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ATLAS_2016_I1469071

Measurement of the WZ production cross section at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1469071
Status: VALIDATED
Authors:
  • Elena Yatsenko
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • pp -> WZ + X, diboson decays to electrons and muons

The production of $W^\pm Z$ events in proton--proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb${}^{-1}$ . The $W^\pm Z$ candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is $\sigma(W^\pm Z\to\ell^\prime\nu\ell\ell \text{fid.}) = 63.2\pm 3.2$(stat.)$\pm 2.6$(sys.)$\pm 1.5$(lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is 53.4-2.8+3.6 fb. The extrapolation of the measurement from the fiducial to the total phase space yields $\sigma(W^\pm Z\text{tot.})=50.6\pm 2.6$(stat.)$\pm 2.0$(sys.)$\pm 0.9$(th.)$\pm 1.2$(lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of 48.2-1.0+1.1 pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent $W^+Z$ and $W^-Z$ cross sections and their ratio. Users should note that explicit matching of lepton flavour between individual SM neutrinos and charged leptons is used in this analysis routine, to match the MC-based correction to the fiducial region applied in the paper. The data are therefore only valid under the assumption of the Standard Model and cannot be used for BSM reinterpretation.

Source code: ATLAS_2016_I1469071.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {


  /// @brief Measurement of the WZ production cross section at 13 TeV
  class ATLAS_2016_I1469071 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2016_I1469071);

    /// @name Analysis methods
    //@{

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

      // Lepton cuts
      Cut FS_Zlept = Cuts::abseta < 2.5 && Cuts::pT > 15*GeV;

      FinalState fs;
      Cut fs_z = Cuts::abseta < 2.5 && Cuts::pT > 15*GeV;
      Cut fs_j = Cuts::abseta < 4.5 && Cuts::pT > 25*GeV;

      // Get photons to dress leptons
      PromptFinalState photons(Cuts::abspid == PID::PHOTON);

      // Electrons and muons in Fiducial PS
      PromptFinalState leptons(FinalState(fs_z && (Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON)));
      leptons.acceptTauDecays(false);
      DressedLeptons dressedleptons(photons, leptons, 0.1, FS_Zlept, true);
      addProjection(dressedleptons, "DressedLeptons");

      // Electrons and muons in Total PS
      PromptFinalState leptons_total(Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON);
      leptons_total.acceptTauDecays(false);
      DressedLeptons dressedleptonsTotal(photons, leptons_total, 0.1, Cuts::open(), true);
      addProjection(dressedleptonsTotal, "DressedLeptonsTotal");

      // Promot neutrinos (yikes!)
      IdentifiedFinalState nu_id;
      nu_id.acceptNeutrinos();
      PromptFinalState neutrinos(nu_id);
      neutrinos.acceptTauDecays(false);
      declare(neutrinos, "Neutrinos");
      MSG_WARNING("\033[91;1mLIMITED VALIDITY - check info file for details!\033[m");

      // Jets
      VetoedFinalState veto;
      veto.addVetoOnThisFinalState(dressedleptons);
      FastJets jets(veto, FastJets::ANTIKT, 0.4);
      declare(jets, "Jets");

      // Book histograms
      _h_eee          = bookHisto1D(1, 1, 1);
      _h_mee          = bookHisto1D(1, 1, 2);
      _h_emm          = bookHisto1D(1, 1, 3);
      _h_mmm          = bookHisto1D(1, 1, 4);
      _h_fid          = bookHisto1D(1, 1, 5);
      _h_eee_Plus     = bookHisto1D(2, 1, 1);
      _h_mee_Plus     = bookHisto1D(2, 1, 2);
      _h_emm_Plus     = bookHisto1D(2, 1, 3);
      _h_mmm_Plus     = bookHisto1D(2, 1, 4);
      _h_fid_Plus     = bookHisto1D(2, 1, 5);
      _h_eee_Minus    = bookHisto1D(3, 1, 1);
      _h_mee_Minus    = bookHisto1D(3, 1, 2);
      _h_emm_Minus    = bookHisto1D(3, 1, 3);
      _h_mmm_Minus    = bookHisto1D(3, 1, 4);
      _h_fid_Minus    = bookHisto1D(3, 1, 5);
      _h_total        = bookHisto1D(6, 1, 1);
      _h_Njets        = bookHisto1D(8, 1, 1);

