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ATLAS_2016_I1448301

$Z \gamma (\gamma)$ cross sections at 8 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1448301
Status: VALIDATED
Authors:
  • Hulin Wang
  • Evgeny Soldatov
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • p + p -> e+ e- gamma (gamma) at 8 TeV

The production of $Z$ bosons with one or two isolated high-energy photons is studied using pp collisions at $\sqrt{s}=8$ TeV. The analyses use a data sample with an integrated luminosity of 20.3 fb${}^{-1}$ collected by the ATLAS detector during the 2012 LHC data taking. The $Z\gamma$ and $Z\gamma\gamma$ production cross sections are measured with leptonic ($e^+e^-$, $\mu^+\mu^-$, $\nu\bar{\nu}$) decays of the Z boson, in extended fiducial regions defined in terms of the lepton and photon acceptance. They are then compared to cross-section predictions from the Standard Model, where the sources of the photons are radiation off initial-state quarks and radiative Z-boson decay to charged leptons, and from fragmentation of final-state quarks and gluons into photons. The yields of events with photon transverse energy $E_\text{T}>250$ GeV from $\ell^+\ell^-\gamma$ events and with $E_\text{T}>400$ GeV from $\nu\bar{\nu}\gamma$ events are used to search for anomalous triple gauge-boson couplings $ZZ\gamma$ and $Z\gamma\gamma$. The yields of events with diphoton invariant mass $m_{\gamma\gamma}>200$ GeV from $\ell^+\ell^-\gamma\gamma$ events and with $m_{\gamma\gamma}>300$ GeV from $\nu\bar{\nu}\gamma\gamma$ events are used to search for anomalous quartic gauge-boson couplings $ZZ\gamma\gamma$ and $Z\gamma\gamma\gamma$. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings. The lepton channel can be specified by using the relevant LMODE (EL, MU, NU, LL). The default plugin will fill all of them with any events passing the cuts. NU will do only the MET channels, EL & MU will do only the electron or muon and will populate the combined plots assuming charged lepton universality. LL with do on the electron and muon but will populate the combined plots with the average of the two.

Source code: ATLAS_2016_I1448301.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/VisibleFinalState.hh"

namespace Rivet {


  /// @brief Z/gamma cross section measurement at 8 TeV
  class ATLAS_2016_I1448301 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2016_I1448301);


    /// @name Analysis methods
    //@{

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

      // Get options from the new option system
      // Default tries to fill everything
      // NU fills only the MET plots
      // EL fills only the Electron plots and combined plots assuming lepton univerality
      // MU fills only the Muon plots and combined plots assuming lepton univerality
      // LL fills electron and Muon plots and combined plots from correct average
      _mode = 0;
      if ( getOption("LMODE") == "NU" ) _mode = 1;
      if ( getOption("LMODE") == "EL" ) _mode = 2;
      if ( getOption("LMODE") == "MU" ) _mode = 3;
      if ( getOption("LMODE") == "LL" ) _mode = 4;

      // Prompt photons
      const Cut photoncut = Cuts::abspid == PID::PHOTON && Cuts::pT > 15*GeV && Cuts::abseta < 2.37;
      PromptFinalState photon_fs(photoncut);
      declare(photon_fs, "Photons");

      // Prompt leptons
      const PromptFinalState bareelectron_fs = Cuts::abspid == PID::ELECTRON;
      const PromptFinalState baremuon_fs = Cuts::abspid == PID::MUON;

      // Dressed leptons
      const IdentifiedFinalState allphoton_fs(PID::PHOTON); // photons used for lepton dressing
      const Cut leptoncut = Cuts::pT > 25*GeV && Cuts::abseta < 2.47;
      const DressedLeptons dressedelectron_fs(allphoton_fs, bareelectron_fs, 0.1, leptoncut, true); // use *all* photons for lepton dressing
      const DressedLeptons dressedmuon_fs(allphoton_fs, baremuon_fs, 0.1, leptoncut, true); // use *all* photons for lepton dressing

      declare(dressedelectron_fs, "Electrons");
      declare(dressedmuon_fs, "Muons");

      // MET (prompt neutrinos)
      VetoedFinalState ivfs;
      ivfs.addVetoOnThisFinalState(VisibleFinalState());
      declare(PromptFinalState(ivfs), "MET");

