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D0_2008_S7719523

Isolated $\gamma$ + jet cross-sections, differential in pT($\gamma$) for various $y$ bins
Experiment: D0 (Tevatron Run 2)
Inspire ID: 782968
Status: VALIDATED
Authors:
  • Andy Buckley
  • Gavin Hesketh
  • Frank Siegert
References: Beams: p- p+
Beam energies: (980.0, 980.0) GeV
Run details:
  • Produce only gamma + jet ($q,\bar{q},g$) hard processes (for Pythia 6, this means MSEL=10 and MSUB indices 14, 29 & 115 enabled). The lowest bin edge is at 30 GeV, so a kinematic pTmin cut is probably required to fill the histograms.

The process $p \bar{p}$ -> photon + jet + X as studied by the D0 detector at the Fermilab Tevatron collider at center-of-mass energy $\sqrt{s} = 1.96 \text{TeV}$. Photons are reconstructed in the central rapidity region $|y_\gamma| < 1.0$ with transverse momenta in the range 30--400 GeV, while jets are reconstructed in either the central $|y_\text{jet}| < 0.8$ or forward $1.5 < |y_\text{jet}| < 2.5$ rapidity intervals with $p_\perp^\text{jet} > 15 \text{GeV}$. The differential cross section $\mathrm{d}^3 \sigma / \mathrm{d}{p_\perp^\gamma} \mathrm{d}{y_\gamma} \mathrm{d}{y_\text{jet}}$ is measured as a function of $p_\perp^\gamma$ in four regions, differing by the relative orientations of the photon and the jet. MC predictions have trouble with simultaneously describing the measured normalization and $p_\perp^\gamma$ dependence of the cross section in any of the four measured regions.

