Rivet analyses

title: ATLAS_2023_I2663725

VBS Zy production at 13 TeV

Experiment: ATLAS (LHC)

Inspire ID: 2663725

Status: VALIDATED

Authors: - Qibin Liu - Gitanjali Poddar - Narei Lorenzo Martinez

References: - arXiv: 2305.19142 - Expt page: ATLAS-STDM-2018-36

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - Electroweak Zy + 2jet production

This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a $Z\gamma$ pair in association with two jets. The analysis uses 140 fb${}^{-1}$ of LHC proton-proton collision data taken at $\sqrt{s}=13$ TeV recorded by the ATLAS detector during the years 2015-2018. Events with a $Z$ boson candidate decaying into either an $e^+e^-$ or $\mu^+\mu^-$ pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and a large rapidity gap between the two jets and is measured with an observed and expected significance well above five standard deviations. The fiducial $pp \to Z\gamma jj$ cross-section for the electroweak production is measured to be $3.6 \pm 0.5$ fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be $16.8+2.0-1.8$ fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with partoni-shower Monte Carlo simulations. Good agreement is observed between data and predictions.

Source code:ATLAS_2023_I2663725.cc

```c++ // -- C++ --

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 VBS Zy production at 13 TeV class ATLAS_2023_I2663725 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2023_I2663725);

/// @name Analysis methods
//@{
/// Book histograms and initialise projections before the run
void init() {

  FinalState fs;
  // Prompt photons
  const PromptFinalState photon_fs(Cuts::abspid == PID::PHOTON && Cuts::pT > 25 * GeV
                                   && Cuts::abseta < 2.37);
  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 FinalState allphoton_fs(Cuts::abspid == PID::PHOTON);
  const Cut leptoncut = Cuts::pT > 20 * GeV && Cuts::abseta < 2.47;
  // use *all* photons for dressing
  const LeptonFinder dressedelectron_fs(bareelectron_fs, allphoton_fs, 0.1, leptoncut);
  const LeptonFinder dressedmuon_fs(baremuon_fs, allphoton_fs, 0.1, leptoncut);

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

  // FS excluding the leading photon
  VetoedFinalState vfs;
  vfs.addVetoOnThisFinalState(photon_fs);
  vfs.addVetoOnThisFinalState(dressedmuon_fs);
  vfs.addVetoOnThisFinalState(InvisibleFinalState());
  declare(vfs, "isolatedFS");

  VetoedFinalState hadrons(FinalState(Cuts::abseta < 4.4));
  hadrons.addVetoOnThisFinalState(dressedelectron_fs);
  hadrons.addVetoOnThisFinalState(dressedmuon_fs);

  // Jets
  FastJets jets(hadrons, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::DECAY);
  declare(jets, "jets");

  // Histograms
  size_t idx = 0;
  const vector<string> dists{"pTlep1", "pTy", "pTjet1", "pTll", "pTlly", "mjj", "dRap", "dPhi", "cent"};
  for (const string& reg : vector<string>{"", "_ext"}) {
    for (const string& obs : dists) {
      if (reg == "" && (obs == "pTll" || obs == "cent")) continue;
      book(_h[obs + reg], ++idx, 1, 1);
    }
  }
}

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

  // Sort the dressed leptons by pt
  Particles electrons = apply<LeptonFinder>(event, "Electrons").particlesByPt();
  Particles muons = apply<LeptonFinder>(event, "Muons").particlesByPt();

  if (electrons.size() < 2 && muons.size() < 2) vetoEvent;

  Particles lep;
  if (electrons.size() >= 2) {
    lep.push_back(electrons[0]);
    lep.push_back(electrons[1]);
