rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

BESIII_2020_I1784442

Cross Section for $e^+e^-\to\eta J/\psi$ for energies between 3.81 and 4.60 GeV
Experiment: BESIII (BEPC)
Inspire ID: 1784442
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 102 (2020) 3, 031101
Beams: e+ e-
Beam energies: (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (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); (2.1, 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); (2.1, 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); (2.1, 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); (2.1, 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); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (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); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3) GeV
Run details:
  • e+ e- to hadrons

Cross section for $e^+e^-\to\eta J/\psi$ for energies between 3.81 and 4.60 GeV measured by the BESIII collaboration.

Source code: BESIII_2020_I1784442.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_I1784442 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1784442);
 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      for (unsigned int ix=0; ix<2; ++ix) {
 25        book(_sigmaJPsi[ix], 1+ix, 1, 1);
 26        for(const string& en : _sigmaJPsi[ix].binning().edges<0>()) {
 27          const double end = std::stod(en)*GeV;
 28          if (isCompatibleWithSqrtS(end)) {
 29            _ecms[ix] = en;
 30            break;
 31          }
 32        }
 33      }
 34      if (_ecms[0].empty() && _ecms[1].empty()) {
 35        MSG_ERROR("Beam energy incompatible with analysis.");
 36      }
 37    }
 38
 39    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 40      for (const Particle &child : p.children()) {
 41        if (child.children().empty()) {
 42          --nRes[child.pid()];
 43          --ncount;
 44        }
 45        else {
 46          findChildren(child,nRes,ncount);
 47        }
 48      }
 49    }
 50
 51    /// Perform the per-event analysis
 52    void analyze(const Event& event) {
 53      const FinalState& fs = apply<FinalState>(event, "FS");
 54      map<long,int> nCount;
 55      int ntotal(0);
 56      for (const Particle& p : fs.particles()) {
 57        nCount[p.pid()] += 1;
 58        ++ntotal;
 59      }
 60      const FinalState& ufs = apply<FinalState>(event, "UFS");
 61      for (const Particle& p : ufs.particles(Cuts::pid==PID::JPSI)) {
 62        if (p.children().empty()) continue;
 63        // find the J/psi
 64        map<long,int> nRes = nCount;
 65        int ncount = ntotal;
 66        findChildren(p,nRes,ncount);
 67        bool matched=false;
 68        for (const Particle& p2 : ufs.particles(Cuts::pid==PID::ETA)) {
 69          if(p2.children().empty()) continue;
 70          bool JpsiParent=false;
 71          Particle parent=p2;
 72          while (!parent.parents().empty()) {
 73            parent=parent.parents()[0];
 74            if (parent.pid()==PID::JPSI) {
 75              JpsiParent=true;
 76              break;
 77            }
 78          }
 79          if (JpsiParent) continue;
 80          map<long,int> nRes2 = nRes;
 81          int ncount2 = ncount;
 82          findChildren(p2,nRes2,ncount2);
 83          if (ncount2!=0) continue;
 84          matched = true;
 85          for (const auto& val : nRes2) {
 86            if (val.second!=0) {
 87              matched = false;
 88              break;
 89            }
 90          }
 91          if (matched) {
 92            for (unsigned int ix=0; ix<2; ++ix)
 93              if (!_ecms[ix].empty()) {
 94                _sigmaJPsi[ix]->fill(_ecms[ix]);
 95                break;
 96              }
 97            }
 98          }
 99          if (matched) break;
100        }
101      }
102
103
104    /// Normalise histograms etc., after the run
105    void finalize() {
106      scale(_sigmaJPsi, crossSection()/ sumOfWeights() /picobarn);
107    }
108
109    /// @}
110
111
112    /// @name Histograms
113    /// @{
114    BinnedHistoPtr<string> _sigmaJPsi[2];
115    string _ecms[2];
116    /// @}
117
118
119  };
120
121
122  RIVET_DECLARE_PLUGIN(BESIII_2020_I1784442);
123
124}