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Rivet analyses reference

ATLAS_2021_I1849535

Inclusive 4-lepton cross sections at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1849535
Status: VALIDATED
Authors:
  • Max Goblirsch
  • Jon Butterworth
  • Louie Dartmoor Corpe
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • $p p \to \ell \ell \ell \ell + X$

Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015--2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single $Z$ boson production, Higgs boson production and on-shell $ZZ$ production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The $Z\to 4\ell$ branching fraction is extracted, giving a value of $\left(4.41 \pm 0.30\right) \times 10^{-6}$. Constraints on effective field theory parameters and a model based on a spontaneously broken $B-L$ gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information.

Source code: ATLAS_2021_I1849535.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"

namespace Rivet {

  /// @name M4lLineshape analysis
  class ATLAS_2021_I1849535 : public Analysis {
    public:

      /// Constructor
      DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2021_I1849535);

      void init() {

        // Selection
        Cut el_fid_sel = (Cuts::abseta < 2.47) && (Cuts::pT > 7*GeV); 
        Cut mu_fid_sel = (Cuts::abseta < 2.7) && (Cuts::pT > 5*GeV);

        PromptFinalState photons(Cuts::abspid == PID::PHOTON);
        PromptFinalState elecs(Cuts::abspid == PID::ELECTRON);
        PromptFinalState muons(Cuts::abspid == PID::MUON && mu_fid_sel);
        elecs.acceptTauDecays(true);
        muons.acceptTauDecays(true);


        // Final state including all charged particles
        declare(ChargedFinalState(), "CFS");

        DressedLeptons dressed_elecs(photons, elecs, 0.1, el_fid_sel, false);
        declare(dressed_elecs, "elecs");

        declare(muons, "muons");

        // Book histos
        book(_h["m4l_paper"],      1,1,1);
        book(_h["m4l_4mu_paper"],  2,1,1);
        book(_h["m4l_4e_paper"],   3,1,1);
        book(_h["m4l_2e2mu_paper"],4,1,1);

        book(_h["mZ1_Z_paper"],5,1,1);  
        book(_h["mZ1_H_paper"],6,1,1);
        book(_h["mZ1_offshell_paper"],7,1,1);
        book(_h["mZ1_ZZ_paper"],8,1,1);

        book(_h["mZ2_Z_paper"],9,1,1);
        book(_h["mZ2_H_paper"],10,1,1);
        book(_h["mZ2_offshell_paper"],11,1,1);
        book(_h["mZ2_ZZ_paper"],12,1,1);

        book(_h["ptZ1_Z_paper"],13,1,1);
        book(_h["ptZ1_H_paper"],14,1,1);
        book(_h["ptZ1_offshell_paper"],15,1,1); 
        book(_h["ptZ1_ZZ_paper"],16,1,1);

        book(_h["ptZ2_Z_paper"],17,1,1);
        book(_h["ptZ2_H_paper"],18,1,1);
        book(_h["ptZ2_offshell_paper"],19,1,1);
        book(_h["ptZ2_ZZ_paper"],20,1,1);

        book(_h["costhetastar1_Z_paper"],21,1,1);
        book(_h["costhetastar1_H_paper"],22,1,1);
        book(_h["costhetastar1_offshell_paper"],23,1,1);
        book(_h["costhetastar1_ZZ_paper"],24,1,1);

        book(_h["costhetastar2_Z_paper"],25,1,1);
        book(_h["costhetastar2_H_paper"],26,1,1);
        book(_h["costhetastar2_offshell_paper"],27,1,1);
        book(_h["costhetastar2_ZZ_paper"],28,1,1);

        book(_h["dy_Z1Z2_Z_paper"]  ,29,1,1);
        book(_h["dy_Z1Z2_H_paper"]  ,30,1,1);
        book(_h["dy_Z1Z2_offshell_paper"],31,1,1);
        book(_h["dy_Z1Z2_ZZ_paper"]  ,32,1,1);

