Rivet analyses

title: ATLAS_2019_I1734263

WW production at 13 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1734263

Status: VALIDATED

Authors: - Kristin Lohwasser - Christian Gutschow - Hannes Mildner

References: - Expt page: ATLAS-STDM-2017-24 - arXiv: 1905.04242

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - pp -> WW production at 13 TeV

A measurement of fiducial and differential cross-sections for $W^+W^-$ production in proton--proton collisions at $\sqrt{s}=$13~TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of $36.1$~fb$^{-1}$ is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as $WW\rightarrow e^{\pm}\nu\mu^{\mp}\nu$. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35~GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.

Source code:ATLAS_2019_I1734263.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/MissingMomentum.hh"

include "Rivet/Projections/PromptFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {

/// @brief WW production at 13 TeV class ATLAS_2019_I1734263 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1734263);


/// @name Analysis methods
/// @{

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

  const FinalState fs(Cuts::abseta < 5.);

  // Project photons for dressing
  FinalState photon_id(Cuts::abspid == PID::PHOTON);

  // Cuts for leptons
  Cut lepton_cuts = (Cuts::abseta < 2.5) && (Cuts::pT > 27 * GeV);
  // Lepton for simplified phase space (e.g. for comparison with CMS)
  Cut lepton_cuts_simpl = (Cuts::abseta < 2.5) && (Cuts::pT > 25 * GeV);

  // Project dressed leptons (e/mu not from tau) with pT > 27 GeV and |eta| < 2.5
  // Both for normal and simplified phase space
  PromptFinalState lep_bare(Cuts::abspid == PID::MUON || Cuts::abspid == PID::ELECTRON);
  LeptonFinder lep_dressed(lep_bare, photon_id, 0.1, lepton_cuts);
  declare(lep_dressed, "lep_dressed");
  LeptonFinder lep_dressed_simpl(lep_bare, photon_id, 0.1, lepton_cuts_simpl);
  declare(lep_dressed_simpl, "lep_dressed_simpl");

  // Get MET
  MissingMomentum mm(fs);
  declare(mm, "met");

  // Define hadrons as everything but dressed leptons (for jet clustering)
  VetoedFinalState hadrons(fs);
  hadrons.addVetoOnThisFinalState(lep_dressed);
  declare(hadrons, "hadrons");
  VetoedFinalState hadrons_simpl(fs);
  hadrons_simpl.addVetoOnThisFinalState(lep_dressed_simpl);
  declare(hadrons_simpl, "hadrons_simpl");

  // Project jets
  FastJets jets(hadrons, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::NONE);
  declare(jets, "jets");
  FastJets jets_simpl(hadrons_simpl, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::NONE);
  declare(jets_simpl, "jets_simpl");


  // Book histograms
  // fiducial differential cross section as a function of the jet-veto pt cut
  book(_d, 1, 1, 1);

  // fiducial differential cross section (leading lepton pt)
  book(_h["ptlead"], 4, 1, 1);
  book(_h["ptlead_norm"], 22, 1, 1);
  book(_h["ptlead_simpl"], 41, 1, 1);

  // fiducial differential cross section (dilepton-system mll)
  book(_h["mll"], 7, 1, 1);
  book(_h["mll_norm"], 25, 1, 1);
  book(_h["mll_simpl"], 42, 1, 1);

  // fiducial differential cross section (dilepton-system ptll)
  book(_h["ptll"], 10, 1, 1);
  book(_h["ptll_norm"], 28, 1, 1);
  book(_h["ptll_simpl"], 43, 1, 1);

  // fiducial differential cross section (absolute rapidity of dilepton-system y_ll)
  book(_h["yll"], 13, 1, 1);
  book(_h["yll_norm"], 31, 1, 1);

  // fiducial differential cross section (dilepton-system delta_phi_ll)
  book(_h["dphill"], 16, 1, 1);
  book(_h["dphill_norm"], 34, 1, 1);


  // fiducial differential cross section (absolute costheta* of dilepton-system costhetastar_ll)
  book(_h["costhetastarll"], 19, 1, 1);
  book(_h["costhetastarll_norm"], 37, 1, 1);
}


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

  // Get met and find leptons
  const MissingMomentum& met = apply<MissingMomentum>(event, "met");
  const DressedLeptons& leptons = apply<LeptonFinder>(event, "lep_dressed").dressedLeptons();
  const DressedLeptons& leptons_simpl = apply<LeptonFinder>(event, "lep_dressed_simpl").dressedLeptons();

  // Find jets and jets for simplified phase space (for the latter slightly different leptons are excluded from clustering)
  const Jets& jets30 = apply<FastJets>(event, "jets").jetsByPt(Cuts::abseta < 4.5 && Cuts::pT > 30 * GeV);
  const Jets& jets_simpl = apply<FastJets>(event, "jets_simpl")
                               .jetsByPt(Cuts::abseta < 4.5 && Cuts::pT > 30 * GeV);