      // Jets
      VetoedFinalState jet_fs;
      jet_fs.vetoNeutrinos();
      jet_fs.addVetoPairId(PID::MUON);
      const FastJets fastjets(jet_fs, FastJets::ANTIKT, 0.4);
      declare(fastjets, "Jets");

      // Histograms

      // MET
      if (_mode == 0 || _mode == 1){
	_h["vvg"]     = bookHisto1D( 2, 1, 1);
	_h["vvgg"]    = bookHisto1D( 4, 1, 1);
	_h["pT"]      = bookHisto1D( 7, 1, 1);
	_h["pT_0jet"] = bookHisto1D( 8, 1, 1);
      }
	
      // always book e and mu in charged lepton modes; there are sometimes 4 leptons.
      if (_mode != 1){
	// electron
	_h["eeg"]       = bookHisto1D( 1, 1, 1);
	_h["eegg"]      = bookHisto1D( 3, 1, 1);
	// muon
	_h["mmg"]       = bookHisto1D( 1, 1, 2);
	_h["mmgg"]      = bookHisto1D( 3, 1, 2);

	// combined
	_h["llgg"] = bookHisto1D( 3, 1, 3);
	_h["llg"]  = bookHisto1D( 1, 1, 3);
	_h["pT"]       = bookHisto1D( 5, 1, 1);
	_h["pT_0jet"]  = bookHisto1D( 6, 1, 1);
	_h["M"]        = bookHisto1D( 9, 1, 1);
	_h["M_0jet"]   = bookHisto1D(10, 1, 1);
	_h["Njets"]    = bookHisto1D(11, 1, 1);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {

      const double weight = event.weight();

      // Get objects
      vector<DressedLepton> electrons = apply<DressedLeptons>(event, "Electrons").dressedLeptons();
      vector<DressedLepton> muons = apply<DressedLeptons>(event, "Muons").dressedLeptons();

      const Particles& photons = apply<PromptFinalState>(event, "Photons").particlesByPt();
      const Jets jets = apply<FastJets>(event, "Jets").jetsByPt();

      const FinalState& metfs = apply<PromptFinalState>(event, "MET");
      Vector3 met_vec;
      for (const Particle& p : metfs.particles()) met_vec += p.mom().perpVec();
      
      if (met_vec.mod() >= 100*GeV && !photons.empty() && _mode < 2){

	if (photons.size() > 1) { // nu nu y y
	
	  bool yy_veto = false;
	  yy_veto |= photons[0].pT() < 22*GeV;
	  yy_veto |= photons[1].pT() < 22*GeV;
	  yy_veto |= met_vec.mod() < 110*GeV;
	  const double yyPhi = (photons[0].momentum() + photons[1].momentum()).phi();
	  yy_veto |= fabs(yyPhi - met_vec.phi()) < 2.62 || fabs(yyPhi - met_vec.phi()) > 3.66;
	  yy_veto |= deltaR(photons[0], photons[1]) < 0.4;
	  
	  // Photon isolation calculated by jets, count jets
	  Jet ph0_jet, ph1_jet;
	  double min_dR_ph0_jet = 999., min_dR_ph1_jet = 999.;
	  size_t njets = 0;
	  for (const Jet& j : jets) {
	    if (j.pT() > 30*GeV && j.abseta() < 4.5) {
	      if (deltaR(j, photons[0]) > 0.3 && deltaR(j, photons[1]) > 0.3)  ++njets;
	    }
	    if (deltaR(j, photons[0]) < min_dR_ph0_jet) {
	      min_dR_ph0_jet = deltaR(j, photons[0]);
	      ph0_jet = j;
	    }
	    if (deltaR(j, photons[1]) < min_dR_ph1_jet) {
	      min_dR_ph1_jet = deltaR(j, photons[1]);
	      ph1_jet = j;
	    }
	  }
	  double photon0iso = 0., photon1iso = 0.;
	  if (min_dR_ph0_jet < 0.4)  photon0iso = ph0_jet.pT() - photons[0].pT();
	  if (min_dR_ph1_jet < 0.4)  photon1iso = ph1_jet.pT() - photons[1].pT();
	  yy_veto |= photon0iso/photons[0].pT() > 0.5;
	  yy_veto |= photon1iso/photons[1].pT() > 0.5;
	  
	  if (!yy_veto) {
	    _h["vvgg"]->fill(0.5, weight);
	    if (!njets)  _h["vvgg"]->fill(1.5, weight);
	  }
	} // end of nu nu y y section
      
      
	if ((photons[0].pT() >= 130*GeV)  &&
	    (fabs(fabs(deltaPhi(photons[0], met_vec)) - 3.14) >= 1.57)) {
      