        book(_h["dphi_Z1Z2_Z_paper"]  ,33,1,1);
        book(_h["dphi_Z1Z2_H_paper"]  ,34,1,1);
        book(_h["dphi_Z1Z2_offshell_paper"],35,1,1);
        book(_h["dphi_Z1Z2_ZZ_paper"]  ,36,1,1);

        book(_h["dphi_l1l2_Z_paper"]   ,37,1,1);
        book(_h["dphi_l1l2_H_paper"]  ,38,1,1);
        book(_h["dphi_l1l2_offshell_paper"],39,1,1);
        book(_h["dphi_l1l2_ZZ_paper"]  ,40,1,1);

        book(_h["m4l_ptslice1_paper"],41,1,1);
        book(_h["m4l_ptslice2_paper"],42,1,1);
        book(_h["m4l_ptslice3_paper"],43,1,1);
        book(_h["m4l_ptslice4_paper"],44,1,1);
        book(_h["m4l_ptslice5_paper"],45,1,1);

        book(_h["m4l_yslice1_paper"],46,1,1);
        book(_h["m4l_yslice2_paper"],47,1,1);
        book(_h["m4l_yslice3_paper"],48,1,1);
        book(_h["m4l_yslice4_paper"],49,1,1);
        book(_h["m4l_yslice5_paper"],50,1,1);

      }

      /// Generic dilepton candidate
      struct Dilepton : public ParticlePair {
        Dilepton() { }
        Dilepton(ParticlePair _particlepair) : ParticlePair(_particlepair) {
          assert(first.abspid() == second.abspid());
        }
        FourMomentum mom() const { return first.momentum() + second.momentum(); }
        operator FourMomentum() const { return mom(); }
        static bool cmppT(const Dilepton& lx, const Dilepton& rx) { return lx.mom().pT() < rx.mom().pT(); }
        int flavour() const { return first.abspid(); }
        double pTl1() const { return first.pT(); }
        double pTl2() const { return second.pT(); }
      };

      struct Quadruplet {
        Quadruplet (Dilepton z1, Dilepton z2): _z1(z1), _z2(z2) { }
        enum class FlavCombi { mm=0, ee, me, em, undefined };
        FourMomentum mom() const { return _z1.mom() + _z2.mom(); }
        Dilepton getZ1() const { return _z1; }
        Dilepton getZ2() const { return _z2; }
        Dilepton _z1, _z2;
        FlavCombi type() const {
          if (     _z1.flavour() == 13 && _z2.flavour() == 13) { return FlavCombi::mm; }
          else if (_z1.flavour() == 11 && _z2.flavour() == 11) { return FlavCombi::ee; } 
          else if (_z1.flavour() == 13 && _z2.flavour() == 11) { return FlavCombi::me; }
          else if (_z1.flavour() == 11 && _z2.flavour() == 13) { return FlavCombi::em; }
          else  return FlavCombi::undefined;
        }
      };
      bool passesTruthIsolation(Quadruplet quad, const Particles charged_tracks, Particles& truthLeptons ){
        bool pass =true;
        Particles leps;
        leps.push_back(quad._z1.first);
        leps.push_back(quad._z2.first);
        leps.push_back(quad._z1.second);
        leps.push_back(quad._z2.second);
        for (auto &lep : leps){
          double pTinCone = -lep.pT();
          for (const Particle& track : charged_tracks) {
            if (deltaR(lep.momentum(), track.momentum()) < 0.3)
              pTinCone += track.pT();
          }
          for (const Particle& tlep: truthLeptons) {
            float dR= deltaR(lep.momentum(),  tlep.momentum()); 
            if ( dR>0 && dR < 0.3)
              pTinCone -= tlep.pT();
          }
          if (pTinCone > 0.16* lep.pT()){
            pass=false;
          }
        }
        return pass;
      }

      std::vector<Quadruplet> getBestQuads(Particles& particles, bool drcut = true) {
        // H->ZZ->4l pairing
        // - Two same flavor opposite charged leptons
        // - Ambiguities in pairing are resolved by choosing the combination
        //     that results in the smaller value of |mll - mZ| for each pair successively
        std::vector<Quadruplet> quads {};

        size_t n_parts = particles.size();
        if (n_parts < 4)  return quads; 

