Rivet analyses

title: ATLAS_2016_I1444991

Higgs-to-WW differential cross sections at 8 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1444991

Status: VALIDATED

Authors: - Kathrin Becker

References: - Expt page: ATLAS-HIGG-2015-04 - JHEP 1608 (2016) 104 - DOI: 10.1007/JHEP08(2016)104 - arXiv: 1604.02997

Beams: p+ p+

Beam energies: (4000.0, 4000.0)GeV

Run details: - gg -> H -> W W* -> enu munu production at 8 TeV

This paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the $H\rightarrow W W^\ast \rightarrow e\nu\mu\nu$ channel, using 20.3 fb$^{-1}$ of proton-proton collision data. The data were produced at a centre-of-mass energy of $\sqrt{s} = 8$ TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012. Cross sections are measured from the observed $H\rightarrow W W^\ast \rightarrow e\nu\mu\nu$ signal yield in categories distinguished by the number of associated jets. The total cross section is measured in a fiducial region defined by the kinematic properties of the charged leptons and neutrinos. Differential cross sections are reported as a function of the number of jets, the Higgs boson transverse momentum, the dilepton rapidity, and the transverse momentum of the leading jet. The jet-veto efficiency, or fraction of events with no jets above a given transverse momentum threshold, is also reported. All measurements are compared to QCD predictions from Monte Carlo generators and fixed-order calculations, and are in agreement with the Standard Model predictions.

Source code:ATLAS_2016_I1444991.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 {

/// Higgs-to-WW differential cross sections at 8 TeV class ATLAS_2016_I1444991 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2016_I1444991);


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

  // All particles within |eta| < 5.0
  const FinalState FS(Cuts::abseta < 5.0);

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

  // Project dressed electrons with pT > 15 GeV and |eta| < 2.47
  IdentifiedFinalState el_id(FS);
  el_id.acceptIdPair(PID::ELECTRON);
  PromptFinalState el_bare(el_id);
  Cut cuts = (Cuts::abseta < 2.47) && ((Cuts::abseta <= 1.37) || (Cuts::abseta >= 1.52))
      && (Cuts::pT > 15 * 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
  IdentifiedFinalState mu_id(FS);
  mu_id.acceptIdPair(PID::MUON);
  PromptFinalState mu_bare(mu_id);
  LeptonFinder mu_dressed_FS(mu_bare, photon_id, 0.1, Cuts::abseta < 2.5 && Cuts::pT > 15 * GeV);
  declare(mu_dressed_FS, "MU_DRESSED_FS");

  // get MET from generic invisibles
  VetoedFinalState inv_fs(FS);
  inv_fs.addVetoOnThisFinalState(VisibleFinalState(FS));
  declare(inv_fs, "InvisibleFS");

  // Project jets
  FastJets jets(FS, JetAlg::ANTIKT, 0.4);
  jets.useInvisibles(JetInvisibles::NONE);
  jets.useMuons(JetMuons::NONE);
  declare(jets, "jets");

  // Book histograms
  book(_h_Njets, 2, 1, 1);
  book(_h_PtllMET, 3, 1, 1);
  book(_h_Yll, 4, 1, 1);
  book(_h_PtLead, 5, 1, 1);
  book(_h_Njets_norm, 6, 1, 1);
  book(_h_PtllMET_norm, 7, 1, 1);
  book(_h_Yll_norm, 8, 1, 1);
  book(_h_PtLead_norm, 9, 1, 1);
  book(_h_JetVeto, 10, 1, 1);

  //histos for jetveto
  std::vector<double> ptlead25_bins = {0., 25., 300.};
  std::vector<double> ptlead40_bins = {0., 40., 300.};
  book(_h_pTj1_sel25, "pTj1_sel25", ptlead25_bins);
  book(_h_pTj1_sel40, "pTj1_sel40", ptlead40_bins);
}


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

  // Get final state particles
  const FinalState& ifs = apply<FinalState>(event, "InvisibleFS");
  const DressedLeptons& good_mu = apply<LeptonFinder>(event, "MU_DRESSED_FS").dressedLeptons();
  const DressedLeptons& el_dressed = apply<LeptonFinder>(event, "EL_DRESSED_FS").dressedLeptons();
  const Jets& jets = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 25 * GeV && Cuts::abseta < 4.5);

