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ATLAS_2014_I1307243

Measurements of jet vetoes and azimuthal decorrelations in dijet events produced in pp collisions at $\sqrt{s}$ = 7 TeV using the ATLAS detector
Experiment: ATLAS (LHC)
Inspire ID: 1307243
Status: VALIDATED
Authors:
  • James Robinson
References: Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • pp -> jet jet x. sqrt(s) = 7000 GeV. Jets with pT > 60, 50 GeV

Additional jet activity in dijet events is measured using $pp$ collisions at ATLAS at a centre-of-mass energy of 7 TeV, for jets reconstructed using the anti-kt algorithm with radius parameter R=0.6. This is done using variables such as the fraction of dijet events without an additional jet in the rapidity interval bounded by the dijet subsystem and correlations between the azimuthal angles of the dijets. They are presented, both with and without a veto on additional jet activity in the rapidity interval, as a function of the mean transverse momentum of the dijets and of the rapidity interval size. The double differential dijet cross section is also measured as a function of the interval size and the azimuthal angle between the dijets. These variables probe differences in the approach to resummation of large logarithms when performing QCD calculations. The data are compared to POWHEG, interfaced to the PYTHIA 8 and HERWIG parton shower generators, as well as to HEJ with and without interfacing it to the ARIADNE parton shower generator. None of the theoretical predictions agree with the data across the full phase-space considered; however, POWHEG+PYTHIA 8 and HEJ+ARIADNE are found to provide the best agreement with the data. These measurements use the full data sample collected with the ATLAS detector in 7 TeV $pp$ collisions at the LHC and correspond to integrated luminosities of 36.1 pb$^-1$ and 4.5 fb$^-1$ for data collected during 2010 and 2011 respectively.

Source code: ATLAS_2014_I1307243.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Tools/Logging.hh"
  4#include "Rivet/Projections/FastJets.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief ATLAS azimuthal decorrelation with jet veto analysis
 10  /// @author James Robinson <james.robinson@cern.ch>
 11  class ATLAS_2014_I1307243 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2014_I1307243);
 16
 17
 18    /// Book histograms and initialise projections before the run
 19    void init() {
 20
 21      _dy_max = 8; _years = { 2010, 2011 };
 22      _Qnoughts = { 20., 30., 40., 50., 60., 70., 80., 90., 100. };
 23      /// Initialise and register projections here
 24      FastJets fastJets(FinalState(), JetAlg::ANTIKT, 0.6, JetMuons::ALL, JetInvisibles::ALL);
 25      declare(fastJets, "AntiKt6JetsWithInvisibles");
 26
 27
 28      /// Book histograms
 29      for (const string cat : { "inclusive", "gap" }) {
 30        const size_t offset = (cat == "gap") ? 1 : 0;
 31
 32        // Temporary inclusive and gap histograms
 33        book(_aux_dy[cat], "_" + cat + "_dy", refData(1, 1, 1));
 34        book(_aux_pTbar[cat], "_" + cat + "_pTbar", refData(2, 1, 1));
 35
 36        book(_h_C2C1_dy[cat],    7 + 4 * offset, 1, 1);
 37        book(_h_C2C1_pTbar[cat], 8 + 4 * offset, 1, 1);
 38
 39        // Azimuthal moment histograms
 40        book(_p_cosDeltaPhi_dy[cat],        5 + 4 * offset, 1, 1);
 41        book(_p_cosDeltaPhi_pTbar[cat],     6 + 4 * offset, 1, 1);
