rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

BESIII_2015_I1377204

Cross section for $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeV
Experiment: BESIII (BEPC)
Inspire ID: 1377204
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.Lett. 115 (2015) 112003, 2015
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Measurement of the cross section for $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeV

Source code: BESIII_2015_I1377204.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 $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeV
 10  class BESIII_2015_I1377204 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1377204);
 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, "TMP/jpsi");
 25    }
 26
 27
 28    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 29      for (const Particle &child : p.children()) {
 30        if(child.children().empty()) {
 31          --nRes[child.pid()];
 32          --ncount;
 33        }
 34        else
 35          findChildren(child,nRes,ncount);
 36      }
 37    }
 38
 39    /// Perform the per-event analysis
 40    void analyze(const Event& event) {
 41      const FinalState& fs = apply<FinalState>(event, "FS");
 42      map<long,int> nCount;
 43      int ntotal(0);
 44      for (const Particle& p : fs.particles()) {
 45        nCount[p.pid()] += 1;
 46        ++ntotal;
 47      }
 48      const FinalState& ufs = apply<FinalState>(event, "UFS");
 49      for (const Particle& p : ufs.particles()) {
 50        if(p.children().empty()) continue;
 51        // find the j/psi
 52        if(p.pid()==443) {
 53          map<long,int> nRes = nCount;
 54          int ncount = ntotal;
 55          findChildren(p,nRes,ncount);
 56          // J/psi pi0pi0
 57          if(ncount!=2) continue;
 58          bool matched = true;
 59          for(auto const & val : nRes) {
 60            if(abs(val.first)==111) {
 61              if(val.second !=2) {
 62                matched = false;
 63                break;
 64              }
 65            }
 66            else if(val.second!=0) {
 67              matched = false;
 68              break;
 69            }
 70          }
 71          if(matched) {
 72            _nJPsi->fill();
 73            break;
 74          }
 75        }
 76      }
 77    }
 78
 79
 80    /// Normalise histograms etc., after the run
 81    void finalize() {
 82      double sigma = _nJPsi->val();
 83      double error = _nJPsi->err();
 84      sigma *= crossSection()/ sumOfWeights() /picobarn;
 85      error *= crossSection()/ sumOfWeights() /picobarn;
 86      Estimate1DPtr  mult;
 87      book(mult, 1, 1, 12);
 88      for (auto& b : mult->bins()) {
 89        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
 90          b.set(sigma, error);
 91        }
 92      }
 93    }
 94
 95    /// @}
 96
 97
 98    /// @name Histograms
 99    /// @{
100    CounterPtr _nJPsi;
101    /// @}
102
103
104  };
105
106
107  RIVET_DECLARE_PLUGIN(BESIII_2015_I1377204);
108
109
110}