  //find good electrons
  DressedLeptons good_el;
  for (const DressedLepton& el : el_dressed) {
    bool keep = true;
    for (const DressedLepton& mu : good_mu) {
      keep &= deltaR(el, mu) >= 0.1;
    }
    if (keep) good_el += el;
  }

  // select only emu events
  if ((good_el.size() != 1) || good_mu.size() != 1) vetoEvent;

  //built dilepton
  FourMomentum dilep = good_el[0].momentum() + good_mu[0].momentum();
  double Mll = dilep.mass();
  double Yll = dilep.rapidity();
  double DPhill = fabs(deltaPhi(good_el[0], good_mu[0]));
  double pTl1 = (good_el[0].pT() > good_mu[0].pT()) ? good_el[0].pT() : good_mu[0].pT();

  //get MET
  FourMomentum met;
  for (const Particle& p : ifs.particles()) met += p.momentum();

  // do a few cuts before looking at jets
  if (pTl1 <= 22. || DPhill >= 1.8 || met.pT() <= 20.) vetoEvent;
  if (Mll <= 10. || Mll >= 55.) vetoEvent;

  Jets jets_selected;
  for (const Jet& j : jets) {
    if (j.abseta() > 2.4 && j.pT() <= 30 * GeV) continue;
    bool keep = true;
    for (DressedLepton el : good_el) {
      keep &= deltaR(j, el) >= 0.3;
    }
    if (keep) jets_selected += j;
  }

  double PtllMET = (met + good_el[0].momentum() + good_mu[0].momentum()).pT();

  double Njets = jets_selected.size() > 2 ? 2 : jets_selected.size();
  double pTj1 = jets_selected.size() ? jets_selected[0].pT() : 0.1;

  // Fill histograms
  _h_Njets->fill(Njets);
  _h_PtllMET->fill(PtllMET);
  _h_Yll->fill(fabs(Yll));
  _h_PtLead->fill(pTj1);
  _h_Njets_norm->fill(Njets);
  _h_PtllMET_norm->fill(PtllMET);
  _h_Yll_norm->fill(fabs(Yll));
  _h_PtLead_norm->fill(pTj1);
  _h_pTj1_sel25->fill(pTj1);
  _h_pTj1_sel40->fill(pTj1);
}


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

  const double xs = crossSectionPerEvent() / femtobarn;

  /// @todo Normalise, scale and otherwise manipulate histograms here
  scale(_h_Njets, xs);
  scale(_h_PtllMET, xs);
  scale(_h_Yll, xs);
  scale(_h_PtLead, xs);
  normalize(_h_Njets_norm);
  normalize(_h_PtllMET_norm);
  normalize(_h_Yll_norm);
  normalize(_h_PtLead_norm);
  scale(_h_pTj1_sel25, xs);
  scale(_h_pTj1_sel40, xs);
  normalize(_h_pTj1_sel25);
  normalize(_h_pTj1_sel40);
  // fill jet veto efficiency histogram
  _h_JetVeto->bin(1).set(_h_pTj1_sel25->bin(1).sumW(), _h_pTj1_sel25->bin(1).errW());
  _h_JetVeto->bin(2).set(_h_PtLead_norm->bin(1).sumW(), _h_PtLead_norm->bin(1).errW());
  _h_JetVeto->bin(3).set(_h_pTj1_sel40->bin(1).sumW(), _h_pTj1_sel25->bin(1).errW());

  scale(_h_PtLead_norm, 1000.);  // curveball unit change in HepData, just for this one
  scale(_h_PtllMET_norm, 1000.); // curveball unit change in HepData, and this one
}

private:

/// @name Histograms
/// @{
Histo1DPtr _h_Njets;
Histo1DPtr _h_PtllMET;
Histo1DPtr _h_Yll;
Histo1DPtr _h_PtLead;
Histo1DPtr _h_Njets_norm;
Histo1DPtr _h_PtllMET_norm;
Histo1DPtr _h_Yll_norm;
Histo1DPtr _h_PtLead_norm;

Estimate1DPtr _h_JetVeto;

Histo1DPtr _h_pTj1_sel25;
Histo1DPtr _h_pTj1_sel40;

};

RIVET_DECLARE_PLUGIN(ATLAS_2016_I1444991);

} ```