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CELLO_1989_I276764

Photon, $\pi^0$ and $\eta$ spectra at 35 GeV
Experiment: CELLO ()
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Z.Phys. C47 (1990) 1-10, 1990
Beams: e+ e-
Beam energies: (17.5, 17.5) GeV
Run details:
  • e+ e- to hadrons

Measurement of the $\gamma$, $\pi^0$ and $\eta$ energy fractions in $e^+e^-$ collisions for centre-of-mass energy of 35 GeV by the CELLO experiment at Petra. Only the bin centroids are given in the paper and HEPdata so the bin widths have been infered.

Source code: CELLO_1989_I276764.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/Beam.hh"

namespace Rivet {


  /// @brief Add a short analysis description here
  class CELLO_1989_I276764 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(CELLO_1989_I276764);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // Book histograms
      book(_h_gamma , 2, 1, 1);
      book(_h_pi0A  , 3, 1, 1);
      book(_h_pi0B  , 4, 1, 1);
      book(_h_eta   , 5, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // at least 5 charged FS particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      const size_t numParticles = fs.particles().size();

      if (numParticles < 5) {
        MSG_DEBUG("Failed leptonic event cut");
        vetoEvent;
      }
      MSG_DEBUG("Passed leptonic event cut");

      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      const double meanBeamMom = ( beams.first.p3().mod() +
                                   beams.second.p3().mod() ) / 2.0;
      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);

      // Final state to get particle spectra
      for (const Particle& p : apply<UnstableFinalState>(event, "UFS").particles(Cuts::pid==111 || Cuts::pid==221)) {
	double xE = p.E()/meanBeamMom;
	if(p.pid()==111) {
	  _h_pi0A->fill(xE);
	  _h_pi0B->fill(xE);
	}
	else
	  _h_eta->fill(xE);
      }
      for (const Particle& p : apply<FinalState>(event, "FS").particles(Cuts::pid==111 || Cuts::pid==22)) {
	double xE = p.E()/meanBeamMom;
	if(p.pid()==22)
	  _h_gamma->fill(xE);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {

      double fact = sqr(sqrtS())/GeV2*crossSection()/microbarn/sumOfWeights();
      scale(_h_gamma, fact); 
      scale(_h_pi0A , fact); 
      scale(_h_pi0B , fact); 
      scale(_h_eta  , fact); 

    }

    //@}


    /// @name Histograms
    //@{
    Histo1DPtr _h_gamma,_h_pi0A,_h_pi0B,_h_eta;


  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(CELLO_1989_I276764);


}