Rivet analyses
All-hadronic boosted ttbar at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1646686
Status: VALIDATED
Authors: - Kyle Cormier - Christian Gutschow
References: - Expt page: ATLAS-TOPQ-2016-09 - DOI: 10.17182/hepdata.81709.v1 - arXiv: 1801.02052
Beams: p+ p+
Beam energies: (6500.0, 6500.0)GeV
Run details: - p + p -> ttbar (all-hadronic, boosted)
Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and tt̄ system kinematic observables using proton–proton collisions at a center-of-mass energy of $\sqrt{s}=13$ TeV. The data set corresponds to an integrated luminosity of 36.1 fb−1, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum pT>500 GeV and a second with pT > 350 GeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a b-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated χ2 values. The cross-section for tt̄ production in the fiducial phase-space region is 292$7(stat)76(syst)fb, tobecomparedtothetheoreticalpredictionof384$36 fb.
Source
code:ATLAS_2018_I1646686.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/PartonicTops.hh"
#include "Rivet/Math/LorentzTrans.hh"
#include "Rivet/Tools/Random.hh"
namespace Rivet {
/// @brief All-hadronic ttbar at 13 TeV
class ATLAS_2018_I1646686 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2018_I1646686);
/// Book histograms and initialise projections before the run
void init() {
// Get options particle-level only.
_mode = 0;
if ( getOption("TMODE") == "PARTICLE" ) _mode = 0;
if ( getOption("TMODE") == "BOTH" ) _mode = 1;
//histogram booking
book(_h["inclusive"],1,1,1);
bookHistograms("t_pt", 0, true);
bookHistograms("t_y", 1, true);
bookHistograms("t1_pt", 2);
bookHistograms("t1_y", 3);
bookHistograms("t2_pt", 4);
bookHistograms("t2_y", 5);
bookHistograms("tt_m", 6);
bookHistograms("tt_pt", 7);
bookHistograms("tt_y", 8);
bookHistograms("tt_chi", 9);
bookHistograms("tt_yboost", 10);
bookHistograms("tt_pout", 11);
bookHistograms("tt_dPhi", 12);
bookHistograms("tt_Ht", 13);
bookHistograms("tt_cosThStar", 14);
// Projections
Cut dressed_lep = (Cuts::abseta < 2.5) && (Cuts::pT >= 25*GeV);
Cut eta_full = (Cuts::abseta < 5.0);
// All final state particles
FinalState fs(eta_full);
// Get photons to dress leptons
IdentifiedFinalState photons(fs);
photons.acceptIdPair(PID::PHOTON);
// Projection to find the electrons
PromptFinalState electrons(Cuts::abspid == PID::ELECTRON, TauDecaysAs::PROMPT);
LeptonFinder dressedelectrons(electrons, photons, 0.1, dressed_lep);
declare(dressedelectrons, "elecs");
LeptonFinder ewdressedelectrons(electrons, photons, 0.1, eta_full);
// Projection to find the muons
PromptFinalState muons(Cuts::abspid == PID::MUON, TauDecaysAs::PROMPT);
LeptonFinder dressedmuons(muons, photons, 0.1, dressed_lep);
declare(dressedmuons, "muons");
LeptonFinder ewdressedmuons(muons, photons, 0.1, eta_full);
// Jet clustering.