Source code: D0_2008_S7719523.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/LeadingParticlesFinalState.hh"
  5#include "Rivet/Projections/VetoedFinalState.hh"
  6#include "Rivet/Projections/FastJets.hh"
  7
  8namespace Rivet {
  9
 10
 11  /// @brief Measurement of isolated gamma + jet + X differential cross-sections
 12  ///
 13  /// Inclusive isolated gamma + jet cross-sections, differential in pT(gamma), for
 14  /// various photon and jet rapidity bins.
 15  ///
 16  /// @author Andy Buckley
 17  /// @author Gavin Hesketh
 18  class D0_2008_S7719523 : public Analysis {
 19  public:
 20
 21    RIVET_DEFAULT_ANALYSIS_CTOR(D0_2008_S7719523);
 22
 23
 24    /// @name Analysis methods
 25    /// @{
 26
 27    /// Set up projections and book histograms
 28    void init() {
 29      // General FS
 30      FinalState fs;
 31      declare(fs, "FS");
 32
 33      // Get leading photon
 34      LeadingParticlesFinalState photonfs(FinalState((Cuts::etaIn(-1.0, 1.0) && Cuts::pT >=  30.0*GeV)));
 35      photonfs.addParticleId(PID::PHOTON);
 36      declare(photonfs, "LeadingPhoton");
 37
 38      // FS excluding the leading photon
 39      VetoedFinalState vfs(fs);
 40      vfs.addVetoOnThisFinalState(photonfs);
 41      declare(vfs, "JetFS");
 42
 43      // Jets
 44      FastJets jetpro(vfs, FastJets::D0ILCONE, 0.7);
 45      declare(jetpro, "Jets");
 46
 47      // Histograms
 48      book(_h_central_same_cross_section ,1, 1, 1);
 49      book(_h_central_opp_cross_section  ,2, 1, 1);
 50      book(_h_forward_same_cross_section ,3, 1, 1);
 51      book(_h_forward_opp_cross_section  ,4, 1, 1);
 52
 53      // Ratio histos to be filled by divide()
 54      book(_h_cen_opp_same, 5, 1, 1);
 55      book(_h_fwd_opp_same, 8, 1, 1);
 56      // Ratio histos to be filled manually, since the num/denom inputs don't match
 57      book(_h_cen_same_fwd_same, 6, 1, 1, true);
 58      book(_h_cen_opp_fwd_same, 7, 1, 1, true);
 59      book(_h_cen_same_fwd_opp, 9, 1, 1, true);
 60      book(_h_cen_opp_fwd_opp, 10, 1, 1, true);
 61    }
 62
 63
 64
 65    /// Do the analysis
 66    void analyze(const Event& event) {
 67      // Get the photon
 68      const FinalState& photonfs = apply<FinalState>(event, "LeadingPhoton");
 69      if (photonfs.particles().size() != 1) {
 70        vetoEvent;
 71      }
 72      const FourMomentum photon = photonfs.particles().front().momentum();
 73
 74      // Isolate photon by ensuring that a 0.4 cone around it contains less than 7% of the photon's energy
 75      double egamma = photon.E();
 76      double eta_P = photon.eta();
 77      double phi_P = photon.phi();
 78      double econe = 0.0;
 79      for (const Particle& p : apply<FinalState>(event, "JetFS").particles()) {
 80        if (deltaR(eta_P, phi_P, p.eta(), p.phi()) < 0.4) {
 81          econe += p.E();
 82          // Veto as soon as E_cone gets larger
 83          if (econe/egamma > 0.07) {
 84            MSG_DEBUG("Vetoing event because photon is insufficiently isolated");
 85            vetoEvent;
 86          }
 87        }
 88      }
 89
 90      Jets jets = apply<FastJets>(event, "Jets").jetsByPt(15.0*GeV);
 91      if (jets.empty()) vetoEvent;
 92
 93      FourMomentum leadingJet = jets[0].momentum();
 94      if (deltaR(eta_P, phi_P, leadingJet.eta(), leadingJet.phi()) < 0.7) {
 95        vetoEvent;
 96      }
 97
 98      int photon_jet_sign = sign( leadingJet.rapidity() * photon.rapidity() );
 99
100      // Veto if leading jet is outside plotted rapidity regions
101      const double abs_y1 = fabs(leadingJet.rapidity());
102      if (inRange(abs_y1, 0.8, 1.5) || abs_y1 > 2.5) {
103        MSG_DEBUG("Leading jet falls outside acceptance range; |y1| = " << abs_y1);
104        vetoEvent;
105      }
106
107      // Fill histos
108      if (fabs(leadingJet.rapidity()) < 0.8) {
109        Histo1DPtr h = (photon_jet_sign >= 1) ? _h_central_same_cross_section : _h_central_opp_cross_section;
110        h->fill(photon.pT());
111      } else if (inRange( fabs(leadingJet.rapidity()), 1.5, 2.5)) {
112        Histo1DPtr h = (photon_jet_sign >= 1) ? _h_forward_same_cross_section : _h_forward_opp_cross_section;
113        h->fill(photon.pT());
114      }
115
116    }
117
118
119    /// Finalize
120    void finalize() {
121      const double lumi_gen = sumOfWeights()/crossSection();
122      const double dy_photon = 2.0;
123      const double dy_jet_central = 1.6;
124      const double dy_jet_forward = 2.0;
125
126      // Cross-section ratios (6 plots)
127      // Central/central and forward/forward ratios
128      divide(_h_central_opp_cross_section, _h_central_same_cross_section, _h_cen_opp_same);
129      divide(_h_forward_opp_cross_section, _h_forward_same_cross_section, _h_fwd_opp_same);
130      // Central/forward ratio combinations
131      /// @note The central/forward histo binnings are not the same! Hence the need to do these by hand :-(
132      for (size_t i = 0; i < _h_cen_same_fwd_same->numPoints(); ++i) {
133        const YODA::HistoBin1D& cen_same_bini = _h_central_same_cross_section->bin(i);
134        const YODA::HistoBin1D& cen_opp_bini = _h_central_opp_cross_section->bin(i);
135        const YODA::HistoBin1D& fwd_same_bini = _h_central_same_cross_section->bin(i);
136        const YODA::HistoBin1D& fwd_opp_bini = _h_central_opp_cross_section->bin(i);
137        _h_cen_same_fwd_same->point(i).setY(_safediv(cen_same_bini.sumW(), fwd_same_bini.sumW(), 0),
138                                            add_quad(cen_same_bini.relErr(), fwd_same_bini.relErr()));
139        _h_cen_opp_fwd_same->point(i).setY(_safediv(cen_opp_bini.sumW(), fwd_same_bini.sumW(), 0),
140                                           add_quad(cen_opp_bini.relErr(), fwd_same_bini.relErr()));
141        _h_cen_same_fwd_opp->point(i).setY(_safediv(cen_same_bini.sumW(), fwd_opp_bini.sumW(), 0),
142                                           add_quad(cen_same_bini.relErr(), fwd_opp_bini.relErr()));
143        _h_cen_opp_fwd_opp->point(i).setY(_safediv(cen_opp_bini.sumW(), fwd_opp_bini.sumW(), 0),
144                                          add_quad(cen_opp_bini.relErr(), fwd_opp_bini.relErr()));
145      }
146
147      // Use generator cross section for remaining histograms
148      // Each of these needs the additional factor 2 because the
149      // y_photon * y_jet requirement reduces the corresponding 2D "bin width"
150      // by a factor 1/2.
151      scale(_h_central_same_cross_section, 2.0/lumi_gen * 1.0/dy_photon * 1.0/dy_jet_central);
152      scale(_h_central_opp_cross_section, 2.0/lumi_gen * 1.0/dy_photon * 1.0/dy_jet_central);
153      scale(_h_forward_same_cross_section, 2.0/lumi_gen * 1.0/dy_photon * 1.0/dy_jet_forward);
154      scale(_h_forward_opp_cross_section, 2.0/lumi_gen * 1.0/dy_photon * 1.0/dy_jet_forward);
155    }
156
157    /// @}
158
159
160  private:
161
162    // A local scope function for division, handling the div-by-zero case
163    /// @todo Why isn't the math divide() function being found?
164    double _safediv(double a, double b, double result_if_err) {
165      return (b != 0) ? a/b : result_if_err;
166    }
167
168    /// @name Histograms
169    /// @{
170    Histo1DPtr _h_central_same_cross_section;
171    Histo1DPtr _h_central_opp_cross_section;
172    Histo1DPtr _h_forward_same_cross_section;
173    Histo1DPtr _h_forward_opp_cross_section;
174
175    Scatter2DPtr _h_cen_opp_same;
176    Scatter2DPtr _h_fwd_opp_same;
177    Scatter2DPtr _h_cen_same_fwd_same;
178    Scatter2DPtr _h_cen_opp_fwd_same;
179    Scatter2DPtr _h_cen_same_fwd_opp;
180    Scatter2DPtr _h_cen_opp_fwd_opp;
181    /// @}
182
183  };
184
185
186
187  RIVET_DECLARE_ALIASED_PLUGIN(D0_2008_S7719523, D0_2008_I782968);
188
189}