Rivet Analyses Reference

ATLAS_2013_I1230812

$Z$ + jets in $pp$ at 7 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1230812
Status: VALIDATED
Authors:
  • Katharina Bierwagen
  • Frank Siegert
References:
  • arXiv: 1304.7098
  • J. High Energy Phys. 07 (2013) 032
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Z+jets, electronic Z-decays (data are a weighted combination of electron/muon).

Measurements of the production of jets of particles in association with a $Z$ boson in $pp$ collisions at $\sqrt{s}$ = 7 TeV are presented, using data corresponding to an integrated luminosity of 4.6/fb collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in $Z$ events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum $p_T > 30$ GeV and rapidity $|y| < 4.4$. This Rivet module implements the event selection for the weighted combination of both decay channels to produce the average cross section for a single lepton flavour, and uses the data from that combination (as in the paper plots). In the default mode this is how it will run, assuming mixed electronic and muonic events. If LMODE is set to EL (MU), the plots for the individual decay channels (with a slightly different fiducial phase space) are made.

Source code: ATLAS_2013_I1230812.cc
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ZFinder.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"

namespace Rivet {


  /// Z + jets in pp at 7 TeV (combined channel / base class)
  /// @note This base class contains a "mode" variable for combined, e, and mu channel derived classes
  class ATLAS_2013_I1230812 : public Analysis {
  public:

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

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2013_I1230812);
    //@}


    /// 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;

      // Determine the e/mu decay channels used (NB Prompt leptons only).
      /// @todo Note that Zs are accepted with any rapidity: the cuts are on the e/mu: is this correct?
      Cut pt20 = Cuts::pT >= 20*GeV;
      Cut eta_e = _mode? Cuts::abseta < 1.37 || Cuts::absetaIn(1.52, 2.47) : Cuts::abseta < 2.5;
      Cut eta_m = _mode? Cuts::abseta < 2.4 : Cuts::abseta < 2.5;
      ZFinder zfinder_el(FinalState(eta_e), pt20, PID::ELECTRON, 66*GeV, 116*GeV);
      ZFinder zfinder_mu(FinalState(eta_m), pt20, PID::MUON, 66*GeV, 116*GeV);
      declare(zfinder_el, "zfinder_el");
      declare(zfinder_mu, "zfinder_mu");

      // Define veto FS in order to prevent Z-decay products entering the jet algorithm
      VetoedFinalState had_fs;
      had_fs.addVetoOnThisFinalState(getProjection<ZFinder>("zfinder_el"));
      had_fs.addVetoOnThisFinalState(getProjection<ZFinder>("zfinder_mu"));
      FastJets jets(had_fs, FastJets::ANTIKT, 0.4, JetAlg::Muons::ALL, JetAlg::Invisibles::ALL);
      declare(jets, "jets");

      book(_h_njet_incl              ,  1, 1, _mode+1);
      book(_h_njet_incl_ratio        ,  2, 1, _mode+1, true);
      book(_h_njet_excl              ,  3, 1, _mode+1);
      book(_h_njet_excl_ratio        ,  4, 1, _mode+1, true);
      book(_h_njet_excl_pt150        ,  5, 1, _mode+1);
      book(_h_njet_excl_pt150_ratio  ,  6, 1, _mode+1, true);
      book(_h_njet_excl_vbf          ,  7, 1, _mode+1);
      book(_h_njet_excl_vbf_ratio    ,  8, 1, _mode+1, true);
      book(_h_ptlead                 ,  9, 1, _mode+1);
      book(_h_ptseclead              , 10, 1, _mode+1);
      book(_h_ptthirdlead            , 11, 1, _mode+1);
      book(_h_ptfourthlead           , 12, 1, _mode+1);
      book(_h_ptlead_excl            , 13, 1, _mode+1);
      book(_h_pt_ratio               , 14, 1, _mode+1);
      book(_h_pt_z                   , 15, 1, _mode+1);
      book(_h_pt_z_excl              , 16, 1, _mode+1);
      book(_h_ylead                  , 17, 1, _mode+1);
      book(_h_yseclead               , 18, 1, _mode+1);
      book(_h_ythirdlead             , 19, 1, _mode+1);
      book(_h_yfourthlead            , 20, 1, _mode+1);
      book(_h_deltay                 , 21, 1, _mode+1);
      book(_h_mass                   , 22, 1, _mode+1);
      book(_h_deltaphi               , 23, 1, _mode+1);
      book(_h_deltaR                 , 24, 1, _mode+1);
      book(_h_ptthirdlead_vbf        , 25, 1, _mode+1);
      book(_h_ythirdlead_vbf         , 26, 1, _mode+1);
      book(_h_ht                     , 27, 1, _mode+1);
      book(_h_st                     , 28, 1, _mode+1);
    }


