Rivet analyses

Lund jet plane with charged particles

Experiment: ATLAS (LHC)

Inspire ID: 1790256

Status: VALIDATED

Authors: - Deepak Kar

References: - arXiv: 2004.03540

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - pp -> dijet production at 13 TeV, pTHatMin cut of 200 GeV suggested.

The prevalence of hadronic jets at the LHC requires that a deep understanding of jet formation and structure is achieved in order to reach the highest levels of experimental and theoretical precision. There have been many measurements of jet substructure at the LHC and previous colliders, but the targeted observables mix physical effects from various origins. Based on a recent proposal to factorize physical effects, this Letter presents a double-differential cross-section measurement of the Lund jet plane using 139 fb⁻¹ of $\sqrt{s}=13$ TeV proton-proton collision data collected with the ATLAS detector using jets with transverse momentum above 675 GeV. The measurement uses charged particles to achieve a fine angular resolution and is corrected for acceptance and detector effects. Several parton shower Monte Carlo models are compared with the data. No single model is found to be in agreement with the measured data across the entire plane.

Source code:`ATLAS_2020_I1790256.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "fastjet/contrib/LundGenerator.hh"

namespace Rivet {


  /// @brief Lund jet plane with charged particles
  class ATLAS_2020_I1790256: public Analysis {
  public:

    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2020_I1790256);


    /// @name Analysis methods
    /// @{

    void init() {

      // Projections
      FinalState fs(Cuts::abseta < 4.5);
      FastJets jet4(fs, JetAlg::ANTIKT, 0.4, JetMuons::NONE, JetInvisibles::NONE);
      declare(jet4, "Jets");

      ChargedFinalState tracks(Cuts::pT > 0.5*GeV && Cuts::abseta < 2.5);
      declare(tracks, "tracks");

      book(_h_lundplane, 1,1,1);

      _h_vs.resize(13);
      for (size_t i = 0; i < _h_vs.size(); ++i) {
        book(_h_vs[i] , i+3 , 1, 1);
      }

      _h_hs.resize(19);
      for (size_t i = 0; i < _h_hs.size(); ++i) {
        book(_h_hs[i], i+16, 1, 1);
      }

      book(_njets, "_njets");
    }


    void analyze(const Event& event) {

      const Jets jets = apply<JetFinder>(event, "Jets").jetsByPt(Cuts::pT > 300*GeV && Cuts::abseta < 2.1);

      if (jets.size() < 2)  vetoEvent;
      if (jets[0].pT() < 675*GeV)  vetoEvent;

      if ( (jets[0].pT()/jets[1].pT()) > 1.5 ) vetoEvent;

       _njets->fill(2);

       const Particles& tracks = apply<ChargedFinalState>(event, "tracks").particlesByPt();

       Particles intracks1;
       Particles intracks2;

       const Jet& j1 = jets[0];
       const Jet& j2 = jets[1];


      for (const Particle& p : tracks) {
        const double dr = deltaR(j1, p, PSEUDORAPIDITY);
        if (dr > 0.4) continue;
          if (abs(p.pid()) == 13) continue;
        intracks1.push_back(p);
      }

      for (const Particle& p : tracks) {
        const double dr = deltaR(j2, p, PSEUDORAPIDITY);
        if (dr > 0.4) continue;
        if (abs(p.pid()) == 13) continue;
        intracks2.push_back(p);
      }

      JetDefinition tjet1_def(fastjet::cambridge_algorithm, 10);
      ClusterSequence tjet1_cs(intracks1, tjet1_def);
      vector<PseudoJet> tjets1 = fastjet::sorted_by_pt(tjet1_cs.inclusive_jets(0.0));

      JetDefinition tjet2_def(fastjet::cambridge_algorithm, 10);
      ClusterSequence tjet2_cs(intracks2, tjet2_def);
      vector<PseudoJet> tjets2 = fastjet::sorted_by_pt(tjet2_cs.inclusive_jets(0.0));

      if (tjets1.size() < 1 || tjets2.size() < 1) vetoEvent;

      fjcontrib::LundGenerator lund;
      vector<fjcontrib::LundDeclustering> declusts1 = lund(tjets1[0]);
      for (size_t idecl = 0; idecl < declusts1.size(); ++idecl) {
        pair<double,double> coords = declusts1[idecl].lund_coordinates();
        double X = -0.9163 + coords.first;
        double Y = - log(declusts1[idecl].z());

        if (X > 0 && X < 4.33 && Y > log(1/0.5)  && Y < 8.6*log(1/0.5) ){

          _h_lundplane->fill(X, Y);

          double hdiv = (double)4.33/(double)13;
          size_t i = floor(X/hdiv);
          _h_vs[i]->fill(Y);

          double vdiv = (8.6*log(1/0.5) - log(1/0.5))/(double)19;
          size_t j = floor((Y - log(1/0.5))/vdiv);
          _h_hs[j]->fill(X);

        }
      }

      vector<fjcontrib::LundDeclustering> declusts2 = lund(tjets2[0]);
      for (size_t idecl = 0; idecl < declusts2.size(); ++idecl) {
        pair<double,double> coords = declusts2[idecl].lund_coordinates();

        double X = -0.9163 + coords.first;
        double Y = - log(declusts2[idecl].z());

        if (X > 0 && X < 4.33 && Y > log(1/0.5)  && Y < 8.6*log(1/0.5) ) {

          _h_lundplane->fill(X, Y);

          double hdiv = (double)4.33/(double)13;
          size_t i = floor(X/hdiv);
          _h_vs[i]->fill(Y);

          double vdiv = (8.6*log(1/0.5) - log(1/0.5))/(double)19;
          size_t j = floor((Y - log(1/0.5))/vdiv);
          _h_hs[j]->fill(X);
        }
      }
    }


    void finalize() {

      double area = _njets->sumW();
      if (area > 0) {
        scale(_h_lundplane, 1/area);
        scale(_h_vs, 1/(area*0.333));
        scale(_h_hs, 1/(area*0.277));
      }

    }


  private:

    Histo2DPtr _h_lundplane;
    vector<Histo1DPtr> _h_vs, _h_hs;
    CounterPtr _njets;

  };



  RIVET_DECLARE_PLUGIN(ATLAS_2020_I1790256);

}

Rivet analyses

Lund jet plane with charged particles

Source code:ATLAS_2020_I1790256.cc

Source code:`ATLAS_2020_I1790256.cc`