	  // Photon isolation calculated by jets, count jets
	  Jet ph_jet;
	  double min_dR_ph_jet = 999.;
	  size_t njets = 0;
	  for (const Jet& j : jets) {
	    if (j.pT() > 30*GeV && j.abseta() < 4.5) {
	      if (deltaR(j, photons[0]) > 0.3)  ++njets;
	    }
	    if (deltaR(j, photons[0]) < min_dR_ph_jet) {
	      min_dR_ph_jet = deltaR(j, photons[0]);
	      ph_jet = j;
	    }
	  }
	  double photoniso = 0;
	  if (min_dR_ph_jet < 0.4)  photoniso = ph_jet.pT() - photons[0].pT();
	  if (photoniso/photons[0].pT() > 0.5)  vetoEvent;
	  
	  const double pTgamma = photons[0].pT()/GeV;
	  _h["pT"]->fill(pTgamma, weight);
	  _h["vvg"]->fill(0.5, weight);
	  if (!njets) {
	    _h["vvg"]->fill(1.5, weight);
	    _h["pT_0jet"]->fill(pTgamma, weight);
	  }
	  	  
	}
      }  // end of nu nu y (y) section

      // Dilepton candidate
      bool el = false;
      if ( (_mode != 1) &&
	   (( electrons.size() >= 2 && _mode != 3 ) || 
	    ( muons.size()     >= 2 && _mode != 2 ) )) {

	vector<DressedLepton> lep_p, lep_m;

	// Sort the dressed leptons by pt
	if (electrons.size() >= 2) {
	  el = true;
	  std::sort(electrons.begin(), electrons.end(), cmpMomByPt);
	  for (const DressedLepton& lep : electrons) {
	    if (lep.charge() > 0.)  lep_p.push_back(lep);
	    if (lep.charge() < 0.)  lep_m.push_back(lep);
	  }	
	} else {
	  std::sort(muons.begin(), muons.end(), cmpMomByPt);
	  for (const DressedLepton& lep : muons) {
	    if (lep.charge() > 0.)  lep_p.push_back(lep);
	    if (lep.charge() < 0.)  lep_m.push_back(lep);
	  }	
	}
      

	if (!lep_p.empty() && !lep_m.empty() &&
	    (lep_p[0].abspid() == lep_m[0].abspid()) &&
	    ((lep_p[0].momentum() + lep_m[0].momentum()).mass() >= 40*GeV)){

	  // Photon lepton overlap removal
	  if (photons.empty())  vetoEvent;
	  
	  if (photons.size() > 1) {
	    
	    bool veto = false;
	    veto |= deltaR(photons[0], lep_p[0]) < 0.4;
	    veto |= deltaR(photons[0], lep_m[0]) < 0.4;
	    veto |= deltaR(photons[1], lep_p[0]) < 0.4;
	    veto |= deltaR(photons[1], lep_m[0]) < 0.4;
	    veto |= deltaR(photons[0], photons[1]) < 0.4;
	    