    }


    void analyze(const Event& event) {

      const double weight = event.weight();

      const vector<DressedLepton>& dressedleptons = apply<DressedLeptons>(event, "DressedLeptons").dressedLeptons();
      const vector<DressedLepton>& dressedleptonsTotal = apply<DressedLeptons>(event, "DressedLeptonsTotal").dressedLeptons();
      const Particles& neutrinos = apply<PromptFinalState>(event, "Neutrinos").particlesByPt();
      Jets jets = apply<JetAlg>(event, "Jets").jetsByPt( (Cuts::abseta < 4.5) && (Cuts::pT > 25*GeV) );

      if (dressedleptonsTotal.size() < 3 || neutrinos.size() < 1) vetoEvent;

      //---Total PS: assign leptons to W and Z bosons using Resonant shape algorithm
      // NB: This resonant shape algorithm assumes the Standard Model and can therefore
      //     NOT be used for any kind of reinterpretation in terms of new-physics models..

      int i, j, k;
      double MassZ01 = 0., MassZ02 = 0., MassZ12 = 0.;
      double MassW0 = 0., MassW1 = 0., MassW2 = 0.;
      double WeightZ1, WeightZ2, WeightZ3;
      double WeightW1, WeightW2, WeightW3;
      double M1, M2, M3;
      double WeightTotal1, WeightTotal2, WeightTotal3;

      //try Z pair of leptons 01
      if ( (dressedleptonsTotal[0].pid() ==-(dressedleptonsTotal[1].pid())) && (dressedleptonsTotal[2].abspid()==neutrinos[0].abspid()-1)){
        MassZ01 = (dressedleptonsTotal[0].momentum()+dressedleptonsTotal[1].momentum()).mass();
        MassW2 = (dressedleptonsTotal[2].momentum()+neutrinos[0].momentum()).mass();
      }
      //try Z pair of leptons 02
      if ( (dressedleptonsTotal[0].pid()==-(dressedleptonsTotal[2].pid())) && (dressedleptonsTotal[1].abspid()==neutrinos[0].abspid()-1)){
        MassZ02 = (dressedleptonsTotal[0].momentum()+dressedleptonsTotal[2].momentum()).mass();
        MassW1 = (dressedleptonsTotal[1].momentum()+neutrinos[0].momentum()).mass();
      }
      //try Z pair of leptons 12
      if ( (dressedleptonsTotal[1].pid()==-(dressedleptonsTotal[2].pid())) && (dressedleptonsTotal[0].abspid()==neutrinos[0].abspid()-1)){
        MassZ12 = (dressedleptonsTotal[1].momentum()+dressedleptonsTotal[2].momentum()).mass();
        MassW0 = (dressedleptonsTotal[0].momentum()+neutrinos[0].momentum()).mass();
      }
      WeightZ1 = 1/(pow(MassZ01*MassZ01 - MZ_PDG*MZ_PDG,2) + pow(MZ_PDG*GammaZ_PDG,2));
      WeightW1 = 1/(pow(MassW2*MassW2 - MW_PDG*MW_PDG,2) + pow(MW_PDG*GammaW_PDG,2));
      WeightTotal1 = WeightZ1*WeightW1;
      M1 = -1*WeightTotal1;

      WeightZ2 = 1/(pow(MassZ02*MassZ02- MZ_PDG*MZ_PDG,2) + pow(MZ_PDG*GammaZ_PDG,2));
      WeightW2 = 1/(pow(MassW1*MassW1- MW_PDG*MW_PDG,2) + pow(MW_PDG*GammaW_PDG,2));
      WeightTotal2 = WeightZ2*WeightW2;
      M2 = -1*WeightTotal2;

      WeightZ3 = 1/(pow(MassZ12*MassZ12 - MZ_PDG*MZ_PDG,2) + pow(MZ_PDG*GammaZ_PDG,2));
      WeightW3 = 1/(pow(MassW0*MassW0 - MW_PDG*MW_PDG,2) + pow(MW_PDG*GammaW_PDG,2));
      WeightTotal3 = WeightZ3*WeightW3;
      M3 = -1*WeightTotal3;

      if( (M1 < M2 && M1 < M3) || (MassZ01 != 0 && MassW2 != 0 && MassZ02 == 0 && MassZ12 == 0) ){
        i = 0; j = 1; k = 2;
      }
      if((M2 < M1 && M2 < M3) || (MassZ02 != 0 && MassW1 != 0 && MassZ01 == 0 && MassZ12 == 0) ){
        i = 0; j = 2; k = 1;
      }
      if((M3 < M1 && M3 < M2) || (MassZ12 != 0 && MassW0 != 0 && MassZ01 == 0 && MassZ02 == 0) ){
        i = 1; j = 2; k = 0;
      }

