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BESIII_2015_I1377204

Cross section for $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeV
Experiment: BESIII (BEPC)
Inspire ID: 1377204
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.Lett. 115 (2015) 112003, 2015
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Measurement of the cross section for $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeV

Source code: BESIII_2015_I1377204.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 BESIII_2015_I1377204 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1377204);
 15
 16
 17    /// @name Analysis methods
 18    //@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      declare(FinalState(), "FS");
 23      declare(UnstableParticles(), "UFS");
 24      book(_nJPsi, "TMP/jpsi");
 25    }
 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      const FinalState& fs = apply<FinalState>(event, "FS");
 42      map<long,int> nCount;
 43      int ntotal(0);
 44      for (const Particle& p : fs.particles()) {
 45	nCount[p.pid()] += 1;
 46	++ntotal;
 47      }
 48      const FinalState& ufs = apply<FinalState>(event, "UFS");
 49      for (const Particle& p : ufs.particles()) {
 50	if(p.children().empty()) continue;
 51	// find the j/psi
 52	if(p.pid()==443) {
 53	  map<long,int> nRes = nCount;
 54	  int ncount = ntotal;
 55	  findChildren(p,nRes,ncount);
 56	  // J/psi pi0pi0
 57	  if(ncount!=2) continue;
 58	  bool matched = true;
 59	  for(auto const & val : nRes) {
 60	    if(abs(val.first)==111) {
 61	      if(val.second !=2) {
 62		matched = false;
 63		break;
 64	      }
 65	    }
 66	    else if(val.second!=0) {
 67	      matched = false;
 68	      break;
 69	    }
 70	  }
 71	  if(matched) {
 72	    _nJPsi->fill();
 73	    break;
 74	  }
 75	}
 76      }
 77    }
 78
 79
 80    /// Normalise histograms etc., after the run
 81    void finalize() {
 82      double sigma = _nJPsi->val();
 83      double error = _nJPsi->err();
 84      sigma *= crossSection()/ sumOfWeights() /picobarn;
 85      error *= crossSection()/ sumOfWeights() /picobarn; 
 86      Scatter2D temphisto(refData(1, 1, 12));
 87      Scatter2DPtr  mult;
 88      book(mult, 1, 1, 12);
 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    /// @name Histograms
108    //@{
109    CounterPtr _nJPsi;
110    //@}
111
112
113  };
114
115
116  // The hook for the plugin system
117  RIVET_DECLARE_PLUGIN(BESIII_2015_I1377204);
118
119
120}