	    Jet ph0_jet, ph1_jet;
	    double min_dR_ph0_jet = 999., min_dR_ph1_jet=999.;
	    int njets = 0;
	    for (const Jet& j : jets){
	      if (j.pT() > 30*GeV && j.abseta() < 4.5) {
		if (deltaR(j, lep_p[0]) > 0.3 && deltaR(j, lep_m[0]) > 0.3) {
		  if (deltaR(j, photons[0]) > 0.3 && deltaR(j, photons[1]) > 0.3 )  ++njets;
		}
	      }
	      if (deltaR(j, photons[0]) < min_dR_ph0_jet) {
		min_dR_ph0_jet = deltaR(j, photons[0]);
		ph0_jet = j;
	      }
	      if (deltaR(j, photons[1]) < min_dR_ph1_jet) {
		min_dR_ph1_jet = deltaR(j, photons[1]);
		ph1_jet = j;
	      }
	    }
	    double photon0iso = 0, photon1iso = 0;
	    if (min_dR_ph0_jet < 0.4) photon0iso = ph0_jet.pT() - photons[0].pT();
	    if (min_dR_ph1_jet < 0.4) photon1iso = ph1_jet.pT() - photons[1].pT();
	    veto |= photon0iso/photons[0].pT() > 0.5;
	    veto |= photon1iso/photons[1].pT() > 0.5;
	    
	    // Fill plots
	    // ee and mm need doing.
	    if (!veto) {
	      _h["llgg"]->fill(0.5, weight);
	      if (el) {
		_h["eegg"]->fill(0.5, weight);
	      } else {
		_h["mmgg"]->fill(0.5, weight);
	      }

	      if (!njets) {
		_h["llgg"]->fill(1.5, weight);
		if (el) {
		  _h["eegg"]->fill(1.5, weight);
		} else {
		  _h["mmgg"]->fill(1.5, weight);
		}
	      }
	    }
	  }
	  
	  if (deltaR(photons[0], lep_p[0]) < 0.7)  vetoEvent;
	  if (deltaR(photons[0], lep_m[0]) < 0.7)  vetoEvent;
	  
	  // Photon isolation calculated by jets, count jets
	  Jet ph_jet;
	  double min_dR_ph_jet = 999.;
	  size_t njets = 0;
	  for (const Jet& j : jets) {
	    if (j.pT() > 30*GeV && j.abseta() < 4.5) {
	      if (deltaR(j, lep_p[0]) > 0.3 && deltaR(j, lep_m[0]) > 0.3 && deltaR(j, photons[0]) > 0.3)  ++njets;
	    }
	    if (deltaR(j, photons[0]) < min_dR_ph_jet) {
	      min_dR_ph_jet = deltaR(j, photons[0]);
	      ph_jet = j;
	    }
	  }
	  
	  double photoniso = 0;
	  if (min_dR_ph_jet < 0.4)  photoniso = ph_jet.pT() - photons[0].pT();
	  if (photoniso/photons[0].pT() > 0.5)  vetoEvent;
	  
	  
	  // Fill plots
	  const double pTgamma = photons[0].pT()/GeV;
	  const double mllgamma = (lep_p[0].momentum() + lep_m[0].momentum() + photons[0].momentum()).mass()/GeV;
	  
	  _h["pT"]->fill(pTgamma,  weight);
	  _h["M"]->fill(mllgamma, weight);
	  _h["Njets"]->fill(njets < 3? njets : 3, weight);
	  
	  _h["llg"]->fill(0.5, weight);
	  if (el) {
	    _h["eeg"]->fill(0.5, weight);
	  } else {
	    _h["eeg"]->fill(0.5, weight);
	  }

	  if (!njets) {
	    _h["pT_0jet"]->fill(pTgamma, weight);
	    _h["M_0jet"]->fill(mllgamma, weight);
	    _h["llg"]->fill(1.5, weight);
	    if (el) {
	      _h["eeg"]->fill(1.5, weight);
	    } else {
	      _h["mmg"]->fill(1.5, weight);
	    }
	  }
	}
      }
    } // end of analysis


    /// Normalise histograms etc., after the run
    void finalize() {
      const double sf = crossSection()/femtobarn/sumOfWeights();
      for (const auto& kv : _h) scale(kv.second, sf);
      // if we are running both e and mu, the combined lepton histos
      // need to be divided by two to get the average
      if (_mode == 0 || _mode == 4){
	scale(_h["llgg"], 0.5);
	scale(_h["llg"], 0.5);
	scale(_h["pT"], 0.5);
	scale(_h["pT_0jet"], 0.5);
	scale(_h["M"], 0.5);
	scale(_h["M_0jet"], 0.5);
	scale(_h["Njets"], 0.5);
      }
    }

    //@}


  protected:

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

  private:

    /// Histograms
    map<string, Histo1DPtr> _h;

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2016_I1448301);

}