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CMS_2016_I1454211

Boosted $t\bar{t}$ in $pp$ collisions at $\sqrt{s} = 8 \text{TeV}$
Experiment: CMS (LHC)
Inspire ID: 1454211
Status: VALIDATED
Authors:
  • Salvatore Rappoccio
  • Maral Alyari
  • Julia Thom
  • Louise Skinnari
  • Susan Dittmer
  • Matthew Bellis
References:
  • CMS-PAS-TOP-14-012 (PAS)
  • CERN-EP-2016-078 (paper)
Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • $pp$ QCD interactions at $\sqrt{s} = 8 \text{TeV} with $t\bar{t}$ process. Data collected by CMS during the year 2012. Boosted topology restricts phase space, requiring high statistics in a single run or custom merging of the YODA files.

The cross section for pair production of top quarks with high transverse momenta ($p_\mathrm{T} > 400$ \text{GeV}) is measured in 19.7 fb$^{-1}$ of $\mathrm{pp}$ collisions, collected with the CMS detector at $\sqrt{s} = 8 \text{TeV}$. The measurement is performed for lepton+jets events, where one top quark decays according to $t \rightarrow Wb \rightarrow \ell \nu b$, with $\ell$ denoting an electron or muon, and the second top quark decays to an hadronic final state and is reconstructed as a single large-radius jet and identified as a top quark candidate using jet substructure techniques. Integrated cross sections, as well as differential cross sections as a function of the top quark $p_\mathrm{T}$ and rapidity, are measured both at particle level within a fiducial region resembling the detector-level selections and at parton level. RIVET: This analysis is to be run on $t\bar{t}$ Monte Carlo. It utilizes the PartonicTops projection, which assumes top quarks in the event record. The analysis has been validated with Powheg+Pythia6. The parton-level phase space is defined by requiring two PartonicTops. Exactly one PartonicTop must decay directly to a muon or electron (no intermediate tau), and exactly one PartonicTop decays hadronically. For $t\bar{t}$ Monte Carlo, this is equivalent to requiring the event to be semileptonic at parton level. The parton-level top quark is defined as the hadronically decaying top. The parton-level top quark is required to have $p_\mathrm{T} > 400 \text{GeV}$. The particle-level phase space is defined using the following object definitions: - Lepton: A dressed electron or muon, meaning the lepton has been clustered with all photons within a cone of $R=0.1$. The DressedLepton projection is used to construct the dressed lepton. The lepton is required to have $p_\mathrm{T} > 45$ GeV and $|\eta| < 2.1$. - B Jet Candidate: Gen AK5 jets are formed by clustering the final state particles in the event using the anti-$k_{T}$ algorithm with distance parameter $R=0.5$. Neutrinos are excluded from the clustering, as are any particles included in the dressed lepton. The gen AK5 jet is required to have $p_{T} > 30$ GeV and $|\eta| < 2.4$. Gen AK5 jets in the same hemisphere as the lepton ($\Delta R(e/\mu, \mathrm{jet}) < \pi/2$) are defined as $b$-jet candidates. - Top Jet Candidate: Gen CA8 jets are formed by clustering the final state particles in the event using the Cambridge-Aachen algorithm with distance parameter $R=0.8$. Neutrinos are excluded from the clustering, as are any particles included in the dressed lepton. The gen CA8 jet is required to have $p_{T} > 30$ GeV and $|\eta| < 2.4$. Gen CA8 jets which have $p_{T} > 400$ GeV, 140 GeV $<$ mass $<$ 250 GeV, and are in the opposite hemisphere from the lepton ($\Delta{\rm R(e/\mu, jet)} > \pi/2$) are defined as top jet candidates. The particle-level phase space is defined by requiring $\geq 1$ b jet candidate, $\geq 1$ top jet candidate, and exactly one lepton. This is in addition to the parton-level semileptonic requirement. The highest-$p_\mathrm{T}$ top jet candidate is defined as the particle-level $t$ jet.

Source code: CMS_2016_I1454211.cc
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#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/PartonicTops.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/InvMassFinalState.hh"
#include "Rivet/Projections/MissingMomentum.hh"

namespace Rivet {


  /// Boosted ttbar in pp collisions at sqrtS = 8 TeV
  /// @todo Use persistent weight counters
  class CMS_2016_I1454211 : public Analysis {
  public:

    DEFAULT_RIVET_ANALYSIS_CTOR(CMS_2016_I1454211);


    // Set up projections and book histograms
    void init() {

      // Complete final state
      FinalState fs;

      // Partonic tops
      declare(PartonicTops(PartonicTops::ELECTRON, false), "ElectronPartonTops");
      declare(PartonicTops(PartonicTops::MUON, false),     "MuonPartonTops");
      declare(PartonicTops(PartonicTops::HADRONIC),        "HadronicPartonTops");

      // Projection for electrons and muons
      IdentifiedFinalState photons(fs, PID::PHOTON);

      const Cut leptonCuts = Cuts::pt > 45*GeV && Cuts::abseta < 2.1;

      IdentifiedFinalState el_id(fs, {{PID::ELECTRON, -PID::ELECTRON}});
      PromptFinalState electrons(el_id);
      DressedLeptons dressed_electrons(photons, electrons, 0.1, leptonCuts);
      declare(dressed_electrons, "DressedElectrons");

      IdentifiedFinalState mu_id(fs, {{PID::MUON, -PID::MUON}});
      PromptFinalState muons(mu_id);
      DressedLeptons dressed_muons(photons, muons, 0.1, leptonCuts);
      declare(dressed_muons, "DressedMuons");

      // Projection for jets
      VetoedFinalState fs_jets(fs);
      fs_jets.addVetoOnThisFinalState(dressed_muons);
      fs_jets.addVetoOnThisFinalState(dressed_electrons);
      fs_jets.vetoNeutrinos();
      declare(FastJets(fs_jets, FastJets::ANTIKT, 0.5), "ak5jets");
      declare(FastJets(fs_jets, FastJets::CAM, 0.8), "ca8jets");

      _hEl_topPt_parton          = bookHisto1D("d01-x01-y01"); // dsigma/dpt(top quark), el ch
      _hEl_topPt_particle        = bookHisto1D("d02-x01-y01"); // dsigma/dpt(top jet), el ch
      _hEl_topY_parton           = bookHisto1D("d03-x01-y01"); // dsigma/dy(top quark), el ch
      _hEl_topY_particle         = bookHisto1D("d04-x01-y01"); // dsigma/dy(top jet), el ch
      _hMu_topPt_parton          = bookHisto1D("d05-x01-y01"); // dsigma/dpt(top quark), mu ch
      _hMu_topPt_particle        = bookHisto1D("d06-x01-y01"); // dsigma/dpt(top jet), mu ch
      _hMu_topY_parton           = bookHisto1D("d07-x01-y01"); // dsigma/dy(top quark), mu ch
      _hMu_topY_particle         = bookHisto1D("d08-x01-y01"); // dsigma/dy(top jet), mu ch
      _hComb_topPt_parton        = bookHisto1D("d09-x01-y01"); // dsigma/dpt(top quark), comb ch
      _hComb_topPt_particle      = bookHisto1D("d10-x01-y01"); // dsigma/dpt(top jet), comb ch
      _hComb_topY_parton         = bookHisto1D("d11-x01-y01"); // dsigma/dy(top quark), comb ch
      _hComb_topY_particle       = bookHisto1D("d12-x01-y01"); // dsigma/dy(top jet), comb ch

      _hEl_topPt_parton_norm     = bookHisto1D("d13-x01-y01"); // 1/sigma dsigma/dpt(top quark), el ch
      _hEl_topPt_particle_norm   = bookHisto1D("d14-x01-y01"); // 1/sigma dsigma/dpt(top jet), el ch
      _hEl_topY_parton_norm      = bookHisto1D("d15-x01-y01"); // 1/sigma dsigma/dy(top quark), el ch
      _hEl_topY_particle_norm    = bookHisto1D("d16-x01-y01"); // 1/sigma dsigma/dy(top jet), el ch
      _hMu_topPt_parton_norm     = bookHisto1D("d17-x01-y01"); // 1/sigma dsigma/dpt(top quark), mu ch
      _hMu_topPt_particle_norm   = bookHisto1D("d18-x01-y01"); // 1/sigma dsigma/dpt(top jet), mu ch
      _hMu_topY_parton_norm      = bookHisto1D("d19-x01-y01"); // 1/sigma dsigma/dy(top quark), mu ch
      _hMu_topY_particle_norm    = bookHisto1D("d20-x01-y01"); // 1/sigma dsigma/dy(top jet), mu ch
      _hComb_topPt_parton_norm   = bookHisto1D("d21-x01-y01"); // 1/sigma dsigma/dpt(top quark), comb ch
      _hComb_topPt_particle_norm = bookHisto1D("d22-x01-y01"); // 1/sigma dsigma/dpt(top jet), comb ch
      _hComb_topY_parton_norm    = bookHisto1D("d23-x01-y01"); // 1/sigma dsigma/dy(top quark), comb ch
      _hComb_topY_particle_norm  = bookHisto1D("d24-x01-y01"); // 1/sigma dsigma/dy(top jet), comb ch

      _hMu_cutflow = bookHisto1D("mu_cutflow", 7, -0.5, 6.5);
      _hEl_cutflow = bookHisto1D("el_cutflow", 7, -0.5, 6.5);
    }


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

       // Total-events cutflow entries
      _hMu_cutflow->fill(0.);
      _hEl_cutflow->fill(0.);

      // Do parton-level selection and channel determination
      int partonCh = 0; //0 non-semi-lep, 1 muon, 2 electron
      const Particles muonpartontops = apply<ParticleFinder>(event, "MuonPartonTops").particlesByPt();
      const Particles electronpartontops = apply<ParticleFinder>(event, "ElectronPartonTops").particlesByPt();
      if (electronpartontops.size() == 0 && muonpartontops.size() == 1) partonCh = 1;
      else if (electronpartontops.size() == 1 && muonpartontops.size() == 0) partonCh = 2;
      else vetoEvent;
      const Particles hadronicpartontops = apply<ParticleFinder>(event, "HadronicPartonTops").particlesByPt();
      if (hadronicpartontops.size() != 1) vetoEvent;

      if (partonCh == 1) _hMu_cutflow->fill(1.); // muon at parton level
      if (partonCh == 2) _hEl_cutflow->fill(1.); // electron at parton level

      // Get hadronic parton-level top
      const FourMomentum& partonTopP4 = hadronicpartontops.front();

      // Do particle-level selection and channel determination
      const DressedLeptons& dressed_electrons = apply<DressedLeptons>(event, "DressedElectrons");
      const DressedLeptons& dressed_muons = apply<DressedLeptons>(event, "DressedMuons");

      bool passParticleLep = false, passParticleTop = false;
      FourMomentum lepton, particleTopP4;
      if (partonCh == 1 && dressed_muons.dressedLeptons().size() == 1 && dressed_electrons.dressedLeptons().size() == 0) {
        passParticleLep = true;
        _hMu_cutflow->fill(3.); //muon at particle level
        lepton = dressed_muons.dressedLeptons()[0].momentum();
      }
      if (partonCh == 2 && dressed_muons.dressedLeptons().size() == 0 && dressed_electrons.dressedLeptons().size() == 1) {
        passParticleLep = true;
        _hEl_cutflow->fill(3.); //electron at particle level
        lepton = dressed_electrons.dressedLeptons()[0].momentum();
      }

      if (passParticleLep) {

        // Jet cuts
        Cut jetCuts = Cuts::pt > 30*GeV && Cuts::abseta < 2.4;
        Jets genBjets, genTjets;
        int nGenBjets = 0, nGenTjets = 0;

        const FastJets& AK5jets = apply<FastJets>(event, "ak5jets");
        for (const Jet& jet : AK5jets.jetsByPt(jetCuts)) {
          if (deltaR(jet, lepton) > M_PI / 2.0) continue;
          if (deltaR(jet, lepton) < 0.1) continue;
          genBjets.push_back(jet);
          nGenBjets += 1;
        }

        const FastJets& CA8jets = apply<FastJets>(event, "ca8jets");
        for (const Jet& jet : CA8jets.jetsByPt(jetCuts)) {
          if (deltaR(jet, lepton) < M_PI / 2.0) continue;
          if (jet.mass() < 140*GeV) continue;
          if (jet.mass() > 250*GeV) continue;
          genTjets.push_back(jet);
          nGenTjets += 1;
        }

        if (nGenBjets >=1) {
          if (partonCh == 1) _hMu_cutflow->fill(4.); // muon at parton level
          if (partonCh == 2) _hEl_cutflow->fill(4.); // electron at parton level
          if (nGenTjets >= 1) {
            passParticleTop = true;
            if (partonCh == 1) _hMu_cutflow->fill(5.); // muon at parton level
            if (partonCh == 2) _hEl_cutflow->fill(5.); // electron at parton level
            particleTopP4 = genTjets[0];
          }
        }
      }

      const double weight = event.weight();
      if (partonCh == 1) {
        _nMu += weight;
        _hMu_topPt_parton->fill(partonTopP4.pT()/GeV, weight);
        _hMu_topPt_parton_norm->fill(partonTopP4.pT()/GeV, weight);
        _hComb_topPt_parton->fill(partonTopP4.pT()/GeV, weight);
        _hComb_topPt_parton_norm->fill(partonTopP4.pT()/GeV, weight);

        if (partonTopP4.pT() >= 400*GeV) {
          _nPassParton_mu += weight;
          _hMu_cutflow->fill(2.);
          _hMu_topY_parton->fill(partonTopP4.rapidity(), weight);
          _hMu_topY_parton_norm->fill(partonTopP4.rapidity(), weight);
          _hComb_topY_parton->fill(partonTopP4.rapidity(), weight);
          _hComb_topY_parton_norm->fill(partonTopP4.rapidity(), weight);
        }

        if (passParticleTop) {
          _hMu_topPt_particle->fill(particleTopP4.pT()/GeV, weight);
          _hMu_topPt_particle_norm->fill(particleTopP4.pT()/GeV, weight);
          _hComb_topPt_particle->fill(particleTopP4.pT()/GeV, weight);
          _hComb_topPt_particle_norm->fill(particleTopP4.pT()/GeV, weight);

          if (particleTopP4.pT() >= 400*GeV) {
            _nPassParticle_mu += weight;
            _hMu_cutflow->fill(6.);
            _hMu_topY_particle->fill(particleTopP4.rapidity(), weight);
            _hMu_topY_particle_norm->fill(particleTopP4.rapidity(), weight);
            _hComb_topY_particle->fill(particleTopP4.rapidity(), weight);
            _hComb_topY_particle_norm->fill(particleTopP4.rapidity(), weight);
          }
        }
      }

      if (partonCh == 2){
        _nEl += weight;
        _hEl_topPt_parton->fill(partonTopP4.pT()/GeV, weight);
        _hEl_topPt_parton_norm->fill(partonTopP4.pT()/GeV, weight);
        _hComb_topPt_parton->fill(partonTopP4.pT()/GeV, weight);
        _hComb_topPt_parton_norm->fill(partonTopP4.pT()/GeV, weight);

        if (partonTopP4.pT() >= 400*GeV) {
          _nPassParton_el += weight;
          _hEl_cutflow->fill(2.);
          _hEl_topY_parton->fill(partonTopP4.rapidity(), weight);
          _hEl_topY_parton_norm->fill(partonTopP4.rapidity(), weight);
          _hComb_topY_parton->fill(partonTopP4.rapidity(), weight);
          _hComb_topY_parton_norm->fill(partonTopP4.rapidity(), weight);
        }

        if (passParticleTop) {
          _hEl_topPt_particle->fill(particleTopP4.pT()/GeV, weight);
          _hEl_topPt_particle_norm->fill(particleTopP4.pT()/GeV, weight);
          _hComb_topPt_particle->fill(particleTopP4.pT()/GeV, weight);
          _hComb_topPt_particle_norm->fill(particleTopP4.pT()/GeV, weight);

          if (particleTopP4.pT() >= 400*GeV) {
            _nPassParticle_el += weight;
            _hEl_cutflow->fill(6.);
            _hEl_topY_particle->fill(particleTopP4.rapidity(), weight);
            _hEl_topY_particle_norm->fill(particleTopP4.rapidity(), weight);
            _hComb_topY_particle->fill(particleTopP4.rapidity(), weight);
            _hComb_topY_particle_norm->fill(particleTopP4.rapidity(), weight);
          }
        }
      }
    }


    void finalize() {

      normalize({_hMu_topPt_parton_norm, _hMu_topY_parton_norm, _hEl_topPt_parton_norm,
            _hEl_topY_parton_norm, _hComb_topPt_parton_norm, _hComb_topY_parton_norm}, 1.0, false);
      normalize({_hMu_topPt_particle_norm, _hMu_topY_particle_norm, _hEl_topPt_particle_norm,
            _hEl_topY_particle_norm, _hComb_topPt_particle_norm, _hComb_topY_particle_norm}, 1.0, false);

      scale(_hMu_topPt_particle, crossSection()/femtobarn / sumOfWeights());
      scale(_hEl_topPt_particle, crossSection()/femtobarn / sumOfWeights());
      scale(_hMu_topY_particle, crossSection()/femtobarn / sumOfWeights());
      scale(_hEl_topY_particle, crossSection()/femtobarn / sumOfWeights());
      scale(_hComb_topPt_particle, crossSection()/femtobarn / sumOfWeights());
      scale(_hComb_topY_particle, crossSection()/femtobarn / sumOfWeights());

      scale(_hMu_topPt_parton, crossSection()/femtobarn / sumOfWeights());
      scale(_hEl_topPt_parton, crossSection()/femtobarn / sumOfWeights());
      scale(_hMu_topY_parton, crossSection()/femtobarn / sumOfWeights());
      scale(_hEl_topY_parton, crossSection()/femtobarn / sumOfWeights());
      scale(_hComb_topPt_parton, crossSection()/femtobarn / sumOfWeights());
      scale(_hComb_topY_parton, crossSection()/femtobarn / sumOfWeights());

    }


  private:

    Histo1DPtr _hMu_topPt_parton, _hMu_topY_parton, _hEl_topPt_parton, _hEl_topY_parton, _hComb_topPt_parton, _hComb_topY_parton;
    Histo1DPtr _hMu_topPt_particle, _hMu_topY_particle, _hEl_topPt_particle, _hEl_topY_particle, _hComb_topPt_particle, _hComb_topY_particle;
    Histo1DPtr _hMu_topPt_parton_norm, _hMu_topY_parton_norm, _hEl_topPt_parton_norm, _hEl_topY_parton_norm, _hComb_topPt_parton_norm, _hComb_topY_parton_norm;
    Histo1DPtr _hMu_topPt_particle_norm, _hMu_topY_particle_norm, _hEl_topPt_particle_norm, _hEl_topY_particle_norm, _hComb_topPt_particle_norm, _hComb_topY_particle_norm;
    Histo1DPtr _hMu_cutflow, _hEl_cutflow;

    double _nMu = 0., _nEl = 0.;
    double _nPassParton_mu = 0.,_nPassParton_el = 0.;
    double _nPassParticle_mu = 0., _nPassParticle_el = 0.;

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(CMS_2016_I1454211);

}