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ATLAS_2018_I1635273

W + jets production at 8 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1635273
Status: VALIDATED
Authors:
  • Valerie Lang
  • Christian Gutschow
References: Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • inclusive W -> ev production at 8 TeV

This paper presents a measurement of the $W$ boson production cross section and the $W^{+}/W^{-}$ cross-section ratio, both in association with jets, in proton-proton collisions at $\sqrt{s}=8$ TeV with the ATLAS experiment at the Large Hadron Collider. The measurement is performed in final states containing one electron and missing transverse momentum using data corresponding to an integrated luminosity of 20.2 fb$^{-1}$. Differential cross sections for events with at least one or two jets are presented for a range of observables, including jet transverse momenta and rapidities, the scalar sum of transverse momenta of the visible particles and the missing transverse momentum in the event, and the transverse momentum of the $W$ boson. For a subset of the observables, the differential cross sections of positively and negatively charged $W$ bosons are measured separately. In the cross-section ratio of $W^{+}/W^{-}$ the dominant systematic uncertainties cancel out, improving the measurement precision by up to a factor of nine. The observables and ratios selected for this paper provide valuable input for the up quark, down quark, and gluon parton distribution functions of the proton.

Source code: ATLAS_2018_I1635273.cc
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#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/InvisibleFinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"

namespace Rivet {

  /// @brief W + jets production at 8 TeV
  class ATLAS_2018_I1635273 : public Analysis {
  public:

    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2018_I1635273);

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

      // Get options from the new option system
      // Default uses electrons
      // EL looks for W->ev candidate
      // MU looks for W->mv candidate
      _mode = 0;
      if ( getOption("LMODE") == "EL" ) _mode = 0;
      if ( getOption("LMODE") == "MU" ) _mode = 1;

      FinalState fs;
      Cut cuts = Cuts::pT > 25*GeV && Cuts::abseta < 2.5;

      // Get photons to dress leptons
      // (Paper says "radiated photons", but there was
      // no promptness requirement in the analysis code)
      FinalState photons(Cuts::abspid == PID::PHOTON);

      // Get dressed leptons
      PromptFinalState leptons(Cuts::abspid == (_mode? PID::MUON : PID::ELECTRON), false);
      DressedLeptons dressedleptons(photons, leptons, 0.1, cuts, true);
      declare(dressedleptons, "DressedLeptons");

      // Get neutrinos for MET calculation
      declare(InvisibleFinalState(true), "InvFS"); // true = only allow prompt invisibles

      // jets
      FastJets jets(fs, FastJets::ANTIKT, 0.4, JetAlg::Muons::NONE);
      declare(jets, "Jets");

      // book histograms
      book(_h["N_incl_pb"],            1, 1, 1);
      book(_h["HT_1j_fb"],             6, 1, 1);
      book(_h["W_pt_1j_fb"],          11, 1, 1);
      book(_h["jet_pt1_1j_fb"],       16, 1, 1); 
      book(_h["jet_y1_1j_fb"],        21, 1, 1);
      book(_h["jet_pt2_2j_fb"],       26, 1, 1);
      book(_h["jet_y2_2j_fb"],        28, 1, 1);
      book(_h["DeltaRj12_2j_fb"],     30, 1, 1);
      book(_h["jet_mass12_2j_fb"],    32, 1, 1);
      book(_h["N_pb"],                34, 1, 1);
      book(_h["HT_2j_fb"],            36, 1, 1);
      book(_h["W_pt_2j_fb"],          41, 1, 1);
      book(_h["jet_pt1_2j_fb"],       46, 1, 1); 
      book(_h["el_eta_0j_pb"],        51, 1, 1);  
      book(_h["el_eta_1j_pb"],        56, 1, 1);   

