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ATLAS_2017_I1589844

$k_T$ splittings in $Z$ events at 8 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1589844
Status: VALIDATED
Authors:
  • Christian Gutschow
  • Frank Siegert
References: Beams: p+ p+
Beam energies: (4000.0, 4000.0) GeV
Run details:
  • $pp \to Z(\to ee/\mu\mu) +$ jets at 8 TeV

A measurement of the splitting scales occuring in the $k_\text{t}$ jet-clustering algorithm is presented for final states containing a $Z$ boson. The measurement is done using 20.2 fb$^{-1}$ of proton-proton collision data collected at a centre-of-mass energy of $\sqrt{s} = 8$ TeV by the ATLAS experiment at the LHC in 2012. The measurement is based on charged-particle track information, which is measured with excellent precision in the $p_\text{T}$ region relevant for the transition between the perturbative and the non-perturbative regimes. The data distributions are corrected for detector effects, and are found to deviate from state-of-the-art predictions in various regions of the observables. If no mode specified, will try to fill both electron and muon plots. If EL or MU is specified, only the relevant plots will be filled.

Source code: ATLAS_2017_I1589844.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {


  /// kT splittings in Z events at 8 TeV
  class ATLAS_2017_I1589844 : public Analysis {
  public:

    /// @name Constructors etc.
    //@{

    /// Constructors
    ATLAS_2017_I1589844(const string name="ATLAS_2017_I1589844",
                        const string ref_data="ATLAS_2017_I1589844") : Analysis(name) {
      setRefDataName(ref_data);
    }

    //@}


    /// @name Analysis methods
    //@{

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

      // Get options from the new option system
      _mode = 0;
      if ( getOption("LMODE") == "EL" ) _mode = 1;
      if ( getOption("LMODE") == "MU" ) _mode = 2;

      const FinalState fs;

      const Cut cuts_mu = (Cuts::pT > 25*GeV) && (Cuts::abseta < 2.4);
      const Cut cuts_el = Cuts::pT > 25*GeV && (Cuts::abseta <= 1.37 || (Cuts::abseta >= 1.52 && Cuts::abseta < 2.47));

      IdentifiedFinalState bare_mu(fs);
      bare_mu.acceptIdPair(PID::MUON);
      IdentifiedFinalState bare_el(fs);
      bare_el.acceptIdPair(PID::ELECTRON);
      const DressedLeptons muons(fs, bare_mu, 0.1, cuts_mu, true);
      const DressedLeptons elecs(fs, bare_el, 0.1, cuts_el, true);
      declare(muons, "muons");
      declare(elecs, "elecs");

      const ChargedFinalState cfs(Cuts::abseta < 2.5 && Cuts::pT > 0.4*GeV);
      VetoedFinalState jet_fs(cfs);
      jet_fs.addVetoOnThisFinalState(muons);
      jet_fs.addVetoOnThisFinalState(elecs);
      declare(FastJets(jet_fs, FastJets::KT, 0.4), "Kt04Jets");
      declare(FastJets(jet_fs, FastJets::KT, 1.0), "Kt10Jets");

      VetoedFinalState jet_fs_all(FinalState(Cuts::abseta < 2.5 && Cuts::pT > 0.4*GeV));
      jet_fs_all.addVetoOnThisFinalState(muons);
      jet_fs_all.addVetoOnThisFinalState(elecs);
      FastJets jetpro04_all(jet_fs_all, FastJets::KT, 0.4);
      jetpro04_all.useInvisibles();
      declare(jetpro04_all, "Kt04Jets_all");
      FastJets jetpro10_all(jet_fs_all, FastJets::KT, 1.0);
      jetpro10_all.useInvisibles();
      declare(jetpro10_all, "Kt10Jets_all");

      // Histograms with data binning
      _ndij = 8;
      for (size_t i = 0; i < _ndij; ++i) {
        if (_mode == 0 || _mode == 1) {
          string label = "el_d" + to_str(i) + "_kT4";
          _h[label] = bookHisto1D(i + 1, 1, 1);
          _h[label + "_all"] = bookHisto1D(i + 1, 1, 5);
          label = "el_d" + to_str(i) + "_kT10";
          _h[label] = bookHisto1D(i + 1, 1, 3);
          _h[label + "_all"] = bookHisto1D(i + 1, 1, 7);
        }
        if (_mode == 0 || _mode == 2) {
          string label = "mu_d" + to_str(i) + "_kT4";
          _h[label] = bookHisto1D(i + 1, 1, 2);
          _h[label + "_all"] = bookHisto1D(i + 1, 1, 6);
          label = "mu_d" + to_str(i) + "_kT10";
          _h[label] = bookHisto1D(i + 1, 1, 4);
          _h[label + "_all"] = bookHisto1D(i + 1, 1, 8);
        }
      }
    }


