Rivet analyses

title: ATLAS_2019_I1738841

Same-sign $WW$ Observation at 13 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1738841

Status: VALIDATED

Authors: - Stefanie Todt - Philip Sommer - Rustem Ospanov

References: - Expt page: ATLAS-STDM-2017-06 - arXiv: 1906.03203 - Phys. Rev. Lett. 123 (2019) 161801 - DOI: 10.1103/PhysRevLett.123.161801

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - $p p \to \ell \nu \ell \nu j j$ at 13 TeV

This Letter presents the observation and measurement of electroweak production of a same-sign $W$ boson pair in association with two jets using 36.1 fb$^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of $\sqrt{s}=13$ TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector fiducial phase-space region, defined by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference. A total of 122 candidate events are observed for a background expectation of $69 \pm 7$ events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial signal cross section is $\sigma^{\textrm {fid.}}=2.89^{+0.51}{-0.48}~\textrm{(stat.)}\ ^{+0.29}{-0.28}~\textrm{(syst.)}\textrm{ fb}$.

Source code:ATLAS_2019_I1738841.cc

```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 same-sign WW at 13 TeV class ATLAS_2019_I1738841 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1738841);


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

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

  FinalState allLeps(Cuts::abspid == PID::ELECTRON || Cuts::abspid == PID::MUON);
  PromptFinalState promptLeps(allLeps);
  FinalState photons(Cuts::abspid == PID::PHOTON);

  Cut dressedLep_cuts = (Cuts::abseta < 2.5) && (Cuts::pT > 27 * GeV);
  LeptonFinder dressedLeps(promptLeps, photons, 0.1, dressedLep_cuts);
  declare(dressedLeps, "dressedLeptons");

  // veto on leptons from prompt tau decays
  VetoedFinalState lepsFromTaus(PromptFinalState(allLeps, TauDecaysAs::PROMPT));
  lepsFromTaus.addVetoOnThisFinalState(promptLeps);
  LeptonFinder vetoLeps(lepsFromTaus, photons, 0.1, dressedLep_cuts);
  declare(vetoLeps, "vetoLeptons");

  declare(MissingMomentum(), "eTmiss");

  VetoedFinalState vfs(FinalState(Cuts::abseta < 4.5));
  vfs.addVetoOnThisFinalState(dressedLeps);
  FastJets jets(vfs, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::NONE);
  declare(jets, "jets");

  // Histograms
  book(_c, 1, 1, 1);
}


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

  if (apply<LeptonFinder>(event, "vetoLeptons").dressedLeptons().size()) vetoEvent;

  const DressedLeptons& dressedLeptons = apply<LeptonFinder>(event, "dressedLeptons").dressedLeptons();
  if (dressedLeptons.size() != 2) vetoEvent;
  const Particle& lep1 = dressedLeptons[0];
  const Particle& lep2 = dressedLeptons[1];

  const Jets& jets = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 35 * GeV);
  if (jets.size() < 2) vetoEvent;

  // pT of the two leading jets
  const Jet& tagJet1 = jets[0];
  const Jet& tagJet2 = jets[1];
  if (tagJet1.pT() < 65.) vetoEvent;
  if (tagJet2.pT() < 35.) vetoEvent;

  // leptons isolation from jets (dR >= 0.3)
  float f_lj_dRmin = 999;
  for (const Jet& j : jets) {
    float dR = deltaR(j, lep1);
    if (dR < f_lj_dRmin) f_lj_dRmin = dR;
    dR = deltaR(j, lep2);
    if (dR < f_lj_dRmin) f_lj_dRmin = dR;
  }
  if (f_lj_dRmin < 0.3) vetoEvent;

  // same sign leptons
  if (lep1.pid() * lep2.pid() < 0) vetoEvent;

  // lepton isolation
  const float f_ll_dR = deltaR(lep1.momentum(), lep2.momentum());
  if (f_ll_dR < 0.3) vetoEvent;

  // m_ll > 20 GeV
  const float f_ll_m = (lep1.momentum() + lep2.momentum()).mass() / GeV;
  if (f_ll_m < 20.) vetoEvent;

  // MET > 30 GeV
  const double ETmiss = apply<MissingMomentum>(event, "eTmiss").missingPt() / GeV;
  if (ETmiss < 30.) vetoEvent;

  // m_jj >= 500 GeV
  const float f_tjets_m = (tagJet1.momentum() + tagJet2.momentum()).mass() / GeV;
  if (f_tjets_m < 500.) vetoEvent;

  // dY_jj >= 2
  const float f_tjets_dY = deltaRap(tagJet1, tagJet2);
  if (f_tjets_dY < 2) vetoEvent;

  // --- fill histograms ---
  _c->fill();
}


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

/// @}


/// @name Histograms
/// @{
CounterPtr _c;
/// @}

};

RIVET_DECLARE_PLUGIN(ATLAS_2019_I1738841); } ```