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ATLAS_2019_I1740909

Jet fragmentation using charged particles
Experiment: ATLAS (LHC)
Inspire ID: 1740909
Status: VALIDATED
Authors:
  • Ben Nachman
  • Deepak Kar
References:
  • arXiv: 1906.09254
  • Phys.Rev.D 100 (2019) 5, 052011
Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • p + p -> jj

This paper presents a measurement of quantities related to the formation of jets from high-energy quarks and gluons (fragmentation). Jets with transverse momentum 100 GeV $< p_T <$ 2.5 TeV and pseudorapidity $|\eta|<2.1$ from an integrated luminosity of 33 fb$^{−1}$ of $\sqrt{s}=$13 TeV proton-proton collisions are reconstructed with the ATLAS detector at the Large Hadron Collider. Charged-particle tracks with $p_T >$ 500 MeV and $|\eta|<2.5$ are used to probe the detailed structure of the jet. The fragmentation properties of the more forward and the more central of the two leading jets from each event are studied. The data are unfolded to correct for detector resolution and acceptance effects. Comparisons with parton shower Monte Carlo generators indicate that existing models provide a reasonable description of the data across a wide range of phase space, but there are also significant differences. Furthermore, the data are interpreted in the context of quark- and gluon-initiated jets by exploiting the rapidity dependence of the jet flavor fraction. A first measurement of the charged-particle multiplicity using model-independent jet labels (topic modeling) provides a promising alternative to traditional quark and gluon extractions using input from simulation. The simulations provide a reasonable description of the quark-like data across the jet $p_T$ range presented in this measurement, but the gluon-like data have systematically fewer charged particles than the simulations.

Source code: ATLAS_2019_I1740909.cc
  1#include "Rivet/Analysis.hh"
  2#include "Rivet/Projections/FinalState.hh"
  3#include "Rivet/Projections/VetoedFinalState.hh"
  4#include "Rivet/Projections/InvisibleFinalState.hh"
  5#include "Rivet/Projections/PromptFinalState.hh"
  6#include "Rivet/Projections/FastJets.hh"
  7
  8namespace Rivet {
  9
 10  /// @brief jet fragmentation at 13 TeV
 11  class ATLAS_2019_I1740909: public Analysis {
 12  public:
 13
 14    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1740909);
 15    
 16    /// Book cuts and projections
 17    void init() {
 18
 19      const FinalState bare_MU(Cuts::abspid == PID::MUON);
 20
 21      VetoedFinalState jetinput;
 22      jetinput.addVetoOnThisFinalState(bare_MU);
 23      jetinput.addVetoOnThisFinalState(InvisibleFinalState());
 24
 25      FastJets jetpro(jetinput, FastJets::ANTIKT, 0.4);
 26      declare(jetpro, "Jets");
 27
 28      book(_p["nch_jetpt_F"] , 1, 1, 1);
 29      book(_p["nch_jetpt_C"] , 2, 1, 1);
 30      book(_p["nch_jetpt_B"] , 9, 1, 1);
 31    
 32      for (size_t i_bin = 0; i_bin < 14; ++i_bin) {
 33        book(_h["nch_B"+to_str(i_bin)] , 13 + i_bin, 1, 1); 
 34        book(_hr["r_B"+to_str(i_bin)] , 27 + i_bin, 1, 1); 
 35        book(_h["zeta_B"+to_str(i_bin)] , 41 + i_bin, 1, 1); 
 36        book(_h["pTrel_B"+to_str(i_bin)] , 55 + i_bin, 1, 1); 
 37        book(_h["nch_F"+to_str(i_bin)] , 69 + i_bin, 1, 1); 
