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BELLE_2013_I1225975

Cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.8 and 4.82 GeV
Experiment: BELLE (KEKB)
Inspire ID: 1225975
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.Lett. 110 (2013) 252002, 2013
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Measurement of the cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.8 and 4.82 GeV using radiative return by BELLE.

Source code: BELLE_2013_I1225975.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- J/Psi
 10  class BELLE_2013_I1225975 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2013_I1225975);
 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    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 28      for (const Particle &child : p.children()) {
 29	if(child.children().empty()) {
 30	  --nRes[child.pid()];
 31	  --ncount;
 32	}
 33	else
 34	  findChildren(child,nRes,ncount);
 35      }
 36    }
 37
 38    /// Perform the per-event analysis
 39    void analyze(const Event& event) {
 40      const FinalState& fs = apply<FinalState>(event, "FS");
 41      map<long,int> nCount;
 42      int ntotal(0);
 43      for (const Particle& p : fs.particles()) {
 44	nCount[p.pid()] += 1;
 45	++ntotal;
 46      }
 47      const FinalState& ufs = apply<FinalState>(event, "UFS");
 48      for (const Particle& p : ufs.particles()) {
 49	if(p.children().empty()) continue;
 50	// find the omega
 51	if(p.pid()==443) {
 52	  map<long,int> nRes = nCount;
 53	  int ncount = ntotal;
 54	  findChildren(p,nRes,ncount);
 55	  // omega pi+pi-
 56	  if(ncount!=2) continue;
 57	  bool matched = true;
 58	  for(auto const & val : nRes) {
 59	    if(abs(val.first)==211) {
 60	      if(val.second !=1) {
 61		matched = false;
 62		break;
 63	      }
 64	    }
 65	    else if(val.second!=0) {
 66	      matched = false;
 67	      break;
 68	    }
 69	  }
 70	  if(matched) {
 71	    _nJPsi->fill();
 72	    break;
 73	  }
 74	}
 75      }
 76    }
 77
 78
 79    /// Normalise histograms etc., after the run
 80    void finalize() {
 81      double sigma =  _nJPsi->val();
 82      double error = _nJPsi->err();
 83      sigma *= crossSection()/ sumOfWeights() /picobarn;
 84      error *= crossSection()/ sumOfWeights() /picobarn;
 85      Estimate1DPtr  mult;
 86      book(mult, 1, 1, 1);
 87      for (auto& b : mult->bins()) {
 88        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
 89          b.set(sigma, error);
 90        }
 91      }
 92    }
 93
 94    /// @}
 95
 96
 97    /// @name Histograms
 98    /// @{
 99    CounterPtr _nJPsi;
100    /// @}
101
102
103  };
104
105  RIVET_DECLARE_PLUGIN(BELLE_2013_I1225975);
106
107}