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Rivet analyses reference

BESIII_2020_I1836509

Cross section for $e^+e^-\to\eta^\prime\pi^+\pi^-$ for energies between 2.00 and 3.08 GeV
Experiment: BESIII (BEPC)
Inspire ID: 1836509
Status: VALIDATED
Authors:
  • Peter Richardson
References: Beams: e+ e-
Beam energies: (1.0, 1.0); (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.3, 1.3); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5) GeV
Run details:
  • e+ e- to hadrons

Measurement of the cross section for $e^+e^-\to\eta^\prime\pi^+\pi^-$ for energies between 2.00 and 3.08 GeV by the BESIII collaboration. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples.

Source code: BESIII_2020_I1836509.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 e+e- > pi+pi- eta'
 10  class BESIII_2020_I1836509 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1836509);
 15
 16
 17    /// @name Analysis methods
 18    ///@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      // Initialise and register projections
 23      declare(FinalState(), "FS");
 24      declare(UnstableParticles(), "UFS");
 25      // histograms
 26      book(_nPiPiEta, 1, 1, 1);
 27      for (const string& en : _nPiPiEta.binning().edges<0>()) {
 28        const double end = std::stod(en)*GeV;
 29        if (isCompatibleWithSqrtS(end)) {
 30          _ecms = en;
 31          break;
 32        }
 33      }
 34      if(_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
 35    }
 36
 37    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 38      for(const Particle &child : p.children()) {
 39	if(child.children().empty()) {
 40	  nRes[child.pid()]-=1;
 41	  --ncount;
 42	}
 43	else
 44	  findChildren(child,nRes,ncount);
 45      }
 46    }
 47
 48    /// Perform the per-event analysis
 49    void analyze(const Event& event) {
 50      const FinalState& fs = apply<FinalState>(event, "FS");
 51
 52      map<long,int> nCount;
 53      int ntotal(0);
 54      for (const Particle& p : fs.particles()) {
 55	nCount[p.pid()] += 1;
 56	++ntotal;
 57      }
 58      const FinalState& ufs = apply<FinalState>(event, "UFS");
 59      for (const Particle& p : ufs.particles(Cuts::pid==331)) {
 60	if(p.children().empty()) continue;
 61	map<long,int> nRes = nCount;
 62	int ncount = ntotal;
 63	findChildren(p,nRes,ncount);
 64	if(ncount!=2) continue;
 65	bool matched = true;
 66	for(auto const & val : nRes) {
 67	  if(abs(val.first)==211) {
 68	    if(val.second!=1) {
 69	      matched = false;
 70	      break;
 71	    }
 72	  }
 73	  else if(val.second!=0) {
 74	    matched = false;
 75	    break;
 76	  }
 77	}
 78	if(matched) _nPiPiEta->fill(_ecms);
 79      }
 80    }
 81
 82
 83    /// Normalise histograms etc., after the run
 84    void finalize() {
 85      scale(_nPiPiEta, crossSection()/ sumOfWeights() /picobarn);
 86    }
 87    ///@}
 88
 89
 90    /// @name Histograms
 91    ///@{
 92    BinnedHistoPtr<string> _nPiPiEta;
 93    string _ecms;
 94    ///@}
 95
 96
 97  };
 98
 99
100  RIVET_DECLARE_PLUGIN(BESIII_2020_I1836509);
101
102}