      FourMomentum ZbosonTotal   = dressedleptonsTotal[i].momentum()+dressedleptonsTotal[j].momentum();
      if ( ZbosonTotal.mass() >= 66*GeV && ZbosonTotal.mass() <= 116*GeV )  _h_total->fill(13000, weight);

      //---end Total PS


      //---Fiducial PS: assign leptons to W and Z bosons using Resonant shape algorithm
      if (dressedleptons.size() < 3)  vetoEvent;

      int EventType = -1;
      int Nel = 0, Nmu = 0;

      for (const DressedLepton& l : dressedleptons) {
        if (l.abspid() == 11)  ++Nel;
        if (l.abspid() == 13)  ++Nmu;
      }

      if ( (Nel == 3)  && (Nmu==0) )  EventType = 3;
      if ( (Nel == 2)  && (Nmu==1) )  EventType = 2;
      if ( (Nel == 1)  && (Nmu==2) )  EventType = 1;
      if ( (Nel == 0)  && (Nmu==3) )  EventType = 0;

      int EventCharge = -dressedleptons[0].charge() * dressedleptons[1].charge() * dressedleptons[2].charge();

      MassZ01 = 0; MassZ02 = 0; MassZ12 = 0;
      MassW0 = 0;  MassW1 = 0;  MassW2 = 0;

      // try Z pair of leptons 01
      if (dressedleptons[0].pid() == -dressedleptons[1].pid()) {
        MassZ01 = (dressedleptons[0].momentum() + dressedleptons[1].momentum()).mass();
        MassW2 = (dressedleptons[2].momentum() + neutrinos[0].momentum()).mass();
      }
      // try Z pair of leptons 02
      if (dressedleptons[0].pid() == -dressedleptons[2].pid()) {
        MassZ02 = (dressedleptons[0].momentum() + dressedleptons[2].momentum()).mass();
        MassW1 = (dressedleptons[1].momentum() + neutrinos[0].momentum()).mass();
      }
      // try Z pair of leptons 12
      if (dressedleptons[1].pid() == -dressedleptons[2].pid()) {
        MassZ12 = (dressedleptons[1].momentum() + dressedleptons[2].momentum()).mass();
        MassW0 = (dressedleptons[0].momentum() + neutrinos[0].momentum()).mass();
      }
      WeightZ1 = 1/(pow(MassZ01*MassZ01 - MZ_PDG*MZ_PDG,2) + pow(MZ_PDG*GammaZ_PDG,2));
      WeightW1 = 1/(pow(MassW2*MassW2 - MW_PDG*MW_PDG,2) + pow(MW_PDG*GammaW_PDG,2));
      WeightTotal1 = WeightZ1*WeightW1;
      M1 = -1*WeightTotal1;

      WeightZ2 = 1/(pow(MassZ02*MassZ02- MZ_PDG*MZ_PDG,2) + pow(MZ_PDG*GammaZ_PDG,2));
      WeightW2 = 1/(pow(MassW1*MassW1- MW_PDG*MW_PDG,2) + pow(MW_PDG*GammaW_PDG,2));
      WeightTotal2 = WeightZ2*WeightW2;
      M2 = -1*WeightTotal2;

      WeightZ3 = 1/(pow(MassZ12*MassZ12 - MZ_PDG*MZ_PDG,2) + pow(MZ_PDG*GammaZ_PDG,2));
      WeightW3 = 1/(pow(MassW0*MassW0 - MW_PDG*MW_PDG,2) + pow(MW_PDG*GammaW_PDG,2));
      WeightTotal3 = WeightZ3*WeightW3;
      M3 = -1*WeightTotal3;

      if( (M1 < M2 && M1 < M3) || (MassZ01 != 0 && MassW2 != 0 && MassZ02 == 0 && MassZ12 == 0) ) {
        i = 0; j = 1; k = 2;
      }
      if((M2 < M1 && M2 < M3) || (MassZ02 != 0 && MassW1 != 0 && MassZ01 == 0 && MassZ12 == 0) ) {
        i = 0; j = 2; k = 1;
      }
      if((M3 < M1 && M3 < M2) || (MassZ12 != 0 && MassW0 != 0 && MassZ01 == 0 && MassZ02 == 0) ) {
        i = 1; j = 2; k = 0;
      }

