Rivet analyses

title: CMS_2020_I1814328

W$^+$W$^-$ boson pair production in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Experiment: CMS (LHC)

Inspire ID: 1814328

Status: VALIDATED

Authors: - cms-pag-conveners-smp@cern.ch - Guillelmo Gomez-Ceballos

References: - arXiv: 2009.00119 - Expt page: CMS-SMP-18-004 - Phys. Rev. D 102 (2020) 092001

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - pp to W+W- interactions at $\sqrt{s} = 13$ TeV. Data collected by CMS during the year 2016.

A measurement of the W W boson pair production cross section in proton-proton collisions at sqrt(s) = 13 TeV is presented. The data used in this study were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 35.9 fb-1. The W+W- candidate events are selected by first requiring two oppositely-charged leptons (electrons or muons). Two methods for reducing background contributions are employed. In the first one, a sequence of requirements on kinematic quantities is applied allowing a measurement of the total cross section: 117.6 +/- 6.8 pb which agrees well with the theoretical cross section. Fiducial cross sections are also reported for events with zero jets or one jet, and the change in the zero-jet fiducial cross section with the jet pT threshold is measured. Normalized differential cross sections are reported within the fiducial region; these are compared to theoretical predictions based on quantum chromodynamics at next-to-next-to-leading-order accuracy. A second method for suppressing background contributions employs two random forest classifiers. The analysis based on this method includes a measurement of the total cross section and also a measurement of the normalized jet multiplicity distribution in W+W- events. Finally, a dilepton invariant mass distribution is used to probe for physics beyond the standard model in the context of an effective field theory and limits on the presence of dimension-6 operators are derived.

Source code:CMS_2020_I1814328.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"

namespace Rivet {

/// @brief Measurements of W+W- boson pair production in pp collisions at 13 TeV class CMS_2020_I1814328 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2020_I1814328);


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

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

  // Initialise and register projections

  // The basic final-state projection:
  // all final-state particles within
  // the given eta acceptance
  const FinalState fs(Cuts::abseta < 4.9);
  const FinalState fsjet4p5(Cuts::abseta < 4.5);
  const FinalState fsjet2p5(Cuts::abseta < 2.5);

  // The final-state particles declared above are clustered using FastJet with
  // the anti-kT algorithm and a jet-radius parameter 0.4
  // muons and neutrinos are excluded from the clustering
  FastJets jet4p5fs(fsjet4p5, JetAlg::ANTIKT, 0.4);
  declare(jet4p5fs, "jets4p5");
  FastJets jet2p5fs(fsjet2p5, JetAlg::ANTIKT, 0.4);
  declare(jet2p5fs, "jets2p5");

  // FinalState of prompt photons and bare muons and electrons in the event
  PromptFinalState photons(Cuts::abspid == PID::PHOTON);
  PromptFinalState bare_leps(Cuts::abspid == PID::MUON || Cuts::abspid == PID::ELECTRON);
  bare_leps.acceptTauDecays(false);

  // Dress the prompt bare leptons with prompt photons within dR < 0.1,
  // and apply some fiducial cuts on the dressed leptons
  Cut lepton_cuts = Cuts::abseta < 2.5 && Cuts::pT > 25 * GeV;
  LeptonFinder dressed_leps(bare_leps, photons, 0.1, lepton_cuts);
  declare(dressed_leps, "leptons");

  // Missing momentum
  declare(MissingMomentum(fs), "MET");

  // Book histograms
  book(_h_WW_njets_norm, 2, 1, 1);
  book(_h["mll"], 4, 1, 1);
  book(_h["ptlmax"], 5, 1, 1);
  book(_h["ptlmin"], 6, 1, 1);
  book(_h["dphill"], 7, 1, 1);
  book(_h_WW_njet0, 8, 1, 1);
}

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

  if (_edges.empty()) {
    _edges = _h_WW_njets_norm->xEdges();
    _edges0 = _h_WW_njet0->xEdges();
  }

  // Apply a missing-momentum cut
  if (apply<MissingMomentum>(event, "MET").missingPt() < 20 * GeV) return;

  // Retrieve dressed leptons, sorted by pT
  DressedLeptons leptons = apply<LeptonFinder>(event, "leptons").dressedLeptons();

  // Retrieve clustered jets, sorted by pT, with a minimum pT cut
  Jets jets25 = apply<FastJets>(event, "jets4p5").jetsByPt(Cuts::pT > 25 * GeV);
  Jets jets30 = apply<FastJets>(event, "jets4p5").jetsByPt(Cuts::pT > 30 * GeV);
  Jets jets35 = apply<FastJets>(event, "jets4p5").jetsByPt(Cuts::pT > 35 * GeV);
  Jets jets45 = apply<FastJets>(event, "jets4p5").jetsByPt(Cuts::pT > 45 * GeV);
  Jets jets60 = apply<FastJets>(event, "jets4p5").jetsByPt(Cuts::pT > 60 * GeV);
  Jets jetsNj = apply<FastJets>(event, "jets2p5").jetsByPt(Cuts::pT > 30 * GeV);

  // Remove all jets within dR < 0.4 of a dressed lepton
  idiscardIfAnyDeltaRLess(jets25, leptons, 0.4);
  idiscardIfAnyDeltaRLess(jets30, leptons, 0.4);
  idiscardIfAnyDeltaRLess(jets35, leptons, 0.4);
  idiscardIfAnyDeltaRLess(jets45, leptons, 0.4);
  idiscardIfAnyDeltaRLess(jets60, leptons, 0.4);
  idiscardIfAnyDeltaRLess(jetsNj, leptons, 0.4);

  if (leptons.size() == 2 && leptons[0].pid() * leptons[1].pid() < 0) {
    FourMomentum dilCand = leptons[0].momentum() + leptons[1].momentum();
    if (dilCand.mass() > 20 * GeV && dilCand.pT() > 30 * GeV) {
      double ptlmax = leptons[0].pT();
      double ptlmin = leptons[1].pT();
      if (ptlmax < ptlmin) {
        ptlmax = leptons[1].pT();
        ptlmin = leptons[0].pT();
      }

      if (leptons[0].abspid() != leptons[1].abspid()) {
        _h_WW_njets_norm->fill(_edges[min((int)jetsNj.size(), 2)]);
        _h["mll"]->fill(min(dilCand.mass() / GeV, 1499.999));
        _h["ptlmax"]->fill(min(ptlmax / GeV, 399.999));
        _h["ptlmin"]->fill(min(ptlmin / GeV, 149.999));
        _h["dphill"]->fill(deltaPhi(leptons[0], leptons[1]));
      }

      if (jets25.size() == 0) _h_WW_njet0->fill(_edges0[0]);
      if (jets30.size() == 0) _h_WW_njet0->fill(_edges0[1]);
      if (jets35.size() == 0) _h_WW_njet0->fill(_edges0[2]);
      if (jets45.size() == 0) _h_WW_njet0->fill(_edges0[3]);
      if (jets60.size() == 0) _h_WW_njet0->fill(_edges0[4]);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {

  double norm = (sumOfWeights() != 0) ? crossSection() / picobarn / sumOfWeights() : 1.0;

  normalize(_h_WW_njets_norm);
  for (auto& item : _h) {
    const double rho = item.second->densitySum();
    if (rho) scale(item.second, 1.0 / rho);
  }
  scale(_h_WW_njet0, norm);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_WW_njets_norm, _h_WW_njet0;
map<string, Histo1DPtr> _h;
vector<string> _edges, _edges0;
/// @}

};

RIVET_DECLARE_PLUGIN(CMS_2020_I1814328);

} ```