      book(_h["Wplus_N_incl_pb"],      3, 1, 1);
      book(_h["Wplus_HT_1j_fb"],       8, 1, 1);
      book(_h["Wplus_W_pt_1j_fb"],    13, 1, 1);
      book(_h["Wplus_jet_pt1_1j_fb"], 18, 1, 1); 
      book(_h["Wplus_jet_y1_1j_fb"],  23, 1, 1);
      book(_h["Wplus_HT_2j_fb"],      38, 1, 1);
      book(_h["Wplus_W_pt_2j_fb"],    43, 1, 1);
      book(_h["Wplus_jet_pt1_2j_fb"], 48, 1, 1); 
      book(_h["Wplus_el_eta_0j_pb"],  53, 1, 1);
      book(_h["Wplus_el_eta_1j_pb"],  58, 1, 1);

      book(_h["Wminus_N_incl_pb"],     3, 1, 2);
      book(_h["Wminus_HT_1j_fb"],      8, 1, 2);
      book(_h["Wminus_W_pt_1j_fb"],   13, 1, 2);
      book(_h["Wminus_jet_pt1_1j_fb"],18, 1, 2);  
      book(_h["Wminus_jet_y1_1j_fb"], 23, 1, 2);
      book(_h["Wminus_HT_2j_fb"],     38, 1, 2);
      book(_h["Wminus_W_pt_2j_fb"],   43, 1, 2);
      book(_h["Wminus_jet_pt1_2j_fb"],48, 1, 2); 
      book(_h["Wminus_el_eta_0j_pb"], 53, 1, 2);
      book(_h["Wminus_el_eta_1j_pb"], 58, 1, 2);

      // and ratios
      book(_r["WplusOverWminus_N_incl_pb"],      3, 1, 3);
      book(_r["WplusOverWminus_HT_1j_fb"],       8, 1, 3);
      book(_r["WplusOverWminus_W_pt_1j_fb"],    13, 1, 3);
      book(_r["WplusOverWminus_jet_pt1_1j_fb"], 18, 1, 3);
      book(_r["WplusOverWminus_jet_y1_1j_fb"],  23, 1, 3);
      book(_r["WplusOverWminus_HT_2j_fb"],      38, 1, 3);
      book(_r["WplusOverWminus_W_pt_2j_fb"],    43, 1, 3);
      book(_r["WplusOverWminus_jet_pt1_2j_fb"], 48, 1, 3);
      book(_r["WplusOverWminus_el_eta_0j_pb"],  53, 1, 3);
      book(_r["WplusOverWminus_el_eta_1j_pb"],  58, 1, 3);

    }


    // Perform the per-event analysis
    void analyze(const Event& event) {
    
      // retrieve the dressed electrons
      const Particles& signal_leptons = apply<DressedLeptons>(event, "DressedLeptons").particlesByPt();
      if (signal_leptons.size() != 1 ) vetoEvent;
      const Particle& lepton = signal_leptons[0];

      // calulate MET and mT
      const Particles& invisibles = apply<InvisibleFinalState>(event, "InvFS").particles();
      FourMomentum pMET = sum(invisibles, Kin::mom, FourMomentum()).setZ(0);
      const double MET = pMET.pT() / GeV;
      const double mT = sqrt( 2 * lepton.Et() / GeV * MET * (1 - cos(deltaPhi(lepton,pMET))));
      if ( MET <= 25. ) vetoEvent;
      if ( mT  <= 40. ) vetoEvent;

      // retrieve jets
      Jets jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 30*GeV && Cuts::absrap < 4.4);
   
      idiscardIfAnyDeltaRLess(jets, signal_leptons, 0.2);

      // apply event selection on dR
      for (const Jet& j : jets) {
          if (deltaR(j, lepton) < 0.4) vetoEvent;
      }

      // calculate the observables
      const double w_pt = (lepton.momentum() + pMET).pT() / GeV;   
      const size_t njets = jets.size();
      double ST = sum(jets, Kin::pT, 0.0); // scalar pT sum of all selected jets
      const double HT = ST + lepton.pT() / GeV + MET; //missET;

