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## Rivet analyses reference

### ATLAS_2012_I1199269

Inclusive diphoton $+ X$ events at $\sqrt{s} = 7$ TeV
Experiment: ATLAS (LHC)
Inspire ID: 1199269
Status: VALIDATED
Authors:
• Giovanni Marchiori
References:
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
• Inclusive diphoton $+ X$ events at $\sqrt{s} = 7$ TeV.

The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at $\sqrt{s} = 7$ TeV. The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb$^{-1}$, is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter ($|\eta|<1.37$ and $1.52<|\eta|<2.37$) and with an angular separation $\Delta R>0.4$, is $44.0^{+3.2}_{-4.2}$ pb. The differential cross sections as a function of the di-photon invariant mass, transverse momentum, azimuthal separation, and cosine of the polar angle of the largest transverse energy photon in the Collins--Soper di-photon rest frame are also measured. The results are compared to the prediction of leading-order parton-shower and next-to-leading-order and next-to-next-to-leading-order parton-level generators.

Source code: ATLAS_2012_I1199269.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 // -*- C++ -*- #include "Rivet/Analysis.hh" #include "Rivet/Projections/IdentifiedFinalState.hh" #include "Rivet/Projections/FastJets.hh" namespace Rivet { /// @brief Measurement of isolated diphoton + X differential cross-sections /// /// Inclusive isolated gamma gamma cross-sections, differential in M(gg), pT(gg), /// dphi(gg), cos(theta*)_CS /// /// @author Giovanni Marchiori /// class ATLAS_2012_I1199269 : public Analysis { public: /// Constructor ATLAS_2012_I1199269() : Analysis("ATLAS_2012_I1199269") { } /// Book histograms and initialise projections before the run void init() { FinalState fs; declare(fs, "FS"); FastJets fj(fs, FastJets::KT, 0.5); fj.useJetArea(new fastjet::AreaDefinition(fastjet::VoronoiAreaSpec())); declare(fj, "KtJetsD05"); IdentifiedFinalState photonfs(Cuts::abseta < 2.37 && Cuts::pT > 22*GeV); photonfs.acceptId(PID::PHOTON); declare(photonfs, "Photon"); book(_h_M ,1, 1, 1); book(_h_pT ,2, 1, 1); book(_h_dPhi ,3, 1, 1); book(_h_cosThetaStar ,4, 1, 1); } /// Perform the per-event analysis void analyze(const Event& event) { // Require at least 2 photons in final state const Particles photons = apply(event, "Photon").particlesByPt(); if (photons.size() < 2) vetoEvent; // Get jets, and corresponding jet areas vector > ptDensities(_eta_bins_areaoffset.size()-1); const auto clust_seq_area = apply(event, "KtJetsD05").clusterSeqArea(); for (const Jet& jet : apply(event, "KtJetsD05").jets()) { const double area = clust_seq_area->area(jet); // implicit .pseudojet() if (area < 1e-3) continue; const int ieta = binIndex(jet.abseta(), _eta_bins_areaoffset); if (ieta != -1) ptDensities[ieta].push_back(jet.pT()/area); } // Compute median jet properties over the jets in the event vector vptDensity; //, vsigma, vNjets; for (size_t b = 0; b < _eta_bins_areaoffset.size()-1; ++b) { vptDensity += ptDensities[b].empty() ? 0 : median(ptDensities[b]); } // Loop over photons and fill vector of isolated ones Particles isolated_photons; for (const Particle& photon : photons) { /// Remove photons in ECAL crack region if (inRange(photon.abseta(), 1.37, 1.52)) continue; // Compute isolation via particles within an R=0.4 cone of the photon const Particles& fs = apply(event, "FS").particles(); FourMomentum mom_in_EtCone; for (const Particle& p : fs) { // Reject if not in cone if (deltaR(photon, p) > 0.4) continue; // Reject if in the 5x7 cell central core if (fabs(deltaEta(photon, p)) < 0.025 * 5 * 0.5 && fabs(deltaPhi(photon, p)) < PI/128. * 7 * 0.5) continue; // Sum momentum mom_in_EtCone += p.momentum(); } // Now figure out the correction (area*density) const double ETCONE_AREA = PI*sqr(0.4) - (7*.025)*(5*PI/128.); // cone area - central core rectangle const double correction = vptDensity[binIndex(photon.abseta(), _eta_bins_areaoffset)] * ETCONE_AREA; // Discard the photon if there is more than 4 GeV of cone activity // NOTE: Shouldn't need to subtract photon itself (it's in the central core) // NOTE: using expected cut at hadron/particle level, not at reco level if (mom_in_EtCone.Et() - correction > 4*GeV) continue; // Add isolated photon to list isolated_photons.push_back(photon); } // Require at least two isolated photons and select leading pT pair if (isolated_photons.size() < 2) vetoEvent; sortByPt(isolated_photons); const FourMomentum& y1 = isolated_photons[0].momentum(); const FourMomentum& y2 = isolated_photons[1].momentum(); // Leading photon should have pT > 25 GeV if (y1.pT() < 25*GeV) vetoEvent; // Require the two photons to be separated by dR > 0.4 if (deltaR(y1, y2) < 0.4) vetoEvent; // Compute diphoton vector and fill histos FourMomentum yy = y1 + y2; const double costhetayy = 2 * y1.pT() * y2.pT() * sinh(y1.eta() - y2.eta()) / yy.mass() / add_quad(yy.mass(), yy.pT()); _h_M->fill(yy.mass()/GeV); _h_pT->fill(yy.pT()/GeV); _h_dPhi->fill(mapAngle0ToPi(y1.phi() - y2.phi())); _h_cosThetaStar->fill(costhetayy); } /// Normalise histograms etc., after the run void finalize() { scale(_h_M, crossSection()/sumOfWeights()); scale(_h_pT, crossSection()/sumOfWeights()); scale(_h_dPhi, crossSection()/sumOfWeights()); scale(_h_cosThetaStar, crossSection()/sumOfWeights()); } private: Histo1DPtr _h_M, _h_pT, _h_dPhi, _h_cosThetaStar; const vector _eta_bins_areaoffset = {0.0, 1.5, 3.0}; }; DECLARE_RIVET_PLUGIN(ATLAS_2012_I1199269); }