VetoedFinalState vfs;
vfs.addVetoOnThisFinalState(ewdressedelectrons);
vfs.addVetoOnThisFinalState(ewdressedmuons);
FastJets jets(vfs, JetAlg::ANTIKT, 0.4, JetMuons::DECAY, JetInvisibles::DECAY);
declare(jets, "jets");
FastJets ljets(fs, JetAlg::ANTIKT, 1.0, JetMuons::NONE, JetInvisibles::NONE);
ljets.addTrf(new fastjet::Filter(fastjet::JetDefinition(fastjet::kt_algorithm, 0.2), fastjet::SelectorPtFractionMin(0.05)));
declare(ljets, "ljets" );
if (_mode != 0 ){
PartonicTops partonTops;
declare(partonTops, "partonicTops");
}
}
void analyze(const Event& event) {
if (_mode != 0){
// Parton-level top quarks
const Particles partonicTops = apply<PartonicTops>( event, "partonicTops").particlesByPt();
FourMomentum top, tbar;
bool foundT = false, foundTBar = false;
for (const Particle& ptop : partonicTops) {
const int pid = ptop.pid();
if (pid == PID::TQUARK) {
top = ptop.momentum();
foundT = true;
} else if (pid == -PID::TQUARK) {
tbar = ptop.momentum();
foundTBar = true;
}
}
FourMomentum t1_parton, t2_parton, ttbar_parton;
if ( foundT && foundTBar ) {
t1_parton = top.pT2() > tbar.pT2() ? top : tbar;
t2_parton = top.pT2() > tbar.pT2() ? tbar : top;
ttbar_parton = t1_parton + t2_parton;
if ( t1_parton.pT() > 500*GeV && t2_parton.pT() > 350*GeV) {
const double chi_parton = calcChi(t1_parton, t2_parton);
const double cosThetaStar_parton = abs(calcCosThetaStar(t1_parton, t2_parton));
if (cosThetaStar_parton == -99) {
MSG_DEBUG("ttbar going faster than light! Vetoing event. Try turning of partonic tops?");
vetoEvent;
}
const double pout_parton = abs(calcPout(t1_parton, t2_parton));
const double dPhi_parton = deltaPhi(t1_parton, t2_parton);
const int randomChoice = int(rand01() < 0.5);
const FourMomentum& randomTopParton = (randomChoice == 0) ? t1_parton : t2_parton;
fillParton("t_pt", randomTopParton.pT()/GeV);
fillParton("t_y", randomTopParton.absrap());
fillParton("t1_pt", t1_parton.pT()/GeV);
fillParton("t1_y", t1_parton.absrap());
fillParton("t2_pt", t2_parton.pT()/GeV);
fillParton("t2_y", t2_parton.absrap());
fillParton("tt_m", ttbar_parton.mass()/TeV);
fillParton("tt_pt", ttbar_parton.pT()/GeV);
fillParton("tt_Ht", (t1_parton.pT() + t2_parton.pT())/GeV);
fillParton("tt_y", ttbar_parton.absrap());
fillParton("tt_yboost", 0.5 * abs(t1_parton.rapidity() + t2_parton.rapidity()));
fillParton("tt_chi", chi_parton);
fillParton("tt_cosThStar", cosThetaStar_parton);
fillParton("tt_pout", pout_parton/GeV);
fillParton("tt_dPhi", dPhi_parton);
}
}
}
// Get and veto on dressed leptons
const DressedLeptons dressedElectrons = apply<LeptonFinder>(event, "elecs").dressedLeptons();
const DressedLeptons dressedMuons = apply<LeptonFinder>(event, "muons").dressedLeptons();
if (!dressedElectrons.empty()) vetoEvent;
if (!dressedMuons.empty()) vetoEvent;
// Get jets
const Jets& all_jets = apply<FastJets>( event, "jets").jetsByPt(Cuts::pT > 25*GeV && Cuts::abseta < 2.5);
const FastJets& ljets_fj = apply<FastJets>( event, "ljets");
const Jets trimmedJets = ljets_fj.jetsByPt();
// Check large-R jets
Jets ljets;
vector<bool> b_tagged;
for (const Jet& jet : trimmedJets) {
if (jet.pT() < 250 * GeV) continue;
if (jet.pT() > 3000 * GeV) continue;
if (jet.mass() > jet.pT()) continue;
if (jet.abseta() > 2.0 ) continue;
ljets += jet;
b_tagged += jet.bTagged();
}
if (all_jets.size() < 2) vetoEvent;