 38        book(_hr["r_F"+to_str(i_bin)] , 83 + i_bin, 1, 1); 
 39        book(_h["zeta_F"+to_str(i_bin)] , 97 + i_bin, 1, 1); 
 40        book(_h["pTrel_F"+to_str(i_bin)] , 111 + i_bin, 1, 1);  
 41        book(_h["nch_C"+to_str(i_bin)] , 125 + i_bin, 1, 1); 
 42        book(_hr["r_C"+to_str(i_bin)] , 139 + i_bin, 1, 1); 
 43        book(_h["zeta_C"+to_str(i_bin)] , 153 + i_bin, 1, 1); 
 44        book(_h["pTrel_C"+to_str(i_bin)] , 167 + i_bin, 1, 1);          
 45        }
 46    }
 47
 48    void analyze(const Event& event) {
 49    
 50      //Init
 51      double fnch=0;
 52      double cnch=0;
 53      double fzval=0;
 54      double czval=0;
 55      double frval=0;
 56      double crval=0;
 57      double ftval=0;
 58      double ctval=0;
 59
 60      // Event selection 
 61      Jets m_goodJets = apply<JetAlg>(event, "Jets").jetsByPt(Cuts::pT > 100*GeV && Cuts::abseta < 2.1);
 62      if (m_goodJets.size() < 2) vetoEvent;
 63      if (fabs(1.0 - m_goodJets[0].pT()/m_goodJets[1].pT()) > 0.5)  vetoEvent;
 64      // Decide forward or central   
 65      bool check = m_goodJets[0].abseta() < m_goodJets[1].abseta();
 66      int pos_f = int(check);
 67      int pos_c = int(!check);
 68      
 69      // Calculate obs, separately for central and fwd, also get bin
 70      double fpt = m_goodJets[pos_f].pT();
 71      size_t f_bin = GetJetBin(fpt);
 72      double cpt = m_goodJets[pos_c].pT();
 73      size_t c_bin = GetJetBin(cpt);
 74
 75      for (const Particle& p : m_goodJets[pos_f].particles()) {
 76        if (p.pT() < 0.5*GeV)  continue;
 77        if (p.charge() != 0) {
 78          ++fnch;
 79	                
 80          fzval = p.pT() / m_goodJets[pos_f].pt();        
 81          ftval = p.pT()*sin(p.phi()-m_goodJets[pos_f].phi());                
 82          frval = deltaR(m_goodJets[pos_f], p);
 83               
 84          _hr["r_F"+to_str(f_bin)]->fill(frval);
 85          _hr["r_B"+to_str(f_bin)]->fill(frval);                               
 86          _h["zeta_F"+to_str(f_bin)]->fill(fzval);
 87          _h["zeta_B"+to_str(f_bin)]->fill(fzval);     
 88          _h["pTrel_F"+to_str(f_bin)]->fill(ftval);
 89          _h["pTrel_B"+to_str(f_bin)]->fill(ftval);
 90        }    
 91      }
 92	               
 93	               
 94	    for (const Particle& p : m_goodJets[pos_c].particles()) {            
 95        if (p.pT() < 0.5*GeV)  continue;
 96        if (p.charge() != 0) {
 97          ++cnch;
 98          czval = p.pT() / m_goodJets[pos_c].pt();
 99          ctval = p.pT()*sin(p.phi()-m_goodJets[pos_c].phi());
100          crval = deltaR(m_goodJets[pos_c], p);
101                       
102          _hr["r_C"+to_str(c_bin)]->fill(crval);
103          _hr["r_B"+to_str(c_bin)]->fill(crval);
104          _h["zeta_C"+to_str(c_bin)]->fill(czval);
105          _h["zeta_B"+to_str(c_bin)]->fill(czval);
106          _h["pTrel_C"+to_str(c_bin)]->fill(ctval);
107          _h["pTrel_B"+to_str(c_bin)]->fill(ctval);
108        }
109      }
110
111      if (fnch > 63)  fnch = 63;
112      if (cnch > 63)  cnch = 63;
113       
114       //Fill nchg histo
115       
116      _p["nch_jetpt_F"]->fill(fpt,fnch);
117      _p["nch_jetpt_C"]->fill(cpt,cnch);
118      _p["nch_jetpt_B"]->fill(fpt,fnch);