  }
  else if (muons.size() >= 2) {
    lep.push_back(muons[0]);
    lep.push_back(muons[1]);
  }
  if (lep.size() != 2) vetoEvent;
  if (lep[0].pT() < 30 * GeV) vetoEvent;

  const double mll = (lep[0].momentum() + lep[1].momentum()).mass();

  Particles photons = apply<PromptFinalState>(event, "Photons").particlesByPt();
  if (photons.empty()) vetoEvent;

  idiscardIfAnyDeltaRLess(photons, electrons, 0.4);
  idiscardIfAnyDeltaRLess(photons, muons, 0.4);

  Particles selectedPh;
  Particles fs = apply<VetoedFinalState>(event, "isolatedFS").particles();
  for (const Particle& ph : photons) {
    // check photon isolation
    double coneEnergy(0.0);
    for (const Particle& p : fs) {
      if (deltaR(ph, p) < 0.2) coneEnergy += p.Et(); // etcone20
    }
    if (coneEnergy / ph.pT() > 0.07) continue;
    selectedPh += ph;
  }

  if (selectedPh.size() < 1) vetoEvent;

  // Get jets
  const Cut jetscut = (Cuts::pT > 25 * GeV && Cuts::absrap < 4.4);
  Jets jetsMix = apply<FastJets>(event, "jets").jetsByPt(jetscut);

  idiscardIfAnyDeltaRLess(jetsMix, photons, 0.4);
  idiscardIfAnyDeltaRLess(jetsMix, electrons, 0.3);
  idiscardIfAnyDeltaRLess(jetsMix, muons, 0.3);

  // Jet multiplicity
  const size_t njets = jetsMix.size();
  if (njets < 2) vetoEvent;

  if (jetsMix[1].pT() < 50 * GeV) vetoEvent; // sorted by pT, must all > 50GeV

  if (mll < 40 * GeV) vetoEvent;

  const FourMomentum lly_system = lep[0].momentum() + lep[1].momentum() + selectedPh[0].momentum();
  const double mlly = lly_system.mass();
  if (mll + mlly <= 182 * GeV) vetoEvent;

  // other complex cuts
  const FourMomentum jj_system = jetsMix[0].momentum() + jetsMix[1].momentum();
  const double mjj = jj_system.mass();
  if (mjj < 150 * GeV) vetoEvent;

  const double Dyjj = fabs(deltaRap(jetsMix[0].momentum(), jetsMix[1].momentum()));
  if (Dyjj < 1) vetoEvent;

  const double j1rap = jetsMix[0].rap();
  const double j2rap = jetsMix[1].rap();

  const double Centrality = fabs((lly_system.rap() - 0.5 * (j1rap + j2rap)) / (j1rap - j2rap));
  if (Centrality > 5) vetoEvent;

  size_t njGap = 0;
  for (size_t i = 2; i < njets; ++i) {
    const double jrap = jetsMix[i].rap();
    if ((jrap < j1rap && jrap > j2rap) || (jrap < j2rap && jrap > j1rap)) ++njGap;
  }
  if (njGap > 0) vetoEvent;

  // now start to log hist
  // first we select the extended SR
  if (Centrality > 0.4) vetoEvent;

  _h["pTjet1_ext"]->fill(jetsMix[0].pT() / GeV);
  _h["pTy_ext"]->fill(selectedPh[0].pT() / GeV);
  _h["pTlep1_ext"]->fill(lep[0].pT() / GeV);
  _h["pTll_ext"]->fill((lep[0].momentum() + lep[1].momentum()).pT() / GeV);
  _h["pTlly_ext"]->fill(lly_system.pT() / GeV);

  _h["cent_ext"]->fill(Centrality);
  _h["dRap_ext"]->fill(Dyjj);
  _h["mjj_ext"]->fill(mjj);
  _h["dPhi_ext"]->fill(fabs(deltaPhi(lly_system, jj_system)));

  // deal with EWK SR500
  if (mjj < 450 * GeV) vetoEvent; // special since mjj in SR includes the underflow

  _h["mjj"]->fill(mjj);

  if (mjj < 500 * GeV) vetoEvent;

  _h["pTjet1"]->fill(jetsMix[0].pT() / GeV);
  _h["pTy"]->fill(selectedPh[0].pT() / GeV);
  _h["pTlep1"]->fill(lep[0].pT() / GeV);
  _h["pTlly"]->fill(lly_system.pT() / GeV);
  _h["dRap"]->fill(Dyjj);
  _h["dPhi"]->fill(fabs(deltaPhi(lly_system, jj_system)));
}

/// Normalise histograms etc., after the run
void finalize() {
  scale(_h, crossSection() / femtobarn / sumOfWeights());
}

private:

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

};

RIVET_DECLARE_PLUGIN(ATLAS_2023_I2663725);

} ```