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D0_2009_S8349509

Z+jets angular distributions
Experiment: D0 (Tevatron Run 2)
Inspire ID: 826756
Status: VALIDATED
Authors:
  • Frank Siegert
References: Beams: p- p+
Beam energies: (980.0, 980.0) GeV
Run details:
  • $p \bar{p} \to \mu^+ \mu^-$ + jets at 1960 GeV. Needs mass cut on lepton pair to avoid photon singularity, looser than $65 < m_{ee} < 115$ GeV.

First measurements at a hadron collider of differential cross sections for $Z (\to \mu\mu)$+jet+X production in $\Delta\phi(Z, j)$, $|\Delta y(Z, j)|$ and $|y_\mathrm{boost}(Z, j)|$. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.

Source code: D0_2009_S8349509.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/ZFinder.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {


  /// @brief D0 Z+jets angular distributions
  class D0_2009_S8349509 : public Analysis {
  public:

    /// @name Constructors etc.
    //@{

    /// Constructor
    D0_2009_S8349509()
      : Analysis("D0_2009_S8349509"),
        _inclusive_Z_sumofweights(0)
    {    }

    //@}


    /// @name Analysis methods
    //@{

    /// Book histograms
    void init() {
      Cut cut = Cuts::abseta < 1.7 && Cuts::pT > 15*GeV;
      ZFinder zfinder(FinalState(), cut, PID::MUON, 65*GeV, 115*GeV, 0.2, ZFinder::NOCLUSTER, ZFinder::TRACK);
      declare(zfinder, "ZFinder");

      FastJets conefinder(zfinder.remainingFinalState(), FastJets::D0ILCONE, 0.5);
      declare(conefinder, "ConeFinder");

      _h_dphi_jet_Z25 = bookHisto1D(1, 1, 1);
      _h_dphi_jet_Z45 = bookHisto1D(2, 1, 1);

      _h_dy_jet_Z25 = bookHisto1D(3, 1, 1);
      _h_dy_jet_Z45 = bookHisto1D(4, 1, 1);

      _h_yboost_jet_Z25 = bookHisto1D(5, 1, 1);
      _h_yboost_jet_Z45 = bookHisto1D(6, 1, 1);

      _h_dphi_jet_Z25_xs = bookHisto1D(1, 1, 2);
      _h_dphi_jet_Z45_xs = bookHisto1D(2, 1, 2);

      _h_dy_jet_Z25_xs = bookHisto1D(3, 1, 2);
      _h_dy_jet_Z45_xs = bookHisto1D(4, 1, 2);

      _h_yboost_jet_Z25_xs = bookHisto1D(5, 1, 2);
      _h_yboost_jet_Z45_xs = bookHisto1D(6, 1, 2);

      _inclusive_Z_sumofweights = 0;
    }


    void analyze(const Event& event) {
      const double weight = event.weight();

      const ZFinder& zfinder = apply<ZFinder>(event, "ZFinder");
      if (zfinder.bosons().size() == 1) {
        // count inclusive sum of weights for histogram normalisation
        _inclusive_Z_sumofweights += weight;

        const FourMomentum& zmom = zfinder.bosons()[0].momentum();
        if (zmom.pT() < 25*GeV) vetoEvent;

        Jets jets;
        foreach (const Jet& j, apply<JetAlg>(event, "ConeFinder").jetsByPt(20*GeV)) {
          if (j.abseta() < 2.8) {
            jets.push_back(j);
            break;
          }
        }

        // Return if there are no jets:
        if (jets.size() < 1) {
          MSG_DEBUG("Skipping event " << numEvents() << " because no jets pass cuts ");
          vetoEvent;
        }

        const FourMomentum& jetmom = jets[0].momentum();
        const double yZ = zmom.rapidity();
        const double yjet = jetmom.rapidity();
        const double dphi = deltaPhi(zmom, jetmom);
        const double dy = deltaRap(zmom, jetmom);
        const double yboost = fabs(yZ+yjet)/2;

        if (zmom.pT() > 25*GeV) {
          _h_dphi_jet_Z25->fill(dphi, weight);
          _h_dy_jet_Z25->fill(dy, weight);
          _h_yboost_jet_Z25->fill(yboost, weight);
          _h_dphi_jet_Z25_xs->fill(dphi, weight);
          _h_dy_jet_Z25_xs->fill(dy, weight);
          _h_yboost_jet_Z25_xs->fill(yboost, weight);
        }
        if (zmom.pT() > 45*GeV) {
          _h_dphi_jet_Z45->fill(dphi, weight);
          _h_dy_jet_Z45->fill(dy, weight);
          _h_yboost_jet_Z45->fill(yboost, weight);
          _h_dphi_jet_Z45_xs->fill(dphi, weight);
          _h_dy_jet_Z45_xs->fill(dy, weight);
          _h_yboost_jet_Z45_xs->fill(yboost, weight);
        }
      }

    }


    void finalize() {
      if (_inclusive_Z_sumofweights == 0) return;
      scale(_h_dphi_jet_Z25, 1/_inclusive_Z_sumofweights);
      scale(_h_dphi_jet_Z45, 1/_inclusive_Z_sumofweights);
      scale(_h_dy_jet_Z25, 1/_inclusive_Z_sumofweights);
      scale(_h_dy_jet_Z45, 1/_inclusive_Z_sumofweights);
      scale(_h_yboost_jet_Z25, 1/_inclusive_Z_sumofweights);
      scale(_h_yboost_jet_Z45, 1/_inclusive_Z_sumofweights);

      scale(_h_dphi_jet_Z25_xs, crossSectionPerEvent());
      scale(_h_dphi_jet_Z45_xs, crossSectionPerEvent());
      scale(_h_dy_jet_Z25_xs, crossSectionPerEvent());
      scale(_h_dy_jet_Z45_xs, crossSectionPerEvent());
      scale(_h_yboost_jet_Z25_xs, crossSectionPerEvent());
      scale(_h_yboost_jet_Z45_xs, crossSectionPerEvent());
    }

    //@}

  private:

    // Data members like post-cuts event weight counters go here

  private:

    /// @name Histograms (normalised)
    //@{
    Histo1DPtr _h_dphi_jet_Z25;
    Histo1DPtr _h_dphi_jet_Z45;

    Histo1DPtr _h_dy_jet_Z25;
    Histo1DPtr _h_dy_jet_Z45;

    Histo1DPtr _h_yboost_jet_Z25;
    Histo1DPtr _h_yboost_jet_Z45;
    //@}

    /// @name Histograms (absolute cross sections)
    //@{
    Histo1DPtr _h_dphi_jet_Z25_xs;
    Histo1DPtr _h_dphi_jet_Z45_xs;

    Histo1DPtr _h_dy_jet_Z25_xs;
    Histo1DPtr _h_dy_jet_Z45_xs;

    Histo1DPtr _h_yboost_jet_Z25_xs;
    Histo1DPtr _h_yboost_jet_Z45_xs;
    //@}

    double _inclusive_Z_sumofweights;

  };



  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(D0_2009_S8349509);

}