Rivet analyses

Z(vv)+gamma measurement at 13 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1698006

Status: VALIDATED

Authors: - Jon Butterworth - Michail Sokratis - Yoran Yeh

References: - Expt page: ATLAS-STDM-2017-18 - JHEP 12 (2018) 010 - 10.1007/JHEP12(2018)010 - arXiv: 1810.04995

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - p + p -> Z0 nu nubar gamma at 13 TeV

The production of Z bosons in association with a high-energy photon (Z$\gamma$ production) is studied in the neutrino decay channel of the Z boson using pp collisions at $\sqrt s$ = 13 TeV. The analysis uses a data sample with an integrated luminosity of 36.1 fb-1 collected by the ATLAS detector at the LHC in 2015 and 2016. Candidate Z$\gamma$ events with invisible decays of the Z boson are selected by requiring significant transverse momentum (pT) of the dineutrino system in conjunction with a single isolated photon with large transverse energy (ET). The rate of Z$\gamma$ production is measured as a function of photon ET, dineutrino system pT and jet multiplicity. Evidence of anomalous triple gauge-boson couplings is sought in Z$\gamma$ production with photo ET greater than 600 GeV. No excess is observed relative to the Standard Model expectation, and upper limits are set on the strength of ZZ$\gamma$ and Z$\gamma\gamma$ couplings.

Source code:`ATLAS_2018_I1698006.cc`

#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/InvisibleFinalState.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {


  /// @brief ATLAS pTmiss+gamma measurement at 13 TeV
  class ATLAS_2018_I1698006 : public Analysis {
  public:

    /// Default constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2018_I1698006);


    /// @name Analysis methods
    /// @{
    void init() {

      // Get options
      // Default (OFF) uses the extended phase space of the paper.
      // LVETO ON will add an additonal lepton veto to reject non-Zgamma events
      // (for conservative BSM limits, for example).
      _mode = 0;
      if (getOption("LVETO") == "ON") _mode = 1;

      //prompt photons
      const Cut photoncut = Cuts::abspid == PID::PHOTON && Cuts::Et > 150 * GeV && Cuts::abseta < 2.37;
      const PromptFinalState photon_fs(photoncut);
      declare(photon_fs, "Photons");

      //missing energy (prompt neutrinos)
      declare(InvisibleFinalState(OnlyPrompt::YES), "MET");

      if (_mode == 1) {
        FinalState allLeps(Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON);
        FinalState photons(Cuts::abspid == PID::PHOTON);
        PromptFinalState promptLeps(allLeps);
        Cut dressedLep_cuts = (Cuts::abseta < 2.7) && (Cuts::pT > 7 * GeV);
        LeptonFinder dressedLeps(promptLeps, photons, 0.1, dressedLep_cuts);
        declare(dressedLeps, "dressedLeptons");
      }

      //jets. run the jet finder on a final state without the prompt photons, and without neutrinos or muons
      VetoedFinalState jet_fs(Cuts::abseta > 4.5);
      jet_fs.addVetoOnThisFinalState(photon_fs);
      FastJets fastjets(jet_fs, JetAlg::ANTIKT, 0.4, JetMuons::NONE, JetInvisibles::NONE);
      declare(fastjets, "Jets");


      //books histograms
      //fig.4a
      book(_h["Et_inc"], 2, 1, 1);
      //fig.4b
      book(_h["Et_exc"], 3, 1, 1);
      //fig.5a
      book(_h["pT_inc"], 4, 1, 1);
      //fig.5b
      book(_h["pT_exc"], 5, 1, 1);
      //fig.6
      book(_h["Njets"], 6, 1, 1);
    }


    void analyze(const Event& event) {

      const Particles& photons = apply<PromptFinalState>(event, "Photons").particlesByPt();
      const Jets& jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 50 * GeV);
      const FinalState& metfs = apply<InvisibleFinalState>(event, "MET");
      Vector3 met_vec;
      for (const Particle& p : metfs.particles()) met_vec += p.mom().perpVec();


      if (_mode == 1) {
        const DressedLeptons& dressedLeptons = apply<LeptonFinder>(event, "dressedLeptons").dressedLeptons();
        if (dressedLeptons.size() > 0) vetoEvent;
      }

      //Nγ==1 and Emiss > 150 GeV
      if (met_vec.mod() > 150 * GeV && photons.size() == 1) {

        //inclusive case (Njet>=0)
        //if (jets.size()>=0){ //< size is always >= 0
        {
          bool dR_veto = any(jets, DeltaRLess(photons[0], 0.3));
          if (not dR_veto) {
            double Et_photon = photons[0].Et() / GeV;
            _h["Et_inc"]->fill(Et_photon);
            //fill in missing energy (neutrino) pT histogram (inclusive)
            _h["pT_inc"]->fill(met_vec.mod() / GeV);
          }
        }

        //exclusive case (Njet==0)
        if (jets.size() == 0) {
          double Et_photon = photons[0].Et() / GeV;
          _h["Et_exc"]->fill(Et_photon);
          //fill in missing energy (neutrino) pT histogram (exclusive)
          _h["pT_exc"]->fill(met_vec.mod() / GeV);
        }

        _h["Njets"]->fill(jets.size());
      }
    }


    void finalize() {
      const double sf = crossSection() / femtobarn / sumOfWeights();
      scale(_h, sf);
    }

    /// @}


  private:

    map<string, Histo1DPtr> _h;

    size_t _mode;
  };


  RIVET_DECLARE_PLUGIN(ATLAS_2018_I1698006);

}

Rivet analyses

Z(vv)+gamma measurement at 13 TeV

Source code:ATLAS_2018_I1698006.cc

Source code:`ATLAS_2018_I1698006.cc`