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

      FourMomentum z, lp, lm;
      const ZFinder& zfinder_el = apply<ZFinder>(event, "zfinder_el");
      const ZFinder& zfinder_mu = apply<ZFinder>(event, "zfinder_mu");

      bool e_ok = zfinder_el.constituents().size() == 2 && zfinder_mu.constituents().size() ==0;
      bool m_ok = zfinder_el.constituents().size() == 0 && zfinder_mu.constituents().size() ==2;

      if (_mode == 0 &&  !e_ok && !m_ok ) vetoEvent;
      if (_mode == 1 && !e_ok) vetoEvent;
      if (_mode == 2 && !m_ok) vetoEvent;

      if (zfinder_el.constituents().size() == 2) {
        z = zfinder_el.boson().momentum();
        lp = zfinder_el.constituents()[0].momentum();
        lm = zfinder_el.constituents()[1].momentum();
      }
      else if (zfinder_mu.constituents().size() == 2) {
        z = zfinder_mu.boson().momentum();
        lp = zfinder_mu.constituents()[0].momentum();
        lm = zfinder_mu.constituents()[1].momentum();
      }
      else  vetoEvent;

      if (deltaR(lp, lm) < 0.2) vetoEvent;

      Jets jets = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 30*GeV && Cuts::absrap < 4.4);
      ifilter_discard(jets, deltaRLess(lp, 0.5));
      ifilter_discard(jets, deltaRLess(lm, 0.5));

      // Fill jet multiplicities
      for (size_t ijet = 0; ijet <= jets.size(); ++ijet) {
        _h_njet_incl->fill(ijet);
      }
      _h_njet_excl->fill(jets.size());

      // Require at least one jet
      if (jets.size() >= 1) {
        // Leading jet histos
        const double ptlead   = jets[0].pT()/GeV;
        const double yabslead = fabs(jets[0].rapidity());
        const double ptz   = z.pT()/GeV;
        _h_ptlead->fill(ptlead);
        _h_ylead ->fill(yabslead);
        _h_pt_z  ->fill(ptz);
        // Fill jet multiplicities
        if (ptlead > 150)  _h_njet_excl_pt150->fill(jets.size());

        // Loop over selected jets, fill inclusive distributions
        double st = 0;
        double ht = lp.pT()/GeV + lm.pT()/GeV;
        for (size_t ijet = 0; ijet < jets.size(); ++ijet) {
          ht += jets[ijet].pT()/GeV;
          st += jets[ijet].pT()/GeV;
        }
        _h_ht->fill(ht);
        _h_st->fill(st);

        // Require exactly one jet
        if (jets.size() == 1) {
          _h_ptlead_excl->fill(ptlead);
          _h_pt_z_excl  ->fill(ptz);
        }
      }


      // Require at least two jets
      if (jets.size() >= 2) {
        // Second jet histos
        const double ptlead      = jets[0].pT()/GeV;
        const double pt2ndlead   = jets[1].pT()/GeV;
        const double ptratio     = pt2ndlead/ptlead;
        const double yabs2ndlead = fabs(jets[1].rapidity());
        _h_ptseclead->fill(pt2ndlead);
        _h_yseclead->fill( yabs2ndlead);
        _h_pt_ratio->fill( ptratio);

        // Dijet histos
        const double deltaphi = fabs(deltaPhi(jets[1], jets[0]));
        const double deltarap = fabs(jets[0].rapidity() - jets[1].rapidity()) ;
        const double deltar   = fabs(deltaR(jets[0], jets[1], RAPIDITY));
        const double mass     = (jets[0].momentum() + jets[1].momentum()).mass()/GeV;
        _h_mass->fill(    mass);
        _h_deltay->fill(  deltarap);
        _h_deltaphi->fill(deltaphi);
        _h_deltaR->fill(  deltar);

        if (mass > 350 && deltarap > 3)  _h_njet_excl_vbf->fill(jets.size());
      }

      // Require at least three jets
      if (jets.size() >= 3) {
        // Third jet histos
        const double pt3rdlead   = jets[2].pT()/GeV;
        const double yabs3rdlead = fabs(jets[2].rapidity());
        _h_ptthirdlead->fill(pt3rdlead);
        _h_ythirdlead->fill( yabs3rdlead);

        //Histos after VBF preselection
        const double deltarap = fabs(jets[0].rapidity() - jets[1].rapidity()) ;
        const double mass     = (jets[0].momentum() + jets[1].momentum()).mass();
        if (mass > 350 && deltarap > 3) {
          _h_ptthirdlead_vbf->fill(pt3rdlead);
          _h_ythirdlead_vbf->fill( yabs3rdlead);
        }
      }

      // Require at least four jets
      if (jets.size() >= 4) {
        // Fourth jet histos
        const double pt4thlead   = jets[3].pT()/GeV;
        const double yabs4thlead = fabs(jets[3].rapidity());
        _h_ptfourthlead->fill(pt4thlead);
        _h_yfourthlead->fill( yabs4thlead);
      }
    }

