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CLEOII_1997_I446031

$e^+e^-\to e^+e^-\pi^0, \eta, \eta^\prime$ via intermediate photons at 10.58 GeV
Experiment: CLEOII (CESR)
Inspire ID: 446031
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 57 (1998) 33-54
Beams: e+ e-
Beam energies: (5.3, 5.3) GeV
Run details:
  • e+ e- > e+e- meson via photon photon -> meson

Measurement of the cross sections for the production of $\pi^0, \eta, \eta^\prime$ in photon-photon collisions, i.e. $e^+e^-\to \gamma\gamma e^+e^-$ followed by $\gamma\gamma\to\pi^0, \eta, \eta^\prime$, by the CLEO II experiment at 10.58 GeV

Source code: CLEOII_1997_I446031.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5#include "Rivet/Projections/Beam.hh"
  6
  7namespace Rivet {
  8
  9
 10  /// @brief CLEO e+e- > e+e- pi0,eta,eta'
 11  class CLEOII_1997_I446031 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1997_I446031);
 16
 17
 18    /// @name Analysis methods
 19    ///@{
 20
 21    /// Book histograms and initialise projections before the run
 22    void init() {
 23
 24      // Initialise and register projections
 25      declare(Beam(), "Beams");
 26      declare(FinalState(),"FS");
 27      declare(UnstableParticles(), "UFS");
 28
 29      // book the histograms
 30      book(_h_pi0,1,1,1);
 31      for (unsigned int ix=0; ix<3; ++ix) book(_h_eta [ix],ix+2,1,1);
 32      for (unsigned int ix=0; ix<6; ++ix) book(_h_etap[ix],ix+5,1,1);
 33    }
 34
 35
 36    /// Perform the per-event analysis
 37    void analyze(const Event& event) {
 38      // find scattered leptons and calc Q2
 39      const Beam& beams = apply<Beam>(event, "Beams");
 40      double q12 = -1, q22 = -1;
 41      if (!findScattered(beams.beams().first,  q12)) vetoEvent;
 42      if (!findScattered(beams.beams().second, q22)) vetoEvent;
 43      double scale = max(q12,q22);
 44      // check the final state
 45      const FinalState & fs = apply<FinalState>(event, "FS");
 46      map<long,int> nCount;
 47      int ntotal(0);
 48      for (const Particle& p : fs.particles()) {
 49        nCount[p.pid()] += 1;
 50        ++ntotal;
 51      }
 52      // find the meson
 53      const FinalState& ufs = apply<FinalState>(event, "UFS");
 54      for (const Particle& p : ufs.particles(Cuts::pid==111 or
 55                                             Cuts::pid==221 or
 56                                             Cuts::pid==331)) {
 57        if(p.children().empty()) continue;
 58        map<long,int> nRes = nCount;
 59        int ncount = ntotal;
 60        findChildren(p,nRes,ncount);
 61        bool matched = true;
 62        for(auto const & val : nRes) {
 63          if(abs(val.first)==11) {
 64            if(val.second!=1) {
 65              matched = false;
 66              break;
 67            }
 68          }
 69          else if(val.second!=0) {
 70            matched = false;
 71            break;
 72          }
 73        }
 74        if (matched) {
 75          if (p.pid()==111) {
 76            _h_pi0->fill(scale);
 77          } else if (p.pid()==221) {
 78            for (unsigned int ix=0; ix<3; ++ix)
 79              _h_eta[ix]->fill(scale);
 80          } else if(p.pid()==331) {
 81            for (unsigned int ix=0; ix<6; ++ix)
 82              _h_etap[ix]->fill(scale);
 83          }
 84          break;
 85        }
 86      }
 87    }
 88
 89
 90    /// Normalise histograms etc., after the run
 91    void finalize() {
 92      // normalize the cross sections
 93      scale(_h_pi0, crossSection()/femtobarn/sumW());
 94      for(unsigned int ix=0;ix<3;++ix)
 95        scale(_h_eta[ix], crossSection()/femtobarn/sumW());
 96      for(unsigned int ix=0;ix<6;++ix)
 97        scale(_h_etap[ix], crossSection()/femtobarn/sumW());
 98    }
 99
100    ///@}
101
102
103    /// @name Helpers
104    /// @{
105
106    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
107      for (const Particle &child : p.children()) {
108        if (child.children().empty()) {
109          --nRes[child.pid()];
110          --ncount;
111        } else {
112          findChildren(child,nRes,ncount);
113        }
114      }
115    }
116
117
118    bool findScattered(Particle beam, double& q2) {
119      bool found = false;
120      Particle scat = beam;
121      while (!scat.children().empty()) {
122        found = false;
123        for (const Particle & p : scat.children()) {
124          if (p.pid()==scat.pid()) {
125            scat=p;
126            found=true;
127            break;
128          }
129        }
130        if (!found) break;
131      }
132      if (!found) return false;
133      q2 = -(beam.momentum() - scat.momentum()).mass2();
134      return true;
135    }
136
137    /// @}
138
139
140    /// @name Histograms
141    /// @{
142    Histo1DPtr _h_pi0,_h_eta[3],_h_etap[6];
143    /// @}
144
145  };
146
147
148  RIVET_DECLARE_PLUGIN(CLEOII_1997_I446031);
149
150}