  // Define observables
  const FourMomentum dilep = leptons.size() > 1 ? leptons[0].momentum() + leptons[1].momentum()
                                                : FourMomentum(0, 0, 0, 0);
  const double ptll = leptons.size() > 1 ? dilep.pT() / GeV : -1;
  const double Mll = leptons.size() > 1 ? dilep.mass() / GeV : -1;
  const double Yll = leptons.size() > 1 ? dilep.absrap() : -5;
  const double DPhill = leptons.size() > 1 ? fabs(deltaPhi(leptons[0], leptons[1])) : -1.;
  const double costhetastar = leptons.size() > 1 ? fabs(tanh((leptons[0].eta() - leptons[1].eta()) / 2))
                                                 : -0.2;

  // Define observables for simplified PS
  const FourMomentum dilep_simpl = leptons_simpl.size() > 1
      ? leptons_simpl[0].momentum() + leptons_simpl[1].momentum()
      : FourMomentum(0, 0, 0, 0);
  const double ptll_simpl = leptons_simpl.size() > 1 ? dilep_simpl.pT() / GeV : -1;
  const double Mll_simpl = leptons_simpl.size() > 1 ? dilep_simpl.mass() / GeV : -1;

  // Cuts for simplified PS
  bool veto_simpl = false;
  // Remove events that do not contain 2 good leptons (either muons or electrons)
  if (leptons_simpl.size() != 2) veto_simpl = true;
  // Veto same-flavour events
  else if (leptons_simpl[0].abspid() == leptons_simpl[1].abspid())
    veto_simpl = true;
  // Veto same-charge events
  else if (leptons_simpl[0].pid() * leptons_simpl[1].pid() > 0)
    veto_simpl = true;
  // MET (pt-MET) cut
  else if (met.missingPt() <= 20 * GeV)
    veto_simpl = true;
  // jetveto
  else if (!jets_simpl.empty())
    veto_simpl = true;

  // Fill histos for simplified phase space
  if (!veto_simpl) {
    _h["ptlead_simpl"]->fill(leptons_simpl[0].pT() / GeV);
    _h["ptll_simpl"]->fill(ptll_simpl);
    _h["mll_simpl"]->fill(Mll_simpl);
  }


  // Event selection for proper fiducial phase space
  // Remove events that do not contain 2 good leptons (either muons or electrons)
  if (leptons.size() != 2) vetoEvent;
  // Veto same-flavour events
  if (leptons[0].abspid() == leptons[1].abspid()) vetoEvent;
  // Veto same-charge events
  if (leptons[0].pid() * leptons[1].pid() > 0) vetoEvent;
  // MET (pt-MET) cut
  if (met.missingPt() <= 20 * GeV) vetoEvent;
  // m_ll cut
  if (dilep.mass() <= 55 * GeV) vetoEvent;
  // pt_ll cut
  if (dilep.pT() <= 30 * GeV) vetoEvent;

  // Fill cross section as function of veto-jet pt before applying jet veto
  if (jets30.empty() || jets30[0].pT() / GeV < 30.) _d->fill(30);
  if (jets30.empty() || jets30[0].pT() / GeV < 35.) _d->fill(35);
  if (jets30.empty() || jets30[0].pT() / GeV < 40.) _d->fill(40);
  if (jets30.empty() || jets30[0].pT() / GeV < 45.) _d->fill(45);
  if (jets30.empty() || jets30[0].pT() / GeV < 50.) _d->fill(50);
  if (jets30.empty() || jets30[0].pT() / GeV < 55.) _d->fill(55);
  if (jets30.empty() || jets30[0].pT() / GeV < 60.) _d->fill(60);
  // Jet veto at 35 GeV is the default
  if (!jets30.empty() && jets30[0].pT() / GeV > 35.) vetoEvent;

  // fill histograms
  _h["ptlead"]->fill(leptons[0].pT() / GeV);
  _h["ptlead_norm"]->fill(leptons[0].pT() / GeV);

  _h["ptll"]->fill(ptll);
  _h["ptll_norm"]->fill(ptll);

  _h["mll"]->fill(Mll);
  _h["mll_norm"]->fill(Mll);

  _h["yll"]->fill(Yll);
  _h["yll_norm"]->fill(Yll);

  _h["dphill"]->fill(DPhill);
  _h["dphill_norm"]->fill(DPhill);

  _h["costhetastarll"]->fill(costhetastar);
  _h["costhetastarll_norm"]->fill(costhetastar);
}


/// Normalise histograms etc., after the run
void finalize() {
  const double sf(crossSection() / femtobarn / sumOfWeights());
  // scale histogram by binwidth, as bin content is actually a integrated fiducial cross section
  // scale to cross section
  scale(_d, sf);
  for (auto& hist : _h) {
    scale(hist.second, sf);
    if (hist.first.find("norm") != string::npos) normalize(hist.second);
  }
}

/// @}

private:

/// @name Histograms
/// @{
map<string, Histo1DPtr> _h;
BinnedHistoPtr<int> _d;
/// @}

};

RIVET_DECLARE_PLUGIN(ATLAS_2019_I1734263);

} ```