        // STEP 1: find SFOS pairs 
        std::vector<Dilepton> SFOS;
        for (size_t i = 0; i < n_parts; ++i) {
          for (size_t j = 0; j < i; ++j) {
            if (particles[i].pid() == -particles[j].pid()) {
              // sort such that the negative lepton is listed first
              Dilepton sfos;
              if (particles[i].pid() > 0)  sfos = make_pair(particles[i], particles[j]);
              else                         sfos = make_pair(particles[j], particles[i]);

              if (sfos.mom().mass() > _ll_mass*GeV && (!drcut || deltaR(particles[i],particles[j]) > _dRll)) SFOS.push_back(sfos);
            }
          }
        }
        if (SFOS.size() < 2)  return quads;

        // now we sort the SFOS pairs
        std::sort(SFOS.begin(), SFOS.end(), [](const Dilepton& p1, const Dilepton& p2) {
            return fabs(p1.mom().mass() - Z_mass) < fabs(p2.mom().mass() - Z_mass);
            });

        //form all possible quadruplets, passing the pt cuts, the dR cuts and the mll cuts
        for (size_t k = 0; k < SFOS.size(); ++k) {
          for (size_t l = k+1; l < SFOS.size(); ++l) {
            if(drcut) {
              if (deltaR(SFOS[k].first.mom(),  SFOS[l].first.mom())  < _dRll)  continue;
              if (deltaR(SFOS[k].first.mom(),  SFOS[l].second.mom()) < _dRll)  continue;
              if (deltaR(SFOS[k].second.mom(), SFOS[l].first.mom())  < _dRll)  continue;
              if (deltaR(SFOS[k].second.mom(), SFOS[l].second.mom()) < _dRll)  continue;
            }
            if ( (SFOS[k].first.pid()   == -SFOS[l].first.pid())  && ((SFOS[k].first.mom()  + SFOS[l].first.mom()).mass()  < _ll_mass*GeV)) continue;
            if ( (SFOS[k].first.pid()   == -SFOS[l].second.pid()) && ((SFOS[k].first.mom()  + SFOS[l].second.mom()).mass() < _ll_mass*GeV)) continue;
            if ( (SFOS[k].second.pid()  == -SFOS[l].first.pid())  && ((SFOS[k].second.mom() + SFOS[l].first.mom()).mass()  < _ll_mass*GeV)) continue;
            if ( (SFOS[k].second.pid()  == -SFOS[l].second.pid()) && ((SFOS[k].second.mom() + SFOS[l].second.mom()).mass() < _ll_mass*GeV)) continue;

            //think technically this should happen before quad formation now and with all leptons not just those in quad so commenting out
            //std::vector<double> lep_pt { SFOS[k].pTl1(), SFOS[k].pTl2(), SFOS[l].pTl1(), SFOS[l].pTl2() };
            //std::sort(lep_pt.begin(), lep_pt.end(), std::greater<double>()); 
            //if (!(lep_pt[0] > _pt_lep1*GeV && lep_pt[1] > _pt_lep2*GeV && lep_pt[2] > _pt_lep3*GeV)) continue;
            quads.push_back( Quadruplet(SFOS[k], SFOS[l]) );
          }
        }
        return quads;
      }

      bool passPtLeptons(const Particles& particles) {
        size_t n_parts = particles.size();
        if (n_parts < 4)  return false;
        // cut on pT of leptons
        return ( particles[0].mom().pt() > _pt_lep1*GeV && particles[1].mom().pt() > _pt_lep2*GeV && particles[2].mom().pt() > _pt_lep3*GeV) ;
      }


      // Do the analysis
      void analyze(const Event& event) {

        const Particles charged_tracks    = apply<ChargedFinalState>(event, "CFS").particles();


        //preselection of leptons for ZZ-> llll final state
        Particles dressed_leptons;
        for (auto lep : apply<FinalState>(event, "muons").particles()) { dressed_leptons.push_back(lep); }
        for (auto lep : apply<DressedLeptons>(event, "elecs").dressedLeptons()) { dressed_leptons.push_back(lep); }