      FourMomentum Zlepton1 = dressedleptons[i].momentum();
      FourMomentum Zlepton2 = dressedleptons[j].momentum();
      FourMomentum Wlepton  = dressedleptons[k].momentum();
      FourMomentum Zboson   = dressedleptons[i].momentum()+dressedleptons[j].momentum();

      double Wboson_mT = sqrt( 2 * Wlepton.pT() * neutrinos[0].pt() * (1 - cos(deltaPhi(Wlepton, neutrinos[0]))) );

      if (fabs(Zboson.mass()/GeV - MZ_PDG) >= 10.) vetoEvent;
      if (Wboson_mT <= 30*GeV)                     vetoEvent;
      if (Wlepton.pT() <= 20*GeV)                  vetoEvent;
      if (deltaR(Zlepton1, Zlepton2) < 0.2)        vetoEvent;
      if (deltaR(Zlepton1, Wlepton)  < 0.3)        vetoEvent;
      if (deltaR(Zlepton2, Wlepton)  < 0.3)        vetoEvent;

      if (EventType == 3)  _h_eee->fill(13000., weight);
      if (EventType == 2)  _h_mee->fill(13000., weight);
      if (EventType == 1)  _h_emm->fill(13000., weight);
      if (EventType == 0)  _h_mmm->fill(13000., weight);
      _h_fid->fill(13000, weight);

      if (EventCharge == 1) {
        if (EventType == 3)  _h_eee_Plus->fill(13000., weight);
        if (EventType == 2)  _h_mee_Plus->fill(13000., weight);
        if (EventType == 1)  _h_emm_Plus->fill(13000., weight);
        if (EventType == 0)  _h_mmm_Plus->fill(13000., weight);
        _h_fid_Plus->fill(13000, weight);
      } else {
        if (EventType == 3)  _h_eee_Minus->fill(13000., weight);
        if (EventType == 2)  _h_mee_Minus->fill(13000., weight);
        if (EventType == 1)  _h_emm_Minus->fill(13000., weight);
        if (EventType == 0)  _h_mmm_Minus->fill(13000., weight);
        _h_fid_Minus->fill(13000, weight);
      }

      if (jets.size() < 4)  _h_Njets->fill(jets.size(), weight);
      else  _h_Njets->fill(4, weight);

    }


    void finalize() {

      // Print summary info
      const double xs_pb(crossSection() / picobarn);
      const double xs_fb(crossSection() / femtobarn);
      const double sumw(sumOfWeights());
      const double sf_pb(xs_pb / sumw);
      const double sf_fb(xs_fb / sumw);

      const float totalBR= 4*0.1086*0.033658; // W and Z leptonic branching fractions

      scale(_h_fid,       sf_fb/4.);
      scale(_h_eee,       sf_fb);
      scale(_h_mee,       sf_fb);
      scale(_h_emm,       sf_fb);
      scale(_h_mmm,       sf_fb);
      scale(_h_fid_Plus,  sf_fb/4.);
      scale(_h_eee_Plus,  sf_fb);
      scale(_h_mee_Plus,  sf_fb);
      scale(_h_emm_Plus,  sf_fb);
      scale(_h_mmm_Plus,  sf_fb);
      scale(_h_fid_Minus, sf_fb/4.);
      scale(_h_eee_Minus, sf_fb);
      scale(_h_mee_Minus, sf_fb);
      scale(_h_emm_Minus, sf_fb);
      scale(_h_mmm_Minus, sf_fb);
      scale(_h_Njets, sf_fb/4.);
      scale(_h_total, sf_pb/totalBR);

    }

    //@}


  private:


    /// @name Histograms
    //@{
    Histo1DPtr _h_eee;
    Histo1DPtr _h_mee;
    Histo1DPtr _h_emm;
    Histo1DPtr _h_mmm;
    Histo1DPtr _h_fid;
    Histo1DPtr _h_eee_Plus;
    Histo1DPtr _h_mee_Plus;
    Histo1DPtr _h_emm_Plus;
    Histo1DPtr _h_mmm_Plus;
    Histo1DPtr _h_fid_Plus;
    Histo1DPtr _h_eee_Minus;
    Histo1DPtr _h_mee_Minus;
    Histo1DPtr _h_emm_Minus;
    Histo1DPtr _h_mmm_Minus;
    Histo1DPtr _h_fid_Minus;
    Histo1DPtr _h_total;
    Histo1DPtr _h_Njets;

    //@}

    double MZ_PDG = 91.1876;
    double MW_PDG = 83.385;
    double GammaZ_PDG = 2.4952;
    double GammaW_PDG = 2.085;

  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2016_I1469071);
}