    /// @name Ratio calculator util functions
    //@{

    /// Calculate the efficiency error, being careful about div-by-zero
    double err_incl(const HistoBin1D &M, const HistoBin1D &N, bool hasWeights) {
      double r = safediv(M.sumW(), N.sumW());
      if (hasWeights) { // use F. James's approximation for weighted events
        return sqrt( safediv((1 - 2 * r) * M.sumW2() + r * r * N.sumW2(), N.sumW() * N.sumW()) );
      }
      return sqrt( safediv(r * (1 - r), N.sumW()) );
    }

    /// Calculate the ratio error, being careful about div-by-zero
    double err_excl(const HistoBin1D &A, const HistoBin1D &B) {
      double r = safediv(A.sumW(), B.sumW());
      double dAsquared = safediv(A.sumW2(), A.sumW() * A.sumW()); // squared relative error of A
      double dBsquared = safediv(B.sumW2(), B.sumW() * B.sumW()); // squared relative error of B
      return r * sqrt(dAsquared + dBsquared);
    }

    //@}


    void finalize() {
      bool hasWeights = _h_njet_incl->effNumEntries() != _h_njet_incl->numEntries();
      for (size_t i = 0; i < 6; ++i) {
        _h_njet_incl_ratio->point(i).setY(safediv(_h_njet_incl->bin(i + 1).sumW(), _h_njet_incl->bin(i).sumW()),
                                          err_incl(_h_njet_incl->bin(i + 1), _h_njet_incl->bin(i), hasWeights));
        _h_njet_excl_ratio->point(i).setY(safediv(_h_njet_excl->bin(i + 1).sumW(), _h_njet_excl->bin(i).sumW()),
                                          err_excl(_h_njet_excl->bin(i + 1), _h_njet_excl->bin(i)));
        if (i >= 1) {
          _h_njet_excl_pt150_ratio->point(i - 1).setY(safediv(_h_njet_excl_pt150->bin(i).sumW(), _h_njet_excl_pt150->bin(i - 1).sumW()),
                                                      err_excl(_h_njet_excl_pt150->bin(i), _h_njet_excl_pt150->bin(i - 1)));
          if (i >= 2) {
            _h_njet_excl_vbf_ratio->point(i - 2).setY(safediv(_h_njet_excl_vbf->bin(i).sumW(), _h_njet_excl_vbf->bin(i - 1).sumW()),
                                                      err_excl(_h_njet_excl_vbf->bin(i), _h_njet_excl_vbf->bin(i - 1)));
          }
        }
      }

      double sf = _mode? 1.0 : 0.5;
      const double xs = sf * crossSectionPerEvent()/picobarn;

      scale(_h_njet_incl, xs); scale(_h_njet_excl, xs); scale(_h_njet_excl_pt150, xs); 
      scale(_h_njet_excl_vbf, xs); scale(_h_ptlead, xs); scale(_h_ptseclead, xs); 
      scale(_h_ptthirdlead, xs); scale(_h_ptfourthlead, xs); scale(_h_ptlead_excl, xs);
      scale(_h_pt_ratio, xs); scale(_h_pt_z, xs); scale(_h_pt_z_excl, xs);
      scale(_h_ylead, xs); scale(_h_yseclead, xs); scale(_h_ythirdlead, xs); 
      scale(_h_yfourthlead, xs); scale(_h_deltay, xs); scale(_h_mass, xs); 
      scale(_h_deltaphi, xs); scale(_h_deltaR, xs); scale(_h_ptthirdlead_vbf, xs); 
      scale(_h_ythirdlead_vbf, xs); scale(_h_ht, xs); scale(_h_st, xs);
    }

    //@}


  protected:

    size_t _mode;


  private:

    Scatter2DPtr _h_njet_incl_ratio;
    Scatter2DPtr _h_njet_excl_ratio;
    Scatter2DPtr _h_njet_excl_pt150_ratio;
    Scatter2DPtr _h_njet_excl_vbf_ratio;
    Histo1DPtr _h_njet_incl;
    Histo1DPtr _h_njet_excl;
    Histo1DPtr _h_njet_excl_pt150;
    Histo1DPtr _h_njet_excl_vbf;
    Histo1DPtr _h_ptlead;
    Histo1DPtr _h_ptseclead;
    Histo1DPtr _h_ptthirdlead;
    Histo1DPtr _h_ptfourthlead;
    Histo1DPtr _h_ptlead_excl;
    Histo1DPtr _h_pt_ratio;
    Histo1DPtr _h_pt_z;
    Histo1DPtr _h_pt_z_excl;
    Histo1DPtr _h_ylead;
    Histo1DPtr _h_yseclead;
    Histo1DPtr _h_ythirdlead;
    Histo1DPtr _h_yfourthlead;
    Histo1DPtr _h_deltay;
    Histo1DPtr _h_mass;
    Histo1DPtr _h_deltaphi;
    Histo1DPtr _h_deltaR;
    Histo1DPtr _h_ptthirdlead_vbf;
    Histo1DPtr _h_ythirdlead_vbf;
    Histo1DPtr _h_ht;
    Histo1DPtr _h_st;
  };


  RIVET_DECLARE_PLUGIN(ATLAS_2013_I1230812);

}