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CMD3_2019_I1740541

Cross section for $e^+e^-\to\phi\eta$ for energies below 2 GeV
Experiment: CMD3 (VEPP-2M)
Inspire ID: 1740541
Status: VALIDATED
Authors:
  • Peter Richardson
References: Beams: e+ e-
Beam energies: ANY
Run details:
  • e+ e- to hadrons

Measurement of the cross section for $e^+e^-\to K^+K^-\eta$, which is found to be saturated by the resonant $\phi\eta$ sub-process, and therefore only the cross section for $e^+e^-\to\phi\eta$ for energies below 2 GeV is extracted by the CMD3 experiment

Source code: CMD3_2019_I1740541.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 phi eta cross section
 10  class CMD3_2019_I1740541 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(CMD3_2019_I1740541);
 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(_c_phi, "/TMP/phi");
 27    }
 28
 29    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 30      for(const Particle &child : p.children()) {
 31	if(child.children().empty()) {
 32	  --nRes[child.pid()];
 33	  --ncount;
 34	}
 35	else
 36	  findChildren(child,nRes,ncount);
 37      }
 38    }
 39
 40    /// Perform the per-event analysis
 41    void analyze(const Event& event) {
 42      
 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(Cuts::pid==221)) {
 53	if(p.children().empty()) continue;
 54	map<long,int> nRes = nCount;
 55	int ncount = ntotal;
 56	findChildren(p,nRes,ncount);
 57	bool matched = false;
 58	for (const Particle& p2 : ufs.particles(Cuts::pid==333)) {
 59	  map<long,int> nResB = nRes;
 60	  int ncountB = ncount;
 61	  findChildren(p2,nResB,ncountB);
 62	  if(ncountB!=0) continue;
 63	  bool matched = true;
 64	  for(auto const & val : nResB) {
 65	    if(val.second!=0) {
 66	      matched = false;
 67	      break;
 68	    }
 69	  }
 70	  if(matched) {
 71	    _c_phi->fill();
 72	    break;
 73	  }
 74	}
 75	if(matched) break;
 76      }
 77    }
 78
 79
 80    /// Normalise histograms etc., after the run
 81    void finalize() {
 82      double fact = crossSection()/nanobarn/sumOfWeights();
 83      double sigma = _c_phi->val()*fact;
 84      double error = _c_phi->err()*fact;
 85      for(unsigned int ix=1;ix<4;++ix) {
 86	Scatter2D temphisto(refData(ix, 1, 6));
 87	Scatter2DPtr  mult;
 88	book(mult, ix, 1, 6);
 89	for (size_t b = 0; b < temphisto.numPoints(); b++) {
 90	  const double x  = temphisto.point(b).x();
 91	  pair<double,double> ex = temphisto.point(b).xErrs();
 92	  pair<double,double> ex2 = ex;
 93	  if(ex2.first ==0.) ex2. first=0.0001;
 94	  if(ex2.second==0.) ex2.second=0.0001;
 95	  if (inRange(sqrtS()/GeV, x-ex2.first, x+ex2.second)) {
 96	    mult->addPoint(x, sigma, ex, make_pair(error,error));
 97	  }
 98	  else {
 99	    mult->addPoint(x, 0., ex, make_pair(0.,.0));
100	  }
101	}
102      }
103    }
104    
105    //@}
106
107
108    /// @name Histograms
109    //@{
110    CounterPtr _c_phi;
111    //@}
112
113
114  };
115
116
117  // The hook for the plugin system
118  RIVET_DECLARE_PLUGIN(CMD3_2019_I1740541);
119
120
121}