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ATLAS_2015_I1364361

Total and differential Higgs cross sections at 8 TeV with ATLAS
Experiment: ATLAS (LHC)
Inspire ID: 1364361
Status: VALIDATED
Authors:
  • Michaela Queitsch-Maitland
References: Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • pp Higgs production at 8 TeV, include all processes (ggH, VH, VBF, ttH), stable Higgs

WARNING --- this analysis requires stable higgs bosons --- Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3 fb1 of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of 8 TeV and recorded by the ATLAS detector. Cross sections are obtained from measured Higgs to diphoton and ZZ* event yields, which are combined accounting for detector efficiencies, fiducial acceptances and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be 33.0 5.3 (stat) 1.6 (sys) pb.

Source code: ATLAS_2015_I1364361.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {


  /// @brief Higgs differential cross-section combination between the ATLAS measurements in the yy and 4l channels
  ///
  /// Computes Higgs transverse momentum, rapidity, jet multiplicity and leading jet pT.
  ///
  /// @author Michaela Queitsch-Maitland <michaela.queitsch-maitland@cern.ch>
  /// @author Dag Gillberg <dag.gillberg@cern.ch>
  /// @author Florian Bernlochner <florian.bernlochner@cern.ch>
  /// @author Sarah Heim <sarah.heim@cern.ch>
  class ATLAS_2015_I1364361 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2015_I1364361);


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

      // All final state particles
      const FinalState fs;
      declare(fs, "FS");

      // Histograms with data bins
      _h_pTH_incl   = bookHisto1D(1,1,1);
      _h_yH_incl    = bookHisto1D(2,1,1);
      _h_Njets_incl = bookHisto1D(3,1,1);
      _h_pTj1_incl  = bookHisto1D(4,1,1);
    }


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

      // Get the final state particles ordered by pT
      const Particles& fs = apply<FinalState>(event, "FS").particlesByPt();

      // Find a stable Higgs (mandatory)
      const auto higgsiter = std::find_if(fs.begin(), fs.end(), [](const Particle& p){ return p.pid() == PID::HIGGSBOSON; });
      if (higgsiter == fs.end()) vetoEvent;
      const Particle& higgs = *higgsiter;

      // bool stable_higgs = false;
      // const Particle* higgs = 0;
      // for (const Particle& p : fs) {
      //   if (p.pid() == PID::HIGGSBOSON) {
      //     stable_higgs = true;
      //     higgs = &p;
      //     break;
      //   }
      // }
      // if (!stable_higgs) {
      //   MSG_WARNING("FATAL: No stable Higgs found in event record.\n");
      //   vetoEvent;
      // }


      // Loop over final state particles and fill various particle vectors
      Particles leptons, photons, jet_ptcls;
      foreach ( const Particle& ptcl, fs ) {
        // Do not include the Higgs in jet finding!
        if ( ptcl.pid() == PID::HIGGSBOSON ) continue;
        // Neutrinos not from hadronisation
        if ( ptcl.isNeutrino() && !ptcl.fromHadron() ) continue;
        // Electrons and muons not from hadronisation
        if ( ( ptcl.abspid() == PID::ELECTRON || ptcl.abspid() == PID::MUON ) && !ptcl.fromHadron() ) {
          leptons.push_back(ptcl);
          continue;
        }
        // Photons not from hadronisation
        if ( ptcl.abspid() == PID::PHOTON && !ptcl.fromHadron() ) {
          photons.push_back(ptcl);
          continue;
        }
        // Add particle to jet inputs
        jet_ptcls.push_back(ptcl);
      }

      // Match FS photons to leptons within cone R=0.1
      // If they are not 'dressing' photons, add to jet particle vector
      foreach ( const Particle& ph, photons ) {
        bool fsr_photon = false;
        foreach ( const Particle& lep, leptons ) {
          if ( deltaR(ph.momentum(),lep.momentum()) < 0.1 ){
            fsr_photon=true;
            continue;
          }
        }
        if ( !fsr_photon ) jet_ptcls.push_back(ph);
      }

      // Let's build the jets! By hand...
      const PseudoJets pjs_in = mkPseudoJets(jet_ptcls);
      const fastjet::JetDefinition jdef(fastjet::antikt_algorithm, 0.4);
      const Jets alljets = mkJets(fastjet::ClusterSequence(pjs_in, jdef).inclusive_jets());
      const Jets jets = sortByPt(filterBy(alljets, Cuts::pT > 30*GeV && Cuts::absrap < 4.4));
      // FastJets jet_pro(FastJets::ANTIKT, 0.4);
      // jet_pro.calc(jet_ptcls);
      // Jets jets = jet_pro.jetsByPt(Cuts::pT > 30*GeV && Cuts::absrap < 4.4);

      const double weight = event.weight();
      _h_pTH_incl->fill(higgs.pT(), weight);
      _h_yH_incl->fill(higgs.absrap(), weight);
      _h_Njets_incl->fill(jets.size() > 3 ? 3 : jets.size(), weight);
      _h_pTj1_incl->fill(jets.empty() ? 0 : jets[0].pT(), weight);
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double xs = crossSectionPerEvent();
      scale(_h_pTH_incl, xs);
      scale(_h_yH_incl, xs);
      scale(_h_Njets_incl, xs);
      scale(_h_pTj1_incl, xs);
    }


  private:

    Histo1DPtr _h_pTH_incl, _h_yH_incl, _h_Njets_incl, _h_pTj1_incl;

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2015_I1364361);


}