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Rivet analyses reference

BESIII_2016_I1457597

Cross section for $e^+e^-\to J/\psi \eta^\prime$ at energies between 4.189 and 4.6 GeV
Experiment: BESIII (BEPC)
Inspire ID: 1457597
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D94 (2016) 032009, 2016
Beams: e+ e-
Beam energies: (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3) GeV
Run details:
  • e+e- to hadrons

Measurement of the cross section for $e^+e^-\to J/\psi \eta^\prime$ at energies between 4.189 and 4.6 GeV. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples.

Source code: BESIII_2016_I1457597.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 Cross section for $e^+e^-\to J/\psi \eta^\prime$ at energies between 4.189 and 4.6 GeV
 10  class BESIII_2016_I1457597 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1457597);
 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, 1, 1, 7);
 25      for (const string& en : _nJPsi.binning().edges<0>()) {
 26        const double end = std::stod(en)*GeV;
 27        if (isCompatibleWithSqrtS(end)) {
 28          _ecms = en;
 29          break;
 30        }
 31      }
 32      if (_ecms.empty())
 33        MSG_ERROR("Beam energy incompatible with analysis.");
 34    }
 35
 36    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 37      for(const Particle &child : p.children()) {
 38        if(child.children().empty()) {
 39          --nRes[child.pid()];
 40          --ncount;
 41        }
 42        else
 43          findChildren(child,nRes,ncount);
 44      }
 45    }
 46
 47    /// Perform the per-event analysis
 48    void analyze(const Event& event) {
 49      const FinalState& fs = apply<FinalState>(event, "FS");
 50      map<long,int> nCount;
 51      int ntotal(0);
 52      for (const Particle& p : fs.particles()) {
 53        nCount[p.pid()] += 1;
 54        ++ntotal;
 55      }
 56      const FinalState& ufs = apply<FinalState>(event, "UFS");
 57      for (const Particle& p1 : ufs.particles()) {
 58        bool matched=false;
 59        if(p1.children().empty()) continue;
 60        // find the j/psi
 61        if(p1.pid()!=443) continue;
 62        map<long,int> nRes = nCount;
 63        int ncount = ntotal;
 64        findChildren(p1,nRes,ncount);
 65
 66        for (const Particle& p2 : ufs.particles()) {
 67          if(p2.children().empty()) continue;
 68          // find the j/psi
 69          if(p2.pid()!=331) continue;
 70          map<long,int> nRes2 = nRes;
 71          int ncount2 = ncount;
 72          findChildren(p2,nRes2,ncount2);
 73          if(ncount2!=0) continue;
 74          matched=true;
 75          for(auto const & val : nRes2) {
 76            if(val.second!=0) {
 77              matched = false;
 78              break;
 79            }
 80          }
 81          if(matched) {
 82            _nJPsi->fill(_ecms);
 83            break;
 84          }
 85        }
 86        if(matched) break;
 87      }
 88    }
 89
 90    /// Normalise histograms etc., after the run
 91    void finalize() {
 92      scale(_nJPsi, crossSection()/ sumOfWeights() /picobarn);
 93    }
 94
 95    /// @}
 96
 97
 98    /// @name Histograms
 99    /// @{
100    BinnedHistoPtr<string> _nJPsi;
101    string _ecms;
102    /// @}
103
104
105  };
106
107
108  RIVET_DECLARE_PLUGIN(BESIII_2016_I1457597);
109
110
111}