119      _p["nch_jetpt_B"]->fill(cpt,cnch);
120            
121      _h["nch_F"+to_str(f_bin)]->fill(fnch);
122      _h["nch_C"+to_str(c_bin)]->fill(cnch);
123      _h["nch_B"+to_str(f_bin)]->fill(fnch);
124      _h["nch_B"+to_str(c_bin)]->fill(cnch);
125    }
126 
127    
128    void finalize() {
129    
130      // For r only
131      /// @todo Replace with barchart()
132      for (auto& hist : _hr) {
133        for(size_t i=0; i < hist.second->numBins(); ++i) {
134          double x = hist.second->bin(i).xMid();
135          double bW = hist.second->bin(i).xWidth();
136          hist.second->bin(i).scaleW(bW/(2.0*M_PI*x)); 
137        }  
138      }
139
140      // The rest
141      /// @todo Replace with barchart()
142      for (auto& hist : _h) {                
143        for (size_t i=0; i < hist.second->numBins(); ++i) {
144          double bW = hist.second->bin(i).xWidth();
145          hist.second->bin(i).scaleW(bW); 
146        }
147      }
148                          
149      for (size_t i_bin = 0; i_bin < 14; ++i_bin) {
150      
151        double sfB =  _h["nch_B"+to_str(i_bin)]->sumW();                         
152        if (sfB) {
153          scale(_h["zeta_B"+to_str(i_bin)],2.0/sfB);
154          scale(_h["pTrel_B"+to_str(i_bin)],2.0/sfB);
155          scale(_hr["r_B"+to_str(i_bin)],2.0/sfB);                      
156          scale(_h["nch_B"+to_str(i_bin)], 2.0/sfB);
157        }
158        
159        double sfF =  _h["nch_F"+to_str(i_bin)]->sumW();                         
160        if (sfF) {
161          scale(_h["zeta_F"+to_str(i_bin)],1.0/sfF);
162          scale(_h["pTrel_F"+to_str(i_bin)],1.0/sfF);
163          scale(_hr["r_F"+to_str(i_bin)],1.0/sfF);                      
164          scale(_h["nch_F"+to_str(i_bin)], 1.0/sfF);
165        }
166        
167        double sfC =  _h["nch_C"+to_str(i_bin)]->sumW();                         
168        if (sfC) {
169          scale(_h["zeta_C"+to_str(i_bin)],1.0/sfC);
170          scale(_h["pTrel_C"+to_str(i_bin)],1.0/sfC);
171          scale(_hr["r_C"+to_str(i_bin)],1.0/sfC);                      
172          scale(_h["nch_C"+to_str(i_bin)], 1.0/sfC);                 
173        }
174      }
175    }
176
177  private:
178    
179    size_t GetJetBin(const double jetpt){
180      size_t i_bin = 0;
181      if (inRange(jetpt,100,200)) i_bin=0;
182      if (inRange(jetpt,200,300)) i_bin=1;
183      if (inRange(jetpt,300,400)) i_bin=2;
184      if (inRange(jetpt,400,500)) i_bin=3;
185      if (inRange(jetpt,500,600)) i_bin=4;
186      if (inRange(jetpt,600,700)) i_bin=5;
187      if (inRange(jetpt,700,800)) i_bin=6;
188      if (inRange(jetpt,800,900)) i_bin=7;
189      if (inRange(jetpt,900,1000)) i_bin=8;
190      if (inRange(jetpt,1000,1200)) i_bin=9;
191      if (inRange(jetpt,1200,1400)) i_bin=10;
192      if (inRange(jetpt,1400,1600)) i_bin=11;
193      if (inRange(jetpt,1600,2000)) i_bin=12;
194      if (inRange(jetpt,2000,2500)) i_bin=13;   
195      if(jetpt < 100) i_bin=0;
196      if(jetpt > 2500) i_bin=13; 
197      return i_bin;
198    } 
199  
200    map<string, Histo1DPtr> _h;
201    map<string, Histo1DPtr> _hr;
202    map<string, Profile1DPtr> _p; 
203  };
204  
205  // The hook for the plugin system
206  RIVET_DECLARE_PLUGIN(ATLAS_2019_I1740909);
207  
208}