Rivet Analyses Reference

ATLAS_2019_I1720438

Measurement of the $WZ$ production cross section at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1720438
Status: UNVALIDATED
Authors:
  • Eirini Kasimi
  • Emmanuel Sauvan
References:Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • pp -> WZ + X, diboson decays to electrons or muons, data only for single channel

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 36.1 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 $\sigma(W^\pm Z\to\ell^\prime\nu\ell\ell \text{fid.}) = 63.7\pm 3.2$(stat.)$\pm 1.0$(sys.)$\pm 1.4$(lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is 61.5-1.3+1.4 fb. Cross sections for $W^+Z$ and $W^-Z$ production and their ratio are presented as well as differentialcross sections for several kinematic observable. 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. Uses SM neutrino-lepton flavour matching and a resonant shape algorithm assuming the Standard Model, to match the MC-based correction to the fiducial region applied in the paper. This routine is therefore only valid under the assumption of the Standard Model and cannot be used for BSM reinterpretation

Source code: ATLAS_2019_I1720438.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 WZ production cross-section at 13 TeV
  class ATLAS_2019_I1720438 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1720438);

    /// @name Analysis methods
    //@{


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

      PromptFinalState photons(Cuts::abspid == PID::PHOTON);

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

      // Prompt 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");

      // Muons
      PromptFinalState bare_mu(Cuts::abspid == PID::MUON, true); // true = use muons from prompt tau decays
      DressedLeptons all_dressed_mu(photons, bare_mu, 0.1, Cuts::abseta < 2.5, true);

      // Electrons
      PromptFinalState bare_el(Cuts::abspid == PID::ELECTRON, true); // true = use electrons from prompt tau decays
      DressedLeptons all_dressed_el(photons, bare_el, 0.1, Cuts::abseta < 2.5, true);

      //Jet forming
      VetoedFinalState vfs(FinalState(Cuts::abseta < 5.0));
      vfs.addVetoOnThisFinalState(all_dressed_el);
      vfs.addVetoOnThisFinalState(all_dressed_mu);
	      
      FastJets jets(vfs, FastJets::ANTIKT, 0.4, JetAlg::Muons::ALL, JetAlg::Invisibles::DECAY);
      declare(jets, "Jets");

      // Book auxiliary histograms
      book(_h["pTZ"],    "_pTZ",    refData( 8, 1, 1));
      book(_h["pTW"],    "_pTW",    refData(10, 1, 1));
      book(_h["mTWZ"],   "_mTWZ",   refData(12, 1, 1));
      book(_h["dPhiWZ"], "_dPhiWZ", refData(14, 1, 1));
      book(_h["pTv"],    "_pTV",    refData(16, 1, 1));
      book(_h["dRapWZ"], "_drapWZ", refData(18, 1, 1));
      book(_h["Njets"],  "_njets",  refData(20, 1, 1)); 
      book(_h["Mjj"],    "_mjj",    refData(22, 1, 1)); 

      // book output bar charts
      book(_s["pTZ"],     8, 1, 1);
      book(_s["pTW"],    10, 1, 1);
      book(_s["mTWZ"],   12, 1, 1);
      book(_s["dPhiWZ"], 14, 1, 1);
      book(_s["pTv"],    16, 1, 1);
      book(_s["dRapWZ"], 18, 1, 1);
      book(_s["Njets"],  20, 1, 1); 
      book(_s["Mjj"],    22, 1, 1); 

    }


    void analyze(const Event& event) {

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

      //---Fiducial PS: assign leptons to W and Z bosons using Resonant shape algorithm
       if (dressedleptons.size() < 3 || neutrinos.size() < 1) vetoEvent;                                                              

      //--- count num of electrons and muons
      int Nel = 0, Nmu = 0;
      for (const Particle& l : dressedleptons) {
        if (l.abspid() == 11)  ++Nel;
        if (l.abspid() == 13)  ++Nmu;
      }

      int icomb=0;
      // try Z pair of leptons 01                                                              
    if ( (dressedleptons[0].pid() ==-(dressedleptons[1].pid()))  && (dressedleptons[2].pid()*neutrinos[0].pid()< 0) && (dressedleptons[2].abspid()==neutrinos[0].abspid()-1)) {
        MassZ01 = (dressedleptons[0].momentum() + dressedleptons[1].momentum()).mass();
        MassW2 = (dressedleptons[2].momentum() + neutrinos[0].momentum()).mass();
        icomb = 1;
      }

      // try Z pair of leptons 02
      if ( (dressedleptons[0].pid()==-(dressedleptons[2].pid()))  && (dressedleptons[1].pid()*neutrinos[0].pid()< 0) && (dressedleptons[1].abspid()==neutrinos[0].abspid()-1)) {
        MassZ02 = (dressedleptons[0].momentum() + dressedleptons[2].momentum()).mass();
        MassW1 = (dressedleptons[1].momentum() + neutrinos[0].momentum()).mass();
        icomb = 2;
      }
      // try Z pair of leptons 12
      if ( (dressedleptons[1].pid()==-(dressedleptons[2].pid())) && (dressedleptons[0].pid()*neutrinos[0].pid()< 0) && (dressedleptons[0].abspid()==neutrinos[0].abspid()-1)) {
        MassZ12 = (dressedleptons[1].momentum() + dressedleptons[2].momentum()).mass();
        MassW0 = (dressedleptons[0].momentum() + neutrinos[0].momentum()).mass();
        icomb = 3;
      }
 
      if (icomb<=0)  vetoEvent;


