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TPC_1985_I205868

Photon and $\pi^0$ spectra at 29 GeV
Experiment: TPC (PEP)
Inspire ID: 205868
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Z.Phys. C27 (1985) 187, 1985
Beams: e+ e-
Beam energies: (14.5, 14.5) GeV
Run details:
  • e+e- to hadronas at 29 GeV

Measurement of the photon and $\pi^0$ spectra at 29 GeV by the TPC experiment.

Source code: TPC_1985_I205868.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/Beam.hh"
 4#include "Rivet/Projections/FinalState.hh"
 5#include "Rivet/Projections/ChargedFinalState.hh"
 6#include "Rivet/Projections/UnstableParticles.hh"
 7
 8namespace Rivet {
 9
10
11  /// @brief pi0 and gamma spectra at 29 GeV
12  class TPC_1985_I205868 : public Analysis {
13  public:
14
15    /// Constructor
16    RIVET_DEFAULT_ANALYSIS_CTOR(TPC_1985_I205868);
17
18
19    /// @name Analysis methods
20    //@{
21
22    /// Book histograms and initialise projections before the run
23    void init() {
24      declare(Beam(), "Beams");
25      declare(ChargedFinalState(), "FS");
26      declare(UnstableParticles(), "UFS");
27      book(_histPhoton, 1, 1, 1);
28      book(_histPi    , 2, 1, 1);
29    }
30
31
32    /// Perform the per-event analysis
33    void analyze(const Event& event) {
34
35      // First, veto on leptonic events by requiring at least 4 charged FS particles
36      const FinalState& fs = apply<FinalState>(event, "FS");
37      const size_t numParticles = fs.particles().size();
38
39      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
40      if (numParticles < 2) {
41        MSG_DEBUG("Failed leptonic event cut");
42        vetoEvent;
43      }
44      MSG_DEBUG("Passed leptonic event cut");
45
46      // Get beams and average beam momentum
47      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
48      const double meanBeamMom = ( beams.first.p3().mod() +
49                                   beams.second.p3().mod() ) / 2.0;
50      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
51
52      // Final state of unstable particles to get particle spectra
53      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
54
55      for( const Particle& p : ufs.particles()) {
56        const int id = p.abspid();
57        double xE = p.E()/meanBeamMom;
58        switch (id) {
59        case 22: // Photons
60          _histPhoton->fill(xE);
61          break;
62        case 111: // Neutral pions
63          _histPi->fill(xE);
64          break;
65	}
66      }
67
68    }
69
70
71    /// Normalise histograms etc., after the run
72    void finalize() {
73      scale(_histPhoton, 1./sumOfWeights());
74      scale(_histPi    , 1./sumOfWeights());
75    }
76
77    //@}
78
79
80    /// @name Histograms
81    //@{
82    Histo1DPtr _histPhoton;
83    Histo1DPtr _histPi    ;
84    //@}
85
86
87  };
88
89
90  // The hook for the plugin system
91  RIVET_DECLARE_PLUGIN(TPC_1985_I205868);
92
93
94}