 42        book(_p_cosTwoDeltaPhi_dy[cat],    37 + 2 * offset, 1, 1);
 43        book(_p_cosTwoDeltaPhi_pTbar[cat], 38 + 2 * offset, 1, 1);
 44
 45        // Gap fraction vs. Q0 and cross-section in dy slices
 46        _s_gapFrac_Q0.resize(_dy_max);
 47        const vector<double> edges {0., 1., 2., 3., 4., 5., 6., 7., 8.};
 48        book(_aux_Q0_dySlices[cat], edges);
 49        book(_h_dphi_dySlices[cat], edges);
 50        for (size_t i=0; i < _aux_Q0_dySlices[cat]->numBins(); ++i) {
 51          const string hname("_" + cat + "_dySlice_" + toString(i) + "_" + toString(i+1) + "_Q0");
 52          book(_aux_Q0_dySlices[cat]->bin(i+1), hname, refData(29+i, 1, 1));
 53          book(_h_dphi_dySlices[cat]->bin(i+1), 13+(_dy_max*offset)+i, 1, 1);
 54          if (!offset)  book(_s_gapFrac_Q0[i], 29 + i, 1, 1); // only book once
 55        }
 56      }
 57
 58      // Number of jets in rapidity interval
 59      book(_s_gapFrac_dy,     1, 1, 1);
 60      book(_s_gapFrac_pTbar,  2, 1, 1);
 61      book(_p_nGapJets_dy,    3, 1, 1);
 62      book(_p_nGapJets_pTbar, 4, 1, 1);
 63    }
 64
 65
 66    /// Perform the per-event analysis
 67    void analyze(const Event& event) {
 68
 69      for (size_t reg = 0; reg < 2; ++reg) {
 70
 71        // Retrieve all anti-kt R=0.6 jets
 72        const double maxRap = reg? 2.4 : 4.4;
 73        const Jets& akt6Jets = apply<JetFinder>(event, "AntiKt6JetsWithInvisibles").jetsByPt(Cuts::absrap < maxRap);
 74        // If there are fewer than 2 jets then bail
 75        if ( akt6Jets.size() < 2 ) { vetoEvent; }
 76
 77        // Require jets to be above {60, 50} GeV
 78        if ( akt6Jets[0].pT() < 60*GeV || akt6Jets[1].pT() < 50*GeV ) { vetoEvent; }
 79
 80        // Identify gap boundaries
 81        const double yMin = std::min(akt6Jets[0].rap(), akt6Jets[1].rap());
 82        const double yMax = std::max(akt6Jets[0].rap(), akt6Jets[1].rap());
 83
 84        // Determine azimuthal decorrelation quantities
 85        const double dy = yMax - yMin;
 86        const double dphi = mapAngle0ToPi(deltaPhi(akt6Jets[0], akt6Jets[1]));
 87        const double pTbar = 0.5*(akt6Jets[0].pT() + akt6Jets[1].pT())/GeV;
 88
 89        // Impose minimum dy for the 2011 phase space
 90        if ( _years[reg] == 2011 && dy < 1.0 ) { vetoEvent; }
 91
 92        // Determine gap quantities
 93        size_t nGapJets = 0;
 94        double maxGapQ0 = 0.;
 95        const double vetoScale = reg? 30*GeV : 20*GeV;
 96        for (const Jet& jet : akt6Jets) {
 97          if (!inRange(jet.rap(), yMin, yMax, OPEN, OPEN))  continue;
 98          const double pT = jet.pT()/GeV;
 99          if (pT > vetoScale) { ++nGapJets; }
100          if (pT > maxGapQ0) { maxGapQ0 = pT; }
101        }
102
103        // Fill histograms
104        fillHists(_years[reg], nGapJets, { dy, pTbar, dphi, maxGapQ0 });
105      }
106      return;
107    }
108
109    void fillHists(const size_t region, const size_t nGapJets, const vector<double>& vars) {
110      assert(vars.size() == 4);
111      const double dy = vars[0];
112      const double pTbar = vars[1];
113      const double dphi = vars[2];
114      const double maxGapQ0 = vars[3];
115      // Determine gap category
116      vector<string> categories = {"inclusive"};
117      if (!nGapJets) { categories += string("gap"); }
118
119      // Fill histograms relevant for comparison with 2010 data
120      if (region == _years[0]) {
