Rivet analyses
Pseudo-top-antitop cross sections
Experiment: ATLAS (LHC)
Inspire ID: 1345452
Status: VALIDATED
Authors: - Longen Lan - Aldo Saavedra - Kevin Finelli
References: - Expt page: ATLAS-TOPQ-2013-07 - arXiv: 1502.05923
Beams: p+ p+
Beam energies: (3500.0, 3500.0)GeV
Run details: - top-antitop production, reconstructed from leptons + jets final state
Various differential cross-sections are measured in top-quark pair (tt̄) events produced in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV at the LHC with the ATLAS detector. These differential cross-sections are presented in a data set corresponding to an integrated luminosity of 4.6 fb−1. The differential cross-sections are presented in terms of kinematic variables of a top-quark proxy referred to as the pseudo-top-quark whose dependence on theoretical models is minimal. The pseudo-top-quark can be defined in terms of either reconstructed detector objects or stable particles in an analogous way. The measurements are performed on tt̄ events in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of them tagged as originating from a b-quark. The hadronic and leptonic pseudo-top-quarks are defined via the leptonic or hadronic decay mode of the W boson produced by the top-quark decay in events with a single charged lepton. The cross-section is measured as a function of the transverse momentum and rapidity of both the hadronic and leptonic pseudo-top-quark as well as the transverse momentum, rapidity and invariant mass of the pseudo-top-quark pair system. The measurements are corrected for detector effects and are presented within a kinematic range that closely matches the detector acceptance.
Source
code:ATLAS_2015_I1345452.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
namespace Rivet {
/// @brief ATLAS 7 TeV pseudo-top analysis
///
/// @author K .Finelli <kevin.