Rivet Analyses Reference

BESIII_2020_I1814783

$e^+e^-\to\Sigma^+\bar{\Sigma}^-$ and $\Sigma^-\bar{\Sigma}^+$ cross sections for centre-of-mass energies between 2.3864 and 3 GeV
Experiment: BESIII (BEPC)
Inspire ID: 1814783
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • arxiv:2009.01404
Beams: e- e+
Beam energies: ANY
Run details:
  • e+ e- to hadrons. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples.

$e^+e^-\to\Sigma^+\bar{\Sigma}^-$ and $\Sigma^-\bar{\Sigma}^+$ cross sections for centre-of-mass energies between 2.3864 and 3 GeV. The angular distribution for $\sqrt{s}=2.396$\,GeV is also measured. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples.

Source code: BESIII_2020_I1814783.cc
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief e+ e- > sigma+- sigmabar -+
  class BESIII_2020_I1814783 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1814783);


    /// @name Analysis methods
    ///@{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_n_plus ,"/TMP/NPLUS" );
      book(_n_minus,"/TMP/NMINUS");
      if(isCompatibleWithSqrtS(2.396, 1E-2)) {
	book(_h_cTheta_A,3,1,1);
	book(_h_cTheta_B,3,1,2);
      }
    }

    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
      for(const Particle &child : p.children()) {
	if(child.children().empty()) {
	  nRes[child.pid()]-=1;
	  --ncount;
	}
	else
	  findChildren(child,nRes,ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");
      // total hadronic and muonic cross sections
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
	nCount[p.pid()] += 1;
	++ntotal;
      }
      // find the Sigmas
      const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
      for(unsigned int ix=0;ix<ufs.particles().size();++ix) {
      	const Particle& p1 = ufs.particles()[ix];
      	if(abs(p1.pid())!=3112&&abs(p1.pid())!=3222) continue;
      	bool matched = false;
       	// check fs
       	bool fs = true;
      	for(const Particle & child : p1.children()) {
      	  if(child.pid()==p1.pid()) {
      	    fs = false;
      	    break;
      	  }
      	}
      	if(!fs) continue;
	// find the children
	map<long,int> nRes = nCount;
	int ncount = ntotal;
	findChildren(p1,nRes,ncount);
	for(unsigned int iy=ix+1;iy<ufs.particles().size();++iy) {
       	  const Particle& p2 = ufs.particles()[iy];
       	  if(p2.pid() != -p1.pid()) continue;
       	  // check fs
      	  bool fs = true;
      	  for(const Particle & child : p2.children()) {
      	    if(child.pid()==p2.pid()) {
      	      fs = false;
      	      break;
      	    }
      	  }
      	  if(!fs) continue;
      	  map<long,int> nRes2 = nRes;
      	  int ncount2 = ncount;
      	  findChildren(p2,nRes2,ncount2);
      	  if(ncount2!=0) continue;
      	  matched=true;
      	  for(auto const & val : nRes2) {
      	    if(val.second!=0) {
      	      matched = false;
      	      break;
      	    }
      	  }
      	  if(matched) {
	    if(abs(p1.pid())==3222) {
	      _n_plus->fill();
	      if(_h_cTheta_A) {
		double cTheta = p1.pid()>0 ?
		  cos(p1.momentum().polarAngle()) :
		  cos(p2.momentum().polarAngle());
		_h_cTheta_A->fill(cTheta);
		_h_cTheta_B->fill(cTheta);
	      }
	    }
	    else if(abs(p1.pid())==3112)
	      _n_minus->fill();
	    break;
	  }
      	}
	if(matched) break;
      }
      
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      if(_h_cTheta_A) {
      	normalize(_h_cTheta_A);
      	normalize(_h_cTheta_B);
      }
      double fact = crossSection()/ sumOfWeights() /picobarn;
      for(unsigned int iy=1;iy<3;++iy) {
	double sigma,error;
	if(iy==1) {
	  sigma = _n_plus->val()*fact;
	  error = _n_plus->err()*fact;
	}
	else {
	  sigma = _n_minus->val()*fact;
	  error = _n_minus->err()*fact;
	}
	for(unsigned int ix=1;ix<3;++ix) {
	  Scatter2D temphisto(refData(ix, 1, iy));
	  Scatter2DPtr  mult;
	  book(mult, ix, 1, iy);
	  for (size_t b = 0; b < temphisto.numPoints(); b++) {
	    const double x  = temphisto.point(b).x();
	    pair<double,double> ex = temphisto.point(b).xErrs();
	    pair<double,double> ex2 = ex;
	    if(ex2.first ==0.) ex2. first=0.0001;
	    if(ex2.second==0.) ex2.second=0.0001;
	    if (inRange(sqrtS()/GeV, x-ex2.first, x+ex2.second)) {
	      mult->addPoint(x, sigma, ex, make_pair(error,error));
	    }
	    else {
	      mult->addPoint(x, 0., ex, make_pair(0.,.0));
	    }
	  }
	}
      }
    }
    ///@}


    /// @name Histograms
    ///@{
    CounterPtr _n_plus,_n_minus;
    Histo1DPtr _h_cTheta_A,_h_cTheta_B;
    ///@}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1814783);

}