        // sort to put highest pT first
        std::sort(dressed_leptons.begin(), dressed_leptons.end(), [](const Particle& l1, const Particle& l2) {
            return l1.pt() > l2.pt();
            });

        auto foundDressedNoDrll = getBestQuads(dressed_leptons,false);

        //now doing pt cut before quad formation so also apply this here
        if (!passPtLeptons(dressed_leptons)) vetoEvent;

        auto foundDressed = getBestQuads(dressed_leptons);
        // if we don't find any quad, we can stop here 
        if (foundDressed.empty())  vetoEvent;
        if (!passesTruthIsolation(foundDressed[0], charged_tracks, dressed_leptons)) vetoEvent;

        double m4l = foundDressed[0].mom().mass()/GeV;
        double pt4l = foundDressed[0].mom().pT()/GeV;
        double y4l = foundDressed[0].mom().absrap();
        double mZ1 = foundDressed[0].getZ1().mom().mass()/GeV;
        double mZ2 = foundDressed[0].getZ2().mom().mass()/GeV;
        double ptZ1 = foundDressed[0].getZ1().mom().pT()/GeV;
        double ptZ2 = foundDressed[0].getZ2().mom().pT()/GeV;
        double dy_Z1Z2 = fabs(foundDressed[0].getZ1().mom().rapidity() - foundDressed[0].getZ2().mom().rapidity());
        double dphi_Z1Z2 = deltaPhi(foundDressed[0].getZ1().mom(),foundDressed[0].getZ2().mom());
        double dphi_l1l2 = deltaPhi(dressed_leptons[0].mom(),dressed_leptons[1].mom());

        _h["m4l_paper"]->fill(m4l);
        if (     pt4l <  10.)	  _h["m4l_ptslice1_paper"]->fill(m4l);
        else if (pt4l <  20.)	  _h["m4l_ptslice2_paper"]->fill(m4l);
        else if (pt4l < 50.)	  _h["m4l_ptslice3_paper"]->fill(m4l);
        else if (pt4l < 100.)	  _h["m4l_ptslice4_paper"]->fill(m4l);
        else if (pt4l < 600.)	  _h["m4l_ptslice5_paper"]->fill(m4l); 

        if (y4l < 0.3)	  _h["m4l_yslice1_paper"]->fill(m4l);
        else if (y4l < 0.6)	  _h["m4l_yslice2_paper"]->fill(m4l);
        else if (y4l < 0.9)	  _h["m4l_yslice3_paper"]->fill(m4l);
        else if (y4l < 1.2)	  _h["m4l_yslice4_paper"]->fill(m4l);
        else if (y4l < 2.5)	  _h["m4l_yslice5_paper"]->fill(m4l);


        Quadruplet::FlavCombi flavour = foundDressed[0].type();
        if (     flavour == Quadruplet::FlavCombi::mm) { _h["m4l_4mu_paper"]->fill(m4l); }
        else if (flavour == Quadruplet::FlavCombi::ee) { _h["m4l_4e_paper"]->fill(m4l); }
        else if (flavour == Quadruplet::FlavCombi::me || flavour == Quadruplet::FlavCombi::em) {
          _h["m4l_2e2mu_paper"]->fill(m4l);
        }

        // polarization variables
        // Get four-momentum of the first lepton pair
        const FourMomentum pcom = foundDressed.at(0).getZ1().mom();
        const Vector3 betacom = pcom.betaVec();
        const Vector3 unitboostvec = betacom.unit();
        const LorentzTransform comboost = LorentzTransform::mkFrameTransformFromBeta(betacom);
        // Get four-momentum of the negative lepton w.r.t. the first lepton pair
        const FourMomentum p1com = comboost.transform(foundDressed.at(0).getZ1().first.mom());
        float costhetastar1 = cos(p1com.p3().angle(unitboostvec));

        // Get four-momentum of the second lepton pair
        const FourMomentum pcom2 = foundDressed.at(0).getZ2().mom();
        const Vector3 betacom2 = pcom2.betaVec();
        const Vector3 unitboostvec2 = betacom2.unit();
        const LorentzTransform comboost2 = LorentzTransform::mkFrameTransformFromBeta(betacom2);
        // Get four-momentum of the negative lepton w.r.t. the second lepton pair
        const FourMomentum p2com = comboost2.transform(foundDressed.at(0).getZ2().first.mom());
        float  costhetastar2 = cos(p2com.p3().angle(unitboostvec2));