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

      // Check we have a Z candidate:
      const vector<DressedLepton>& muons = apply<DressedLeptons>(e, "muons").dressedLeptons();
      const vector<DressedLepton>& elecs = apply<DressedLeptons>(e, "elecs").dressedLeptons();

      bool e_ok = elecs.size() == 2 && muons.empty();
      bool m_ok = elecs.empty() && muons.size() == 2;
      if (_mode == 0 && !e_ok && !m_ok) vetoEvent;
      if (_mode == 1 && !e_ok )  vetoEvent;
      if (_mode == 2 && !m_ok )  vetoEvent;

      string lep_type = elecs.size()? "el_" : "mu_";

      const vector<DressedLepton>& leptons = elecs.size()? elecs : muons;
      if (leptons[0].charge()*leptons[1].charge() > 0) vetoEvent;

      const double dilepton_mass = (leptons[0].momentum() + leptons[1].momentum()).mass();
      if (!inRange(dilepton_mass, 71*GeV, 111*GeV)) vetoEvent;

      const double weight = e.weight();

      // Get kT splitting scales (charged particles only)
      const FastJets& jetpro04 = applyProjection<FastJets>(e, "Kt04Jets");
      const shared_ptr<fastjet::ClusterSequence> seq04 = jetpro04.clusterSeq();
      for (size_t i = 0; i < min(_ndij, (size_t)seq04->n_particles()); ++i) {
        const double dij = sqrt(seq04->exclusive_dmerge_max(i))/GeV;
        if (dij <= 0.0) continue;
        const string label = lep_type + "d" + to_str(i) + "_kT4";
        _h[label]->fill(dij, weight);
      }
      const FastJets& jetpro10 = applyProjection<FastJets>(e, "Kt10Jets");
      const shared_ptr<fastjet::ClusterSequence> seq10 = jetpro10.clusterSeq();
      for (size_t i = 0; i < min(_ndij, (size_t)seq10->n_particles()); ++i) {
        const double dij = sqrt(seq10->exclusive_dmerge_max(i))/GeV;
        if (dij <= 0.0) continue;
        const string label = lep_type + "d" + to_str(i) + "_kT10";
        _h[label]->fill(dij, weight);
      }

      // Get kT splitting scales (all particles)
      const FastJets& jetpro04_all = applyProjection<FastJets>(e, "Kt04Jets_all");
      const shared_ptr<fastjet::ClusterSequence> seq04_all = jetpro04_all.clusterSeq();
      for (size_t i = 0; i < min(_ndij, (size_t)seq04_all->n_particles()); ++i) {
        const double dij = sqrt(seq04_all->exclusive_dmerge_max(i))/GeV;
        if (dij <= 0.0) continue;
        const string label = lep_type + "d" + to_str(i) + "_kT4_all";
        _h[label]->fill(dij, weight);
      }
      const FastJets& jetpro10_all = applyProjection<FastJets>(e, "Kt10Jets_all");
      const shared_ptr<fastjet::ClusterSequence> seq10_all = jetpro10_all.clusterSeq();
      for (size_t i = 0; i < min(_ndij, (size_t)seq10_all->n_particles()); ++i) {
        const double dij = sqrt(seq10_all->exclusive_dmerge_max(i))/GeV;
        if (dij <= 0.0) continue;
        const string label = lep_type + "d" + to_str(i) + "_kT10_all";
        _h[label]->fill(dij, weight);
      }

    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double sf = crossSectionPerEvent();
      for (auto& kv : _h) scale(kv.second, sf);
    }

    //@}


  protected:

    // Data members like post-cuts event weight counters go here
    size_t _mode, _ndij;


  private:

    // Histograms
    map<string, Histo1DPtr> _h;

  };

  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2017_I1589844);
}