if (ljets.size() < 2) vetoEvent;
// Identify top and anti top, compute some event variables
const FourMomentum ttbar = ljets[0].momentum() + ljets[1].momentum();
const FourMomentum t1 = ljets[0].momentum();
const FourMomentum t2 = ljets[1].momentum();
const double chi = calcChi(t1, t2);
const double cosThetaStar = abs(calcCosThetaStar(t1, t2));
if (cosThetaStar == -99) {
MSG_DEBUG("real ttbar going faster than light! This should not happen. Vetoing event.");
vetoEvent;
}
const double pout = abs(calcPout(t1, t2));
const double dPhi = deltaPhi(t1, t2);
if ( t2.pT() < 350*GeV) vetoEvent;
if ( t1.pT() < 500*GeV) vetoEvent;
// b-tagging for particle done on large-R jets
if (!(b_tagged[0] && b_tagged[1])) vetoEvent;
// Continues with signal region cuts
if ( abs(t1.mass() - 172.5 * GeV) > 50*GeV ) vetoEvent;
if ( abs(t2.mass() - 172.5 * GeV) > 50*GeV ) vetoEvent;
_h["inclusive"]->fill(0);
fillHistograms("t1_pt", t1.pT()/GeV);
fillHistograms("t1_y", t1.absrap());
fillHistograms("t2_pt", t2.pT()/GeV);
fillHistograms("t2_y", t2.absrap());
fillHistograms("tt_m", ttbar.mass()/TeV);
fillHistograms("tt_pt", ttbar.pT()/GeV);
fillHistograms("tt_Ht", (t1.pT() + t2.pT())/GeV);
fillHistograms("tt_y", ttbar.absrap());
fillHistograms("tt_yboost", 0.5 * abs(t1.rapidity() + t2.rapidity()));
fillHistograms("tt_chi", chi);
fillHistograms("tt_cosThStar", cosThetaStar);
fillHistograms("tt_pout", pout/GeV);
fillHistograms("tt_dPhi", dPhi);
}
void finalize() {
// Normalize histograms
const double sf = crossSection()/picobarn / sumOfWeights();
for (auto &hist : _h) {
scale(hist.second, sf);
if ((hist.first.find("_norm") != string::npos) && hist.second->integral(false)>0) hist.second->normalize(1.0, false);
}
}
double calcChi(const FourMomentum& t1, const FourMomentum& t2) {
double ystar = 0.5 * (t1.rapidity()-t2.rapidity());
double chi = exp( 2 * abs(ystar));
return chi;
}
double calcCosThetaStar(const FourMomentum& t1, const FourMomentum& t2) {
FourMomentum ttbar = t1 + t2;
LorentzTransform centreOfMassTrans;
ttbar.setX(0);
ttbar.setY(0);
if (ttbar.betaVec().mod2() > 1) return -99;
centreOfMassTrans.setBetaVec( -ttbar.betaVec() );
FourMomentum t1_star = centreOfMassTrans.transform(t1);
double cosThetaStar;
if (t1_star.p3().mod2() >= 0){
cosThetaStar = t1_star.pz()/t1_star.p3().mod();
} else {
return -99;
}
return cosThetaStar;
}
double calcPout(const FourMomentum& t1, const FourMomentum& t2) {
Vector3 t1V = t1.p3();
Vector3 t2V = t2.p3();
Vector3 zUnit = Vector3(0., 0., 1.);
Vector3 vPerp = zUnit.cross(t1V);
double pout = vPerp.dot(t2V)/vPerp.mod();
return pout;
}
protected:
size_t _mode;
private:
map<string, Histo1DPtr> _h;
//some functions for booking, filling and scaling the histograms
void fillHistograms(std::string name, double value) {
_h[name]->fill(value);
_h[name + "_norm"]->fill(value);
}
void fillParton(std::string name, double value) {
_h[name + "_parton"]->fill(value);
_h[name + "_parton_norm"]->fill(value);
}
void bookHistograms(const std::string name, unsigned int index, bool onlyParton = false) {
if (!onlyParton) {
book(_h[name], index, 1, 1 );
book(_h[name + "_norm"], index + 13, 1, 1 );
}
if (_mode != 0) {
book(_h[name + "_parton"], index + 82, 1, 1 );
book(_h[name + "_parton_norm"], index + 97, 1, 1 );
}
}
};
RIVET_DECLARE_PLUGIN(ATLAS_2018_I1646686);
}