Rivet analyses
title: ATLAS_2017_I1645627
Isolated photon + jets at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1645627
Status: VALIDATED
Authors: - Ana Rosario Cueto Gomez - Christian Gutschow
References: - Expt page: ATLAS-STDM-2017-01 - Phys.Lett. B780 (2018) 578-602 - DOI: 10.1016/j.physletb.2 - arXiv: 1801.00112
Beams: p+ p+
Beam energies: (6500.0, 6500.0)GeV
Run details: - prompt photon + jets
The dynamics of isolated-photon production in association with a jet in proton-proton collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset with an integrated luminosity of 3.2 fb$^{-1}$. Photons are required to have transverse energies above 125 GeV. Jets are identified using the anti-$k_\text{t}$ algorithm with radius parameter $R=0.4$ and required to have transverse momenta above 100 GeV. Measurements of isolated-photon plus jet cross sections are presented as functions of the leading-photon transverse energy, the leading-jet transverse momentum, the azimuthal angular separation between the photon and the jet, the photon-jet invariant mass and the scattering angle in the photon-jet centre-of-mass system. Tree-level plus parton-shower predictions from Sherpa and Pythia as well as next-to-leading-order QCD predictions from Jetphox and Sherpa are compared to the measurements.
Source code:ATLAS_2017_I1645627.cc
```c++ // -- C++ --
include "Rivet/Analysis.hh"
include "Rivet/Projections/FastJets.hh"
include "Rivet/Projections/FinalState.hh"
include "Rivet/Projections/PromptFinalState.hh"
include "Rivet/Projections/VetoedFinalState.hh"
include "Rivet/Projections/VisibleFinalState.hh"
namespace Rivet {
/// @brief Isolated photon + jets at 13 TeV class ATLAS_2017_I1645627 : public Analysis { public:
// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2017_I1645627);
// Book histograms and initialise projections before the run
void init() {
const FinalState fs;
// calorimeter particles
VisibleFinalState visFS(fs);
VetoedFinalState calo_fs(visFS);
calo_fs.addVetoPairId(PID::MUON);
declare(calo_fs, "calo");
// Voronoi eta-phi tessellation with KT jets, for ambient energy density calculation
FastJets fj(fs, JetAlg::KT, 0.5, JetMuons::NONE, JetInvisibles::NONE); // E-scheme used by default;
fj.useJetArea(new fastjet::AreaDefinition(fastjet::voronoi_area, fastjet::VoronoiAreaSpec(1.0)));
declare(fj, "KtJetsD05");
// photon
PromptFinalState photonfs(Cuts::abspid == PID::PHOTON && Cuts::abseta < 2.37 && Cuts::pT > 125 * GeV);
declare(photonfs, "photons");
// Jets
FastJets jetpro(fs, JetAlg::ANTIKT, 0.4, JetMuons::NONE, JetInvisibles::NONE);
declare(jetpro, "Jets");
// Histograms
book(_h_photon_pt, 1, 1, 1);
book(_h_jet_pt, 2, 1, 1);
book(_h_phjet_dphi, 3, 1, 1);
book(_h_phjet_mass, 4, 1, 1);
book(_h_phjet_costheta, 5, 1, 1);
}
size_t getEtaBin(double eta) const {
return binIndex(fabs(eta), _eta_bins_areaoffset);
}
// Perform the per-event analysis
void analyze(const Event& event) {
// Get the photon
const Particles& photons = apply<PromptFinalState>(event, "photons")
.particlesByPt(Cuts::abseta < 1.37 || Cuts::abseta > 1.56);
if (photons.empty()) vetoEvent;
const FourMomentum photon = photons[0].momentum();
// Get the jet
Jets jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 100 * GeV && Cuts::absrap < 2.37);
idiscard(jets, deltaRLess(photon, 0.8));
if (jets.empty()) vetoEvent;
FourMomentum leadingJet = jets[0].momentum();
// Compute the jet pT densities
vector<vector<double>> ptDensities(_eta_bins_areaoffset.size() - 1);
FastJets fastjets = apply<FastJets>(event, "KtJetsD05");
const auto clust_seq_area = fastjets.clusterSeqArea();
for (const Jet& jet : fastjets.jets()) {
const double area = clust_seq_area->area(jet); // Implicit call to pseudojet().
//const double area2 = (clust_seq_area->area_4vector(jet)).perp(); // Area definition used in egammaTruthParticles.
if (area > 1e-3 && jet.abseta() < _eta_bins_areaoffset.back()) {
ptDensities.at(getEtaBin(jet.abseta())) += jet.pT() / area;
}
}
// Compute the median event energy density
vector<double> ptDensity;
for (size_t b = 0; b < _eta_bins_areaoffset.size() - 1; ++b) {
ptDensity += ptDensities[b].empty() ? 0 : median(ptDensities[b]);
}
// Compute photon isolation with a standard ET cone
FourMomentum mom_in_EtCone;
const Particles calo_fs = apply<VetoedFinalState>(event, "calo").particles();
const double iso_dr = 0.4;
for (const Particle& p : calo_fs) {
// Check if it's in the cone of .4
if (sqrt(2.0 * (cosh(p.eta() - photon.eta()) - cos(p.phi() - photon.phi()))) >= iso_dr) continue;
// Increment sum
mom_in_EtCone += p.momentum();
}
// Remove the photon energy from the isolation
mom_in_EtCone -= photon;
// Figure out the correction (area*density)
const double etcone_area = PI * iso_dr * iso_dr;
const double correction = ptDensity[getEtaBin(photon.abseta())] * etcone_area;
// Require photon to be isolated
if ((mom_in_EtCone.Et() - correction) > (0.0042 * photon.pT() + 10 * GeV)) vetoEvent;
// Fill histos
const double photon_pt = photon.pT() / GeV;
const double jet_pt = leadingJet.pT() / GeV;
const double phjet_dphi = deltaPhi(photon, leadingJet);
const double photon_eta = photon.eta();
const double jet_y = leadingJet.rapidity();
_h_photon_pt->fill(photon_pt);
_h_jet_pt->fill(jet_pt);
_h_phjet_dphi->fill(phjet_dphi);
double dy = fabs(jet_y - photon_eta);
double phjet_costheta = tanh(dy / 2.);
double phjet_mass = (photon + leadingJet).mass() / GeV;
if (phjet_mass <= 450.) vetoEvent;
if (fabs(photon_eta + jet_y) >= 2.37) vetoEvent;
if (phjet_costheta >= 0.83) vetoEvent;
_h_phjet_costheta->fill(phjet_costheta);
_h_phjet_mass->fill(phjet_mass);
}
/// Normalise histograms etc., after the run
void finalize() {
const double sf = crossSection() / picobarn / sumOfWeights();
scale(_h_photon_pt, sf);
scale(_h_jet_pt, sf);
scale(_h_phjet_dphi, sf);
scale(_h_phjet_mass, sf);
scale(_h_phjet_costheta, sf);
}
private:
Histo1DPtr _h_photon_pt, _h_jet_pt;
Histo1DPtr _h_phjet_dphi, _h_phjet_mass, _h_phjet_costheta;
const vector<double> _eta_bins_areaoffset = {0.0, 1.5, 3.0, 4.0, 5.0};
};
RIVET_DECLARE_PLUGIN(ATLAS_2017_I1645627);
} ```