121        // Fill inclusive and gap histograms
122        for (const string& cat : categories) {
123          _aux_dy[cat]->fill(dy);
124          _h_dphi_dySlices[cat]->fill(dy, dphi/M_PI);
125          _p_cosDeltaPhi_dy[cat]->fill(dy, cos(M_PI - dphi));
126          _p_cosTwoDeltaPhi_dy[cat]->fill(dy, cos(2*dphi));
127        }
128        // Fill profiled nGapJets
129        _p_nGapJets_dy->fill(dy, nGapJets);
130        // Fill Q0 histograms - can fill multiple points per event
131        for (const double Q0 :  _Qnoughts) {
132          _aux_Q0_dySlices["inclusive"]->fill(dy, Q0);
133          if (maxGapQ0 <= Q0) { _aux_Q0_dySlices["gap"]->fill(dy, Q0); }
134        }
135
136      // Fill histograms relevant for comparison with 2011 data
137      }
138      else if (region == _years[1]) {
139        // Fill inclusive and gap histograms
140        for (const string& cat : categories) {
141          _aux_pTbar[cat]->fill(pTbar);
142          _p_cosDeltaPhi_pTbar[cat]->fill(pTbar, cos(M_PI - dphi));
143          _p_cosTwoDeltaPhi_pTbar[cat]->fill(pTbar, cos(2*dphi));
144        }
145        // Fill profiled nGapJets
146        _p_nGapJets_pTbar->fill(pTbar, nGapJets);
147      }
148      return;
149    }
150
151    /// Normalise histograms etc., after the run
152    void finalize() {
153      // Normalise cross-section plots to correct cross-section
154      const double ySpan = 1.0; // all dy spans are 1
155      const double sf = crossSection() / picobarn / sumOfWeights();
156      for (const string cat : { "inclusive", "gap" }) {
157        scale(_h_dphi_dySlices[cat], sf/ySpan/M_PI);
158        // Create C2/C1 scatter from profiles
159        divide(_p_cosTwoDeltaPhi_dy[cat],    _p_cosDeltaPhi_dy[cat],    _h_C2C1_dy[cat]);
160        divide(_p_cosTwoDeltaPhi_pTbar[cat], _p_cosDeltaPhi_pTbar[cat], _h_C2C1_pTbar[cat]);
161      }
162
163      // Fill simple gap fractions
164      efficiency(_aux_dy["gap"], _aux_dy["inclusive"], _s_gapFrac_dy);
165      efficiency(_aux_pTbar["gap"], _aux_pTbar["inclusive"], _s_gapFrac_pTbar);
166
167      // Register and fill Q0 gap fractions
168      for (size_t dyLow = 0; dyLow < _dy_max; ++dyLow) {
169        efficiency(_aux_Q0_dySlices["gap"]->bin(dyLow+1), _aux_Q0_dySlices["inclusive"]->bin(dyLow+1), _s_gapFrac_Q0[dyLow]);
170      }
171    }
172
173
174  private:
175
176    /// Member variables
177    vector<size_t> _years;
178    vector<double> _Qnoughts;
179
180    size_t _dy_max;
181
182    /// auxiliary histograms for gap fractions
183    map<string, Histo1DPtr> _aux_dy;
184    map<string, Histo1DPtr> _aux_pTbar;
185    map<string, Histo1DGroupPtr> _aux_Q0_dySlices;
186
187    // Gap fractions
188    Estimate1DPtr _s_gapFrac_dy, _s_gapFrac_pTbar;
189    vector<Estimate1DPtr> _s_gapFrac_Q0;
190
191    // Number of jets in rapidity interval
192    Profile1DPtr _p_nGapJets_dy;
193    Profile1DPtr _p_nGapJets_pTbar;
194
195    // Azimuthal moment histograms
196    map<string, Profile1DPtr> _p_cosDeltaPhi_dy;
197    map<string, Profile1DPtr> _p_cosDeltaPhi_pTbar;
198    map<string, Profile1DPtr> _p_cosTwoDeltaPhi_dy;
199    map<string, Profile1DPtr> _p_cosTwoDeltaPhi_pTbar;
200    map<string, Estimate1DPtr> _h_C2C1_dy;
201    map<string, Estimate1DPtr> _h_C2C1_pTbar;
202
203    // Cross-section vs. deltaPhi in deltaY slices
204    map<string, Histo1DGroupPtr> _h_dphi_dySlices;
205  };
206
207  RIVET_DECLARE_PLUGIN(ATLAS_2014_I1307243);
208
209}