        //fill m4l binned variables
        if (60 < m4l && m4l < 100.) {
          _h["mZ1_Z_paper"]->fill(mZ1);
          _h["mZ2_Z_paper"]->fill(mZ2);
          _h["ptZ1_Z_paper"]->fill(ptZ1);
          _h["ptZ2_Z_paper"]->fill(ptZ2);
          _h["dy_Z1Z2_Z_paper"]->fill(dy_Z1Z2);
          _h["dphi_Z1Z2_Z_paper"]->fill(dphi_Z1Z2);
          _h["dphi_l1l2_Z_paper"]->fill(dphi_l1l2);
          _h["costhetastar1_Z_paper"]->fill(costhetastar1 );
          _h["costhetastar2_Z_paper"]->fill(costhetastar2 );
        }
        else if(120 < m4l && m4l < 130 ){
          _h["mZ1_H_paper"]->fill(mZ1);
          _h["mZ2_H_paper"]->fill(mZ2);
          _h["ptZ1_H_paper"]->fill(ptZ1);
          _h["ptZ2_H_paper"]->fill(ptZ2);
          _h["dy_Z1Z2_H_paper"]->fill(dy_Z1Z2);
          _h["dphi_Z1Z2_H_paper"]->fill(dphi_Z1Z2);
          _h["dphi_l1l2_H_paper"]->fill(dphi_l1l2);
          _h["costhetastar1_H_paper"]->fill(costhetastar1 );
          _h["costhetastar2_H_paper"]->fill(costhetastar2 );
        }
        else if(180 < m4l && m4l < 2000){
          _h["mZ1_ZZ_paper"]->fill(mZ1);
          _h["mZ2_ZZ_paper"]->fill(mZ2);
          _h["ptZ1_ZZ_paper"]->fill(ptZ1);
          _h["ptZ2_ZZ_paper"]->fill(ptZ2);
          _h["dy_Z1Z2_ZZ_paper"]->fill(dy_Z1Z2);
          _h["dphi_Z1Z2_ZZ_paper"]->fill(dphi_Z1Z2);
          _h["dphi_l1l2_ZZ_paper"]->fill(dphi_l1l2);
          _h["costhetastar1_ZZ_paper"]->fill(costhetastar1 );
          _h["costhetastar2_ZZ_paper"]->fill(costhetastar2 );
        }
        else{
          _h["mZ1_offshell_paper"]->fill(mZ1);
          _h["mZ2_offshell_paper"]->fill(mZ2);
          _h["ptZ1_offshell_paper"]->fill(ptZ1);
          _h["ptZ2_offshell_paper"]->fill(ptZ2);
          _h["dy_Z1Z2_offshell_paper"]->fill(dy_Z1Z2);
          _h["dphi_Z1Z2_offshell_paper"]->fill(dphi_Z1Z2);
          _h["dphi_l1l2_offshell_paper"]->fill(dphi_l1l2);
          _h["costhetastar1_offshell_paper"]->fill(costhetastar1 );
          _h["costhetastar2_offshell_paper"]->fill(costhetastar2 );
        }

      }//end analysis

      /// Finalize
      void finalize() {
        const double sf = crossSection() / femtobarn / sumOfWeights();
        for (auto hist : _h) { scale(hist.second, sf); }
      }

    private:

      map<string, Histo1DPtr> _h;
      static constexpr double Z_mass = 91.1876;
      static constexpr float _pt_lep1 = 20.;
      static constexpr float _pt_lep2 = 10.;
      static constexpr float _pt_lep3 = 0.;
      static constexpr float _ll_mass = 5.;
      static constexpr float _dRll = 0.05;

  };  // end class ATLAS_2021_I1849535

  DECLARE_RIVET_PLUGIN(ATLAS_2021_I1849535);
}  // end namespace rivet