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Rivet analyses reference

BESIII_2020_I1762922

Cross Section for $e^+e^-\to\eta^\prime J/\psi$ for energies between 4.178 and 4.6 GeV
Experiment: BESIII (BEPC)
Inspire ID: 1762922
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D101 (2020) no.1, 012008
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); (2.1, 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); (2.3, 2.3) GeV
Run details:
  • e+ e- to hadrons

Cross section for $e^+e^-\to\eta^\prime J/\psi$ for energies between 4.178 and 4.6 GeV measured by the BESIII collaboration. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples.

Source code: BESIII_2020_I1762922.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- > eta' J/psi
 10  class BESIII_2020_I1762922 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1762922);
 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, 1,1,1);
 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()) MSG_ERROR("Beam energy incompatible with analysis.");
 33    }
 34
 35    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 36      for (const Particle &child : p.children()) {
 37        if (child.children().empty()) {
 38          --nRes[child.pid()];
 39          --ncount;
 40        }
 41        else {
 42          findChildren(child,nRes,ncount);
 43        }
 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& p : ufs.particles(Cuts::pid==443)) {
 58        if(p.children().empty()) continue;
 59        map<long,int> nRes = nCount;
 60        int ncount = ntotal;
 61        findChildren(p,nRes,ncount);
 62        bool matched=false;
 63        for (const Particle& p2 : ufs.particles(Cuts::pid==331)) {
 64          if (p2.children().empty()) continue;
 65          bool psiParent=false;
 66          Particle parent=p2;
 67          while (!parent.parents().empty()) {
 68            parent=parent.parents()[0];
 69            if (parent.pid()==443) {
 70              psiParent=true;
 71              break;
 72            }
 73          }
 74          if (psiParent) continue;
 75          map<long,int> nRes2 = nRes;
 76          int ncount2 = ncount;
 77          findChildren(p2,nRes2,ncount2);
 78          if (ncount2!=0) continue;
 79          matched = true;
 80          for (const auto& val : nRes2) {
 81            if (val.second!=0) {
 82              matched = false;
 83              break;
 84            }
 85          }
 86          if(matched) {
 87            _nJPsi->fill(_ecms);
 88            break;
 89          }
 90        }
 91      }
 92    }
 93
 94
 95    /// Normalise histograms etc., after the run
 96    void finalize() {
 97      scale(_nJPsi, crossSection()/ sumOfWeights() /picobarn);
 98    }
 99
100    /// @}
101
102
103    /// @name Histograms
104    /// @{
105    BinnedHistoPtr<string> _nJPsi;
106    string _ecms;
107    /// @}
108
109  };
110
111
112
113  RIVET_DECLARE_PLUGIN(BESIII_2020_I1762922);
114
115}