Particle &child : p.children()) {
 33	if(child.children().empty()) {
 34	  --nRes[child.pid()];
 35	  --ncount;
 36	}
 37	else
 38	  findChildren(child,nRes,ncount);
 39      }
 40    }
 41
 42    /// Perform the per-event analysis
 43    void analyze(const Event& event) {
 44      const FinalState& fs = apply<FinalState>(event, "FS");
 45      
 46      map<long,int> nCount;
 47      int ntotal(0);
 48      for (const Particle& p : fs.particles()) {
 49	nCount[p.pid()] += 1;
 50	++ntotal;
 51      }
 52      if(ntotal==4) {
 53	if( nCount[211] == 2 && nCount[-211] == 2 )
 54	  _ncharged->fill();
 55	else if( nCount[211] == 1 && nCount[-211] == 1 && nCount[111] == 2)
 56	  _nneutral->fill();
 57      }
 58      
 59
 60      const FinalState& ufs = apply<FinalState>(event, "UFS");
 61      for (const Particle& p : ufs.particles()) {
 62	if(p.children().empty()) continue;
 63	// find the omega
 64	if(p.pid()==223) {
 65	  map<long,int> nRes = nCount;
 66	  int ncount = ntotal;
 67	  findChildren(p,nRes,ncount);
 68	  // omega pi+pi-
 69	  if(ncount!=1) continue;
 70	  bool matched = true;
 71	  for(auto const & val : nRes) {
 72	    if(abs(val.first)==111) {
 73	      if(val.second !=1) {
 74		matched = false;
 75		break;
 76	      }
 77	    }
 78	    else if(val.second!=0) {
 79	      matched = false;
 80	      break;
 81	    }
 82	  }
 83	  if(matched)
 84	    _nomega->fill();
 85	}
 86      }
 87    }
 88
 89
 90    /// Normalise histograms etc., after the run
 91    void finalize() {
 92      for(unsigned int ix=1;ix<4;++ix) {
 93	double sigma = 0., error = 0.;
 94	if(ix==1) {
 95	  sigma = _ncharged->val();
 96	  error = _ncharged->err();
 97	}
 98	else if(ix==2) {
 99   	  sigma = _nneutral->val();
100	  error = _nneutral->err();
101        }
102	else if(ix==3) {
103	  sigma = _nomega->val();
104	  error = _nomega->err();
105	}
106	sigma *= crossSection()/ sumOfWeights() /nanobarn;
107	error *= crossSection()/ sumOfWeights() /nanobarn; 
108	Scatter2D temphisto(refData(ix, 1, 1));
109	Scatter2DPtr mult;
110	book(mult, ix, 1, 1);
111	for (size_t b = 0; b < temphisto.numPoints(); b++) {
112	  const double x  = temphisto.point(b).x();
113	  pair<double,double> ex = temphisto.point(b).xErrs();
114	  pair<double,double> ex2 = ex;
115	  if(ex2.first ==0.) ex2. first=0.0001;
116	  if(ex2.second==0.) ex2.second=0.0001;
117	  if (inRange(sqrtS()/MeV, x-ex2.first, x+ex2.second)) {
118	    mult->addPoint(x, sigma, ex, make_pair(error,error));
119	  }
120	  else {
121	    mult->addPoint(x, 0., ex, make_pair(0.,.0));
122	  }
123	}
124      }
125    }
126
127    //@}
128
129
130    /// @name Histograms
131    //@{
132    CounterPtr _ncharged,_nneutral,_nomega;
133    //@}
134
135
136  };
137
138
139  // The hook for the plugin system
140  RIVET_DECLARE_PLUGIN(CMD2_1999_I483994);
141
142
143}