      // fill W histograms		
      _h["N_pb"]->fill(njets);
      for (size_t i = 0; i <= njets; ++i) {
          _h["N_incl_pb"]->fill(i);
      }
      _h["el_eta_0j_pb"]->fill(lepton.abseta());

      if (njets > 0) {
          _h["HT_1j_fb"]->fill(HT);
          _h["W_pt_1j_fb"]->fill(w_pt);
          _h["jet_pt1_1j_fb"]->fill(jets[0].pT()/GeV);
          _h["jet_y1_1j_fb"]->fill(jets[0].absrap());
          _h["el_eta_1j_pb"]->fill(lepton.abseta());
      }
      if (njets > 1) {
          _h["HT_2j_fb"]->fill(HT);
          _h["W_pt_2j_fb"]->fill(w_pt);
          _h["jet_pt1_2j_fb"]->fill(jets[0].pT()/GeV);
          _h["DeltaRj12_2j_fb"]->fill(deltaR(jets[0],jets[1]));
          _h["jet_pt2_2j_fb"]->fill(jets[1].pT()/GeV);
          _h["jet_y2_2j_fb"]->fill(jets[1].absrap());
          _h["jet_mass12_2j_fb"]->fill( (jets[0].mom()+jets[1].mom()).mass()/GeV);
      }		
        // fill W+ histograms
      if (lepton.charge() > 0) {
          for (size_t i = 0; i <= njets; ++i) {
              _h["Wplus_N_incl_pb"]->fill(i);
          }
          _h["Wplus_el_eta_0j_pb"]->fill(lepton.abseta());
          if (njets > 0) {
              _h["Wplus_HT_1j_fb"]->fill(HT);
              _h["Wplus_W_pt_1j_fb"]->fill(w_pt);
              _h["Wplus_jet_pt1_1j_fb"]->fill(jets[0].pT()/GeV);
              _h["Wplus_jet_y1_1j_fb"]->fill(jets[0].absrap());
              _h["Wplus_el_eta_1j_pb"]->fill(lepton.abseta());
              if (njets > 1) {
                  _h["Wplus_HT_2j_fb"]->fill(HT);
                  _h["Wplus_W_pt_2j_fb"]->fill(w_pt);
                  _h["Wplus_jet_pt1_2j_fb"]->fill(jets[0].pT()/GeV);
              }		
          }
      }
      // fill W- histograms
      if (lepton.charge() < 0) {
        for (size_t i = 0; i <= njets; ++i) {
          _h["Wminus_N_incl_pb"]->fill(i);
        }
        _h["Wminus_el_eta_0j_pb"]->fill(lepton.abseta());
        if (njets > 0) {
          _h["Wminus_HT_1j_fb"]->fill(HT);
          _h["Wminus_W_pt_1j_fb"]->fill(w_pt);
          _h["Wminus_jet_pt1_1j_fb"]->fill(jets[0].pT()/GeV);
          _h["Wminus_jet_y1_1j_fb"]->fill(jets[0].absrap());
          _h["Wminus_el_eta_1j_pb"]->fill(lepton.abseta());
          if (njets > 1) {
            _h["Wminus_HT_2j_fb"]->fill(HT);
            _h["Wminus_W_pt_2j_fb"]->fill(w_pt);
            _h["Wminus_jet_pt1_2j_fb"]->fill(jets[0].pT()/GeV);
          }		
        }
      }
    }
    


    void finalize() {
      const double scalefactor_fb = crossSection() / sumOfWeights() / femtobarn;
      const double scalefactor_pb = crossSection() / sumOfWeights() / picobarn;

      for (auto& hit : _h){
        if (hit.first.find("_fb") != string::npos) scale(hit.second, scalefactor_fb);
        else                                       scale(hit.second, scalefactor_pb);
      }
      for (auto& rit : _r) {
        string ratio_label = "WplusOverWminus";
        string num_name   = rit.first;
        string denom_name = rit.first;
        num_name.replace(rit.first.find(ratio_label),ratio_label.length(),"Wplus");
        denom_name.replace(rit.first.find(ratio_label),ratio_label.length(),"Wminus");                   
        divide(_h[num_name], _h[denom_name], rit.second);
      }
    }

    protected:
      // Data members like post-cuts event weight counters go here
      size_t _mode;

    private:
      map<string, Histo1DPtr> _h;
      map<string, Scatter2DPtr> _r;
  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2018_I1635273);
}