      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].mom();
      FourMomentum Zlepton2 = dressedleptons[j].mom();
      FourMomentum Wlepton  = dressedleptons[k].mom();
      FourMomentum Zboson   = dressedleptons[i].mom()+dressedleptons[j].mom();
      FourMomentum Wboson   = dressedleptons[k].mom()+neutrinos[0].mom();

     double cosLepNeut;
     double Wboson_mT = 0;
   	 double norm = Wlepton.pT() * neutrinos[0].pt();
	   if (norm != 0) {
	     cosLepNeut = ( Wlepton.px()*neutrinos[0].px() + Wlepton.py()*neutrinos[0].py() )/norm;
	     if ( 1-cosLepNeut >= 0 )  Wboson_mT = sqrt( 2 * Wlepton.pT() * neutrinos[0].pt() * (1-cosLepNeut ) );
	   }

      //---- CUTS (based on Table 1 WZ: 36.1 fb-1)----//
      if (Wlepton.pT() <= 20*GeV || Zlepton1.pT() <= 15*GeV || Zlepton2.pT() <= 15*GeV)  vetoEvent;      
      if (Wlepton.abseta() >= 2.5 || Zlepton1.abseta() >= 2.5 || Zlepton2.abseta() >= 2.5)  vetoEvent;
      if (fabs(Zboson.mass()/GeV - MZ_PDG) >= 10.) vetoEvent;
      if (Wboson_mT <= 30*GeV)                     vetoEvent;
      if (deltaR(Zlepton1, Zlepton2) <= 0.2)       vetoEvent;
      if (deltaR(Zlepton1, Wlepton)  <= 0.3)       vetoEvent;
      if (deltaR(Zlepton2, Wlepton)  <= 0.3)       vetoEvent;

      double pTZ = Zboson.pT()/GeV;
      double WZ_pt = (Zlepton1.pt() + Zlepton2.pt() + Wlepton.pt() + neutrinos[0].pt())/GeV;
      double WZ_px = (Zlepton1.px() + Zlepton2.px() + Wlepton.px() + neutrinos[0].px())/GeV;
      double WZ_py = (Zlepton1.py() + Zlepton2.py() + Wlepton.py() + neutrinos[0].py())/GeV;
      double mTWZ = sqrt( pow(WZ_pt, 2) - ( pow(WZ_px, 2) + pow(WZ_py,2) ));

      double dPhiWZTruth = acos(cos(Zboson.phi()-Wboson.phi()));
      double pTW = Wboson.pT()/GeV;
      double pTv = neutrinos[0].pT()/GeV;
      double AbsDeltay = fabs(Zboson.rapidity()-Wlepton.rapidity());

      ifilter_discard(jets, [&](const Jet& j) {
        return deltaR(j, Zlepton1) < 0.3 || deltaR(j, Zlepton2) < 0.3 || deltaR(j, Wlepton) < 0.3;
      });

      size_t njets = jets.size()>5? 5 : jets.size();
      _h["Njets"]->fill(njets);

      if (njets > 1) {
        double mjj = (jets[0].mom() + jets[1].mom()).mass()/GeV;
        if (mjj > 800.)  mjj = 800.;
        _h["Mjj"]->fill(mjj);
      }

      if (pTZ > 220.) pTZ = 220.;
      _h["pTZ"]->fill(pTZ);

      if (pTW > 220.)  pTW = 220.;
      _h["pTW"]->fill(pTW);

      if (mTWZ > 600.)  mTWZ = 600.;
      _h["mTWZ"]->fill(mTWZ);

      _h["dPhiWZ"]->fill(dPhiWZTruth);

      if (pTv > 90.)  pTv = 90.;
      _h["pTv"]->fill(pTv);

      _h["dRapWZ"]->fill(AbsDeltay);

    }


    void finalize() {

      scale(_h, 0.25 * crossSectionPerEvent() / femtobarn); // data values are for _single_ lepton channel
      // unfortunately, no differential cross-sections were measured in this analysis
      for (auto &item : _h)  barchart(item.second, _s[item.first]);

    }

    //@}


  private:


    /// @name Histograms
    //@{
    
    map<string, Histo1DPtr> _h;
    map<string, Scatter2DPtr> _s;

    //@}

    double MZ_PDG = 91.1876;
    double MW_PDG = 80.385;
    double GammaZ_PDG = 2.4952;
    double GammaW_PDG = 2.085;

  };

  // The hook for the plugin system
  RIVET_DECLARE_PLUGIN(ATLAS_2019_I1720438);
}

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