Rivet Analyses Reference

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// -*- C++ -*
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/MissingMomentum.hh"

#include "fastjet/contrib/Njettiness.hh"
#include "fastjet/contrib/Nsubjettiness.hh"
#include "fastjet/contrib/NjettinessPlugin.hh"

namespace Rivet {


  class ATLAS_2017_I1614149 : public Analysis {
  public:

    /// Constructor
    ///@brief: Resolved and boosted ttbar l+jets cross sections at 13 TeV
    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2017_I1614149);

    void init() {
      // Eta ranges
      Cut eta_full = (Cuts::abseta < 5.0);
      Cut lep_cuts = (Cuts::abseta < 2.5) && (Cuts::pT > 25*GeV);

      // All final state particles
      FinalState fs(eta_full);

      IdentifiedFinalState all_photons(fs);
      all_photons.acceptIdPair(PID::PHOTON);

      // Get photons to dress leptons
      IdentifiedFinalState ph_id(fs);
      ph_id.acceptIdPair(PID::PHOTON);

      // Projection to find the electrons
      IdentifiedFinalState el_id(fs);
      el_id.acceptIdPair(PID::ELECTRON);

      PromptFinalState photons(ph_id);
      photons.acceptTauDecays(true);
      declare(photons, "photons");

      PromptFinalState electrons(el_id);
      electrons.acceptTauDecays(true);
      DressedLeptons dressedelectrons(photons, electrons, 0.1, lep_cuts);
      declare(dressedelectrons, "elecs");
      DressedLeptons ewdressedelectrons(all_photons, electrons, 0.1, eta_full);

      // Projection to find the muons
      IdentifiedFinalState mu_id(fs);
      mu_id.acceptIdPair(PID::MUON);

      PromptFinalState muons(mu_id);
      muons.acceptTauDecays(true);
      DressedLeptons dressedmuons(photons, muons, 0.1, lep_cuts);
      declare(dressedmuons, "muons");
      DressedLeptons ewdressedmuons(all_photons, muons, 0.1, eta_full);

      // Projection to find MET
      declare(MissingMomentum(fs), "MET");

      // remove prompt neutrinos from jet clustering
      IdentifiedFinalState nu_id(fs);
      nu_id.acceptNeutrinos();
      PromptFinalState neutrinos(nu_id);
      neutrinos.acceptTauDecays(true);

      // Jet clustering.
      VetoedFinalState vfs(fs);
      vfs.addVetoOnThisFinalState(ewdressedelectrons);
      vfs.addVetoOnThisFinalState(ewdressedmuons);
      vfs.addVetoOnThisFinalState(neutrinos);
      FastJets jets(vfs, FastJets::ANTIKT, 0.4, JetAlg::Muons::ALL, JetAlg::Invisibles::ALL);
      declare(jets, "jets");

      // Addition of the large-R jets
      VetoedFinalState vfs1(fs);
      vfs1.addVetoOnThisFinalState(neutrinos);
      FastJets fjets(vfs1, FastJets::ANTIKT, 1.);
      fjets.useInvisibles(JetAlg::Invisibles::NONE);
      fjets.useMuons(JetAlg::Muons::NONE);
      declare(fjets, "fjets");

      bookHists("top_pt_res", 15);
      bookHists("top_absrap_res", 17);
      bookHists("ttbar_pt_res", 19);
      bookHists("ttbar_absrap_res", 21);
      bookHists("ttbar_m_res", 23);
      bookHists("top_pt_boost", 25);
      bookHists("top_absrap_boost", 27);

    }


    void analyze(const Event& event) {

      // Get the selected objects, using the projections.
      vector<DressedLepton> electrons = apply<DressedLeptons>(event, "elecs").dressedLeptons();
      vector<DressedLepton> muons     = apply<DressedLeptons>(event, "muons").dressedLeptons();
      const Jets& jets  = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 25*GeV && Cuts::abseta < 2.5);
      const PseudoJets& all_fjets  = apply<FastJets>(event, "fjets").pseudoJetsByPt();

      // get MET
      const Vector3 met = apply<MissingMomentum>(event, "MET").vectorMPT();

      Jets bjets, lightjets;
      for (const Jet& jet : jets) {
        bool b_tagged = jet.bTags(Cuts::pT > 5*GeV).size();
        if ( b_tagged && bjets.size() < 2)  bjets +=jet;
        else lightjets += jet;
      }

      // Implementing large-R jets definition
      // trim the jets
      PseudoJets trimmed_fatJets;
      float Rfilt = 0.2;
      float pt_fraction_min = 0.05;
      fastjet::Filter trimmer(fastjet::JetDefinition(fastjet::kt_algorithm, Rfilt), fastjet::SelectorPtFractionMin(pt_fraction_min));
      for (PseudoJet pjet : all_fjets)  trimmed_fatJets += trimmer(pjet);
      trimmed_fatJets = fastjet::sorted_by_pt(trimmed_fatJets);
      PseudoJets trimmed_jets;
      for (unsigned int i = 0; i < trimmed_fatJets.size(); ++i) {
        FourMomentum tj_mom = momentum(trimmed_fatJets[i]);
        if (tj_mom.pt() <= 300*GeV)  continue;
        if (tj_mom.abseta() >= 2.0)  continue;
        trimmed_jets.push_back(trimmed_fatJets[i]);
      }

      bool single_electron = (electrons.size() == 1) && (muons.empty());
      bool single_muon = (muons.size() == 1) && (electrons.empty());

      DressedLepton *lepton = NULL;
      if (single_electron)   lepton = &electrons[0];
      else if (single_muon)  lepton = &muons[0];

      if (!single_electron && !single_muon) vetoEvent;

      bool pass_resolved = true;
      bool num_b_tagged_jets = (bjets.size() == 2);
      if (!num_b_tagged_jets)  pass_resolved = false;

      if (jets.size() < 4) pass_resolved = false;

      bool pass_boosted = true;
      int fatJetIndex = -1;
      bool passTopTag = false;
      bool passDphi = false;
      bool passAddJet = false;
      bool goodLepJet = false;
      bool lepbtag = false;
      bool hadbtag=false;
      vector<int> lepJetIndex;
      vector<int> jet_farFromHadTopJetCandidate;
      if (met.mod() < 20*GeV)  pass_boosted = false;
      if (pass_boosted) {
        double transmass = _mT(lepton->momentum(), met);
        if (transmass + met.mod() < 60*GeV)  pass_boosted = false;
      }
      if (pass_boosted) {
        if (trimmed_jets.size() >= 1) {
          for (unsigned int j = 0; j<trimmed_jets.size(); ++j) {
            if (tau32( trimmed_jets.at(j), 1. ) < 0.75 &&
                momentum(trimmed_jets.at(j)).mass() > 100*GeV &&
                momentum(trimmed_jets.at(j)).pt() > 300*GeV &&
                momentum(trimmed_jets.at(j)).pt() < 1500*GeV &&
                fabs(momentum(trimmed_jets.at(j)).eta()) < 2.) {
              passTopTag = true;
              fatJetIndex = j;
              break;
            }
          }
        }
      }
      if(!passTopTag && fatJetIndex == -1)  pass_boosted = false;
      if (pass_boosted) {
        double dPhi_fatjet = deltaPhi(lepton->phi(), momentum(trimmed_jets.at(fatJetIndex)).phi());
        double dPhi_fatjet_lep_cut  = 1.0; //2.3
        if (dPhi_fatjet > dPhi_fatjet_lep_cut ) {
          passDphi = true;
        }
      }
      if (!passDphi)   pass_boosted = false;
      if (bjets.empty())   pass_boosted = false;
      if (pass_boosted) {
        for (unsigned int sj = 0; sj < jets.size(); ++sj) {
          double dR = deltaR(jets.at(sj).momentum(), momentum(trimmed_jets.at(fatJetIndex)));
          if(dR > 1.5) {
            passAddJet = true;
            jet_farFromHadTopJetCandidate.push_back(sj);
          }
        }
      }
      if (!passAddJet)  pass_boosted = false;
      if (pass_boosted) {
        for (int ltj : jet_farFromHadTopJetCandidate) {
          double dR_jet_lep = deltaR(jets.at(ltj).momentum(), lepton->momentum());
          double dR_jet_lep_cut = 2.0;//1.5
          if (dR_jet_lep < dR_jet_lep_cut) {
            lepJetIndex.push_back(ltj);
            goodLepJet = true;
          }
        }
      }
      if(!goodLepJet)  pass_boosted = false;
      if (pass_boosted) {
        for (int lepj : lepJetIndex) {
          lepbtag = jets.at(lepj).bTags(Cuts::pT > 5*GeV).size();
          if (lepbtag) break;
        }
      }
      double dR_fatBjet_cut = 1.0;
      if (pass_boosted) {
        for (const Jet& bjet : bjets) {
          hadbtag |= deltaR(momentum(trimmed_jets.at(fatJetIndex)), bjet) < dR_fatBjet_cut;
        }
      }

      if (!(lepbtag || hadbtag))  pass_boosted = false;

      FourMomentum pbjet1; //Momentum of bjet1
      FourMomentum pbjet2; //Momentum of bjet
      int Wj1index = -1, Wj2index = -1;

      if (pass_resolved) {

        if ( deltaR(bjets[0], *lepton) <= deltaR(bjets[1], *lepton) ) {
          pbjet1 = bjets[0].momentum();
          pbjet2 = bjets[1].momentum();
        } else {
          pbjet1 = bjets[1].momentum();
          pbjet2 = bjets[0].momentum();
        }

        double bestWmass = 1000.0*TeV;
        double mWPDG = 80.399*GeV;
        for (unsigned int i = 0; i < (lightjets.size() - 1); ++i) {
          for (unsigned int j = i + 1; j < lightjets.size(); ++j) {
            double wmass = (lightjets[i].momentum() + lightjets[j].momentum()).mass();
            if (fabs(wmass - mWPDG) < fabs(bestWmass - mWPDG)) {
              bestWmass = wmass;
              Wj1index = i;
              Wj2index = j;
            }
          }
        }

        FourMomentum pjet1 = lightjets[Wj1index].momentum();
        FourMomentum pjet2 = lightjets[Wj2index].momentum();

        // compute hadronic W boson
        FourMomentum pWhadron = pjet1 + pjet2;
        double pz = computeneutrinoz(lepton->momentum(), met);
        FourMomentum ppseudoneutrino( sqrt(sqr(met.x()) + sqr(met.y()) + sqr(pz)), met.x(), met.y(), pz);

        //compute leptonic, hadronic, combined pseudo-top
        FourMomentum ppseudotoplepton = lepton->momentum() + ppseudoneutrino + pbjet1;
        FourMomentum ppseudotophadron = pbjet2 + pWhadron;
        FourMomentum pttbar = ppseudotoplepton + ppseudotophadron;

        fillHists("top_pt_res", ppseudotophadron.pt()/GeV);
        fillHists("top_absrap_res", ppseudotophadron.absrap());
        fillHists("ttbar_pt_res", pttbar.pt()/GeV);
        fillHists("ttbar_absrap_res", pttbar.absrap());
        fillHists("ttbar_m_res", pttbar.mass()/GeV);
      }

      if (pass_boosted) {// Boosted selection
        double hadtop_pt= momentum(trimmed_jets.at(fatJetIndex)).pt() / GeV;
        double hadtop_absrap= momentum(trimmed_jets.at(fatJetIndex)).absrap();
        fillHists("top_pt_boost", hadtop_pt);
        fillHists("top_absrap_boost", hadtop_absrap);
      }
    }


    void finalize() {
      // Normalize to cross-section
      const double sf = (crossSection() / sumOfWeights());
      for (HistoMap::value_type& hist : _h) {
        scale(hist.second, sf);
        if (hist.first.find("_norm") != string::npos)  normalize(hist.second);
      }
    }


    void bookHists(std::string name, unsigned int index) {
      book(_h[name], index, 1 ,1);
      book(_h[name + "_norm"], index + 1, 1, 1);
    }


    void fillHists(std::string name, double value) {
      _h[name]->fill(value);
      _h[name + "_norm"]->fill(value);
    }


    double _mT(const FourMomentum &l, const Vector3 &met) const {
      return  sqrt(2.0 * l.pT() * met.mod() * (1 - cos(deltaPhi(l, met))) );
    }


    double tau32(const fastjet::PseudoJet &jet, double jet_rad) const {
      double alpha = 1.0;
      fjcontrib::NormalizedCutoffMeasure normalized_measure(alpha, jet_rad, 1000000);
      // WTA definition
      // Nsubjettiness::OnePass_WTA_KT_Axes wta_kt_axes;
      // as in JetSubStructure recommendations
      fjcontrib::KT_Axes kt_axes;

      /// NsubjettinessRatio uses the results from Nsubjettiness to calculate the ratio
      /// tau_N/tau_M, where N and M are specified by the user. The ratio of different tau values
      /// is often used in analyses, so this class is helpful to streamline code.
      fjcontrib::NsubjettinessRatio tau32_kt(3, 2, kt_axes, normalized_measure);

      double tau32 = tau32_kt.result(jet);
      return tau32;
    }


    double computeneutrinoz(const FourMomentum& lepton, const Vector3 &met) const {
      //computing z component of neutrino momentum given lepton and met
      double pzneutrino;
      double m_W = 80.399; // in GeV, given in the paper
      double k = (( sqr( m_W ) - sqr( lepton.mass() ) ) / 2 ) + (lepton.px() * met.x() + lepton.py() * met.y());
      double a = sqr ( lepton.E() )- sqr ( lepton.pz() );
      double b = -2*k*lepton.pz();
      double c = sqr( lepton.E() ) * sqr( met.mod() ) - sqr( k );
      double discriminant = sqr(b) - 4 * a * c;
      double quad[2] = { (- b - sqrt(discriminant)) / (2 * a), (- b + sqrt(discriminant)) / (2 * a) }; //two possible quadratic solns
      if (discriminant < 0)  pzneutrino = - b / (2 * a); //if the discriminant is negative
      else { //if the discriminant is greater than or equal to zero, take the soln with smallest absolute value
        double absquad[2];
        for (int n=0; n<2; ++n)  absquad[n] = fabs(quad[n]);
        if (absquad[0] < absquad[1])  pzneutrino = quad[0];
        else                          pzneutrino = quad[1];
      }

      return pzneutrino;
    }


  private:

    /// @name Objects that are used by the event selection decisions
    typedef map<string, Histo1DPtr> HistoMap;
    HistoMap _h;

  };


  RIVET_DECLARE_PLUGIN(ATLAS_2017_I1614149);

}