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ATLAS_2011_S9131140

Measurement of the Z pT with electrons and muons at 7 TeV
Experiment: ATLAS (LHC)
Inspire ID: 917931
Status: VALIDATED
Authors:
  • Elena Yatsenko
  • Judith Katzy
References: Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Run with inclusive $Z$ events, with $Z/\gamma^*$ decays to electrons and/or muons.

The Z pT at $\sqrt{s} = 7$\;TeV is measured using electron and muon $Z$ decay channels. The dressed leptons definition uses photons clustered in a cone around the charged leptons, while the bare lepton definition uses the post-FSR charged leptons only in the $Z$ reconstruction. The data used in the bare leptons calculation are based on a forward application of a PHOTOS-based energy loss correction and are hence not quite model-independent.

Source code: ATLAS_2011_S9131140.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ZFinder.hh"

namespace Rivet {


  /// @brief ATLAS Z pT in Drell-Yan events at 7 TeV
  /// @author Elena Yatsenko, Judith Katzy
  class ATLAS_2011_S9131140 : public Analysis {
  public:

    /// Constructor
    ATLAS_2011_S9131140()
      : Analysis("ATLAS_2011_S9131140")
    {
      _sumw_el_bare = 0;
      _sumw_el_dressed = 0;
      _sumw_mu_bare = 0;
      _sumw_mu_dressed = 0;
    }


    /// @name Analysis methods
    //@{

    void init() {

      // Set up projections
      FinalState fs;
      Cut cut = Cuts::abseta < 2.4 && Cuts::pT > 20*GeV;

      ZFinder zfinder_dressed_el(fs, cut, PID::ELECTRON, 66.0*GeV, 116.0*GeV, 0.1, ZFinder::CLUSTERNODECAY);
      declare(zfinder_dressed_el, "ZFinder_dressed_el");
      ZFinder zfinder_bare_el(fs, cut, PID::ELECTRON, 66.0*GeV, 116.0*GeV, 0.0, ZFinder::NOCLUSTER);
      declare(zfinder_bare_el, "ZFinder_bare_el");
      ZFinder zfinder_dressed_mu(fs, cut, PID::MUON, 66.0*GeV, 116.0*GeV, 0.1, ZFinder::CLUSTERNODECAY);
      declare(zfinder_dressed_mu, "ZFinder_dressed_mu");
      ZFinder zfinder_bare_mu(fs, cut, PID::MUON, 66.0*GeV, 116.0*GeV, 0.0, ZFinder::NOCLUSTER);
      declare(zfinder_bare_mu, "ZFinder_bare_mu");

      // Book histograms
      _hist_zpt_el_dressed     = bookHisto1D(1, 1, 2);  // electron "dressed"
      _hist_zpt_el_bare        = bookHisto1D(1, 1, 3);  // electron "bare"
      _hist_zpt_mu_dressed     = bookHisto1D(2, 1, 2);  // muon "dressed"
      _hist_zpt_mu_bare        = bookHisto1D(2, 1, 3);  // muon "bare"
    }


    /// Do the analysis
    void analyze(const Event& evt) {
      const double weight = evt.weight();

      const ZFinder& zfinder_dressed_el = apply<ZFinder>(evt, "ZFinder_dressed_el");
      if (!zfinder_dressed_el.bosons().empty()) {
        _sumw_el_dressed += weight;
        const FourMomentum pZ = zfinder_dressed_el.bosons()[0].momentum();
        _hist_zpt_el_dressed->fill(pZ.pT()/GeV, weight);
      }

      const ZFinder& zfinder_bare_el = apply<ZFinder>(evt, "ZFinder_bare_el");
      if (!zfinder_bare_el.bosons().empty()) {
        _sumw_el_bare += weight;
	    const FourMomentum pZ = zfinder_bare_el.bosons()[0].momentum();
        _hist_zpt_el_bare->fill(pZ.pT()/GeV, weight);
      }

      const ZFinder& zfinder_dressed_mu = apply<ZFinder>(evt, "ZFinder_dressed_mu");
      if (!zfinder_dressed_mu.bosons().empty()) {
        _sumw_mu_dressed += weight;
        const FourMomentum pZ = zfinder_dressed_mu.bosons()[0].momentum();
        _hist_zpt_mu_dressed->fill(pZ.pT()/GeV, weight);
      }

      const ZFinder& zfinder_bare_mu = apply<ZFinder>(evt, "ZFinder_bare_mu");
      if (!zfinder_bare_mu.bosons().empty()) {
        _sumw_mu_bare += weight;
        const FourMomentum pZ = zfinder_bare_mu.bosons()[0].momentum();
        _hist_zpt_mu_bare->fill(pZ.pT()/GeV, weight);
      }

    }


    void finalize() {
      if (_sumw_el_dressed != 0) scale(_hist_zpt_el_dressed, 1/_sumw_el_dressed);
      if (_sumw_el_bare    != 0) scale(_hist_zpt_el_bare,    1/_sumw_el_bare);
      if (_sumw_mu_dressed != 0) scale(_hist_zpt_mu_dressed, 1/_sumw_mu_dressed);
      if (_sumw_mu_bare    != 0) scale(_hist_zpt_mu_bare,    1/_sumw_mu_bare);
    }

    //@}


    private:

	double _sumw_el_bare, _sumw_el_dressed;
	double _sumw_mu_bare, _sumw_mu_dressed;

	Histo1DPtr _hist_zpt_el_dressed;
	Histo1DPtr _hist_zpt_el_bare;
	Histo1DPtr _hist_zpt_mu_dressed;
	Histo1DPtr _hist_zpt_mu_bare;
  };


  // Hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2011_S9131140);

}