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ALEPH_1991_S2435284

Hadronic Z decay charged multiplicity measurement
Experiment: ALEPH (LEP 1)
Inspire ID: 319520
Status: VALIDATED
Authors:
  • Andy Buckley
References:
  • Phys. Lett. B, 273, 181 (1991)
Beams: e+ e-
Beam energies: (45.6, 45.6) GeV
Run details:
  • Hadronic Z decay events generated on the Z pole ($\sqrt{s} = 91.2$ GeV)

The charged particle multiplicity distribution of hadronic Z decays, as measured on the peak of the Z resonance using the ALEPH detector at LEP. The unfolding procedure was model independent, and the distribution was found to have a mean of $20.85 \pm 0.24$, Comparison with lower energy data supports the KNO scaling hypothesis. The shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production.

Source code: ALEPH_1991_S2435284.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {


  /// @brief ALEPH LEP1 charged multiplicity in hadronic Z decay
  /// @author Andy Buckley
  class ALEPH_1991_S2435284 : public Analysis {
  public:

    /// Constructor.
    ALEPH_1991_S2435284()
      : Analysis("ALEPH_1991_S2435284")
    {
    }


    /// @name Analysis methods
    //@{

    /// Book projections and histogram
    void init() {
      const ChargedFinalState cfs;
      declare(cfs, "CFS");

      _histChTot = bookHisto1D(1, 1, 1);
      _histAver  = bookHisto1D(2, 1, 1);
    }


    /// Do the analysis
    void analyze(const Event& event) {
      const FinalState& cfs = apply<FinalState>(event, "CFS");
      MSG_DEBUG("Total charged multiplicity = " << cfs.size());
      _histChTot->fill(cfs.size(), event.weight());
      _histAver->fill(_histAver->bin(0).xMid(),cfs.size()*event.weight());
    }


    /// Normalize the histogram
    void finalize() {
      scale(_histChTot, 2.0/sumOfWeights()); // same as in ALEPH 1996
      scale(_histAver , 1./sumOfWeights());
    }

    //@}


  private:

    /// @name Histograms
    //@{
    Histo1DPtr _histChTot;
    Histo1DPtr _histAver;
    //@}

  };



  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ALEPH_1991_S2435284);

}