Rivet analyses

title: ATLAS_2016_I1426515

WW production at 8 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1426515

Status: VALIDATED

Authors: - Kristin Lohwasser - Christian Gutschow

References: - Expt page: ATLAS-STDM-2013-07 - JHEP 1609 (2016) 029 - DOI: 10.1007/JHEP09(2016)029 - arXiv: 1603.01702

Beams: p+ p+

Beam energies: (4000.0, 4000.0)GeV

Run details: - pp -> WW production at 8 TeV

The production of $W$ boson pairs in proton--proton collisions at $\sqrt{s} = 8$ TeV is studied using data corresponding to 20.3 fb${}^{-1}$ of integrated luminosity collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The $W$ bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with reconstructed jets are not included in the candidate event sample. A total of 6636 $WW$ candidate events are observed. Measurements are performed in fiducial regions closely approximating the detector acceptance. The integrated measurement is corrected for all acceptance effects and for the $W$ branching fractions to leptons in order to obtain the total $WW$ production cross section, which is found to be $71.1 \pm 1.1$ (stat) ${}^{+5.7}{-5.0}$ (syst) $\pm 1.4$ (lumi) pb. This agrees with the next-to-next-to-leading-order Standard Model prediction of $63.2 {}^{+1.6}{-1.4}$ (scale) $\pm 1.2$ (PDF) pb. Fiducial differential cross sections are measured as a function of each of six kinematic variables. The distribution of the transverse momentum of the leading lepton is used to set limits on anomalous triple-gauge-boson couplings.

Source code:ATLAS_2016_I1426515.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/PromptFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

include "Rivet/Projections/VisibleFinalState.hh"

namespace Rivet {

/// WW production at 8 TeV class ATLAS_2016_I1426515 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2016_I1426515);


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

  const FinalState fs(Cuts::abseta < 4.5);

  // Project photons for dressing
  IdentifiedFinalState photon_id(fs);
  photon_id.acceptIdPair(PID::PHOTON);

  // Project dressed electrons with pT > 15 GeV and |eta| < 2.47
  PromptFinalState el_bare(FinalState(Cuts::abspid == PID::ELECTRON));
  Cut cuts = (Cuts::abseta < 2.47) && ((Cuts::abseta <= 1.37) || (Cuts::abseta >= 1.52))
      && (Cuts::pT > 10 * GeV);
  LeptonFinder el_dressed_FS(el_bare, photon_id, 0.1, cuts);
  declare(el_dressed_FS, "EL_DRESSED_FS");

  // Project dressed muons with pT > 15 GeV and |eta| < 2.5
  PromptFinalState mu_bare(FinalState(Cuts::abspid == PID::MUON));
  LeptonFinder mu_dressed_FS(mu_bare, photon_id, 0.1, Cuts::abseta < 2.4 && Cuts::pT > 15 * GeV);
  declare(mu_dressed_FS, "MU_DRESSED_FS");

  Cut cuts_WW = (Cuts::abseta < 2.5) && (Cuts::pT > 20 * GeV);
  IdentifiedFinalState lep_id(fs);
  lep_id.acceptIdPair(PID::MUON);
  lep_id.acceptIdPair(PID::ELECTRON);
  PromptFinalState lep_bare(lep_id);
  LeptonFinder leptons(lep_bare, photon_id, 0.1, cuts_WW);
  declare(leptons, "leptons");

  declare(FinalState(Cuts::abspid == PID::TAU || Cuts::abspid == PID::NU_TAU), "tau_id");

  // Get MET from generic invisibles
  VetoedFinalState ivfs(fs);
  ivfs.addVetoOnThisFinalState(VisibleFinalState(fs));
  declare(ivfs, "InvisibleFS");

  // Project jets
  FastJets jets(fs, JetAlg::ANTIKT, 0.4, JetMuons::NONE, JetInvisibles::NONE);
  declare(jets, "jets");


  // Integrated cross sections
  // d01 ee/mm fiducial integrated cross sections
  book(_hist_mm_fid_intxsec, 1, 1, 1);
  book(_hist_ee_fid_intxsec, 1, 1, 2);

  // d02 emme fiducial integrated cross sections
  book(_hist_emme_fid_intxsec, 2, 1, 1);

  // d10  emme fiducial differential cross section (leading lepton ptlead + ptlead normalized)
  book(_hist_emme_fid_ptlead, 10, 1, 1);
  book(_hist_emme_fid_ptleadnorm, 10, 1, 2);

  // d11  emme fiducial differential cross section (dilepton-system ptll + ptll normalized)
  book(_hist_emme_fid_ptll, 11, 1, 1);
  book(_hist_emme_fid_ptllnorm, 11, 1, 2);

  // d12  emme fiducial differential cross section (dilepton-system mll + mll normalized)
  book(_hist_emme_fid_mll, 12, 1, 1);
  book(_hist_emme_fid_mllnorm, 12, 1, 2);

  // d13  emme fiducial differential cross section (dilepton-system delta_phi_ll + dphill normalized)
  book(_hist_emme_fid_dphill, 13, 1, 1);
  book(_hist_emme_fid_dphillnorm, 13, 1, 2);

  // d14  emme fiducial differential cross section (absolute rapidity of dilepton-system y_ll + y_ll normalized)
  book(_hist_emme_fid_yll, 14, 1, 1);
  book(_hist_emme_fid_yllnorm, 14, 1, 2);

  // d15  emme fiducial differential cross section (absolute costheta* of dilepton-system costhetastar_ll + costhetastar_ll normalized)
  book(_hist_emme_fid_costhetastarll, 15, 1, 1);
  book(_hist_emme_fid_costhetastarllnorm, 15, 1, 2);
}


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

  // Find leptons
  const FinalState& ifs = apply<VetoedFinalState>(event, "InvisibleFS");
  const DressedLeptons& leptons = apply<LeptonFinder>(event, "leptons").dressedLeptons();
  const DressedLeptons& good_mu = apply<LeptonFinder>(event, "MU_DRESSED_FS").dressedLeptons();
  const DressedLeptons& good_el = apply<LeptonFinder>(event, "EL_DRESSED_FS").dressedLeptons();
  const Jets& jets = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 25 * GeV && Cuts::abseta < 4.5);

  // Taus are excluded from the fiducial cross section
  const Particles taus = apply<FinalState>(event, "tau_id")
                             .particlesByPt(Cuts::pT > 12. * GeV && Cuts::abseta < 3.0);
  if (!taus.empty()) vetoEvent;

  // Remove events that do not contain 2 good leptons (either muons or electrons)
  if (leptons.size() != 2 && (good_el.size() != 1 || good_mu.size() != 1)) vetoEvent;

  // Split into channels
  int channel = -1; // 1=mm, 2=ee;  3=emu; 4=mue
  if (good_mu.size() == 2)
    channel = 1; //mm
  else if (good_el.size() == 2)
    channel = 2; //ee
  else if (good_mu.size() == 1 && good_el.size() == 1 && good_el[0].pT() > good_mu[0].pT())
    channel = 3; //emu
  else if (good_mu.size() == 1 && good_el.size() == 1 && good_el[0].pT() < good_mu[0].pT())
    channel = 4; //mue
  if (channel == -1) vetoEvent;

  // Assign leptons
  const DressedLepton *lep1, *lep2;
  if (channel == 1) { //mm
    if (good_mu[0].pT() > good_mu[1].pT()) {
      lep1 = &good_mu[0];
      lep2 = &good_mu[1];
    }
    else {
      lep1 = &good_mu[1];
      lep2 = &good_mu[0];
    }
  }
  else if (channel == 2) { //ee
    if (good_el[0].pT() > good_el[1].pT()) {
      lep1 = &good_el[0];
      lep2 = &good_el[1];
    }
    else {
      lep1 = &good_el[1];
      lep2 = &good_el[0];
    }
  }
  else if (channel == 3) { //emu
    lep1 = &good_el[0];
    lep2 = &good_mu[0];
  }
  else { // if (channel == 4) { //mue
    lep1 = &good_mu[0];
    lep2 = &good_el[0];
  }

  // Cut on leptons
  if (lep1->pT() < 25 * GeV || lep2->pT() < 20 * GeV) vetoEvent;

  // Select jets isolated from electrons
  const Jets jets_selected = select(jets, [&](const Jet& j) { return all(good_el, deltaRGtr(j, 0.3)); });

  // Define variables
  const FourMomentum met = sum(ifs.particles(), FourMomentum());
  const FourMomentum dilep = lep1->momentum() + lep2->momentum();
  const double ptll = dilep.pT() / GeV;
  const double Mll = dilep.mass() / GeV;
  const double Yll = dilep.absrap();
  const double DPhill = fabs(deltaPhi(*lep1, *lep2));
  const double costhetastar = fabs(tanh((lep1->eta() - lep2->eta()) / 2));

  // Calculate dphi to MET
  double DPhi_met = fabs(deltaPhi((*lep1), met));
  if (fabs(deltaPhi((*lep2), met)) < DPhi_met) DPhi_met = fabs(deltaPhi((*lep2), met));
  if (DPhi_met > M_PI / 2)
    DPhi_met = 1.;
  else
    DPhi_met = fabs(sin(DPhi_met));

  // Apply selections
  // mll lower cut (reject quarkonia)
  if ((channel == 1 || channel == 2) && Mll < 15.)
    vetoEvent;
  else if (Mll < 10.)
    vetoEvent;

  // Z veto (reject Z -- only dilepton channels)
  if ((channel == 1 || channel == 2) && abs(Mll - 91.1876) < 15.) vetoEvent;

  // Met rel cut
  if ((channel == 1 || channel == 2) && met.pT() * DPhi_met < 45 * GeV)
    vetoEvent;
  else if (met.pT() * DPhi_met < 15 * GeV)
    vetoEvent;

  // MET (pt-MET) cut
  if ((channel == 1 || channel == 2) && met.pT() <= 45 * GeV)
    vetoEvent; // begin MET cut
  else if (met.pT() <= 20 * GeV)
    vetoEvent;

  // Require 0 jets
  if (!jets_selected.empty()) vetoEvent;

  // Fill histograms
  if (channel == 1) {
    _hist_mm_fid_intxsec->fill(1.0);
  }
  else if (channel == 2) {
    _hist_ee_fid_intxsec->fill(1.0);
  }
  else if (channel == 3 || channel == 4) {
    _hist_emme_fid_intxsec->fill(1.0);

    _hist_emme_fid_ptlead->fill(lep1->pT() / GeV);
    _hist_emme_fid_ptleadnorm->fill(lep1->pT() / GeV);

    _hist_emme_fid_ptll->fill(ptll);
    _hist_emme_fid_ptllnorm->fill(ptll);

    _hist_emme_fid_mll->fill(Mll);
    _hist_emme_fid_mllnorm->fill(Mll);

    _hist_emme_fid_dphill->fill(DPhill);
    _hist_emme_fid_dphillnorm->fill(DPhill);

    _hist_emme_fid_yll->fill(Yll);
    _hist_emme_fid_yllnorm->fill(Yll);

    _hist_emme_fid_costhetastarll->fill(costhetastar);
    _hist_emme_fid_costhetastarllnorm->fill(costhetastar);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  const double sf(crossSection() / femtobarn / sumOfWeights());
  scale(_hist_mm_fid_intxsec, sf);
  scale(_hist_ee_fid_intxsec, sf);
  scale(_hist_emme_fid_intxsec, sf);
  scale(_hist_emme_fid_ptlead, sf);
  scale(_hist_emme_fid_ptll, sf);
  scale(_hist_emme_fid_mll, sf);
  scale(_hist_emme_fid_dphill, sf);
  scale(_hist_emme_fid_yll, sf);
  scale(_hist_emme_fid_costhetastarll, sf);
  normalize(_hist_emme_fid_ptleadnorm);
  normalize(_hist_emme_fid_ptllnorm);
  normalize(_hist_emme_fid_mllnorm);
  normalize(_hist_emme_fid_dphillnorm);
  normalize(_hist_emme_fid_yllnorm);
  normalize(_hist_emme_fid_costhetastarllnorm);
}

private:

/// @name Histograms
/// @{

// d01 ee/mm fiducial integrated cross sections
Histo1DPtr _hist_mm_fid_intxsec, _hist_ee_fid_intxsec;

// d02 emme fiducial integrated cross sections
Histo1DPtr _hist_emme_fid_intxsec;

// d10  emme fiducial differential cross section (leading lepton ptlead + ptlead normalized)
Histo1DPtr _hist_emme_fid_ptlead, _hist_emme_fid_ptleadnorm;

// d11  emme fiducial differential cross section (dilepton-system ptll + ptll normalized)
Histo1DPtr _hist_emme_fid_ptll, _hist_emme_fid_ptllnorm;

// d12  emme fiducial differential cross section (dilepton-system mll + mll normalized)
Histo1DPtr _hist_emme_fid_mll, _hist_emme_fid_mllnorm;

// d13  emme fiducial differential cross section (dilepton-system delta_phi_ll + dphill normalized)
Histo1DPtr _hist_emme_fid_dphill, _hist_emme_fid_dphillnorm;

// d14  emme fiducial differential cross section (absolute rapidity of dilepton-system y_ll + y_ll normalized)
Histo1DPtr _hist_emme_fid_yll, _hist_emme_fid_yllnorm;

// d15  emme fiducial differential cross section (absolute costheta* of dilepton-system costhetastar_ll + costhetastar_ll normalized)
Histo1DPtr _hist_emme_fid_costhetastarll, _hist_emme_fid_costhetastarllnorm;
/// @}

};

RIVET_DECLARE_PLUGIN(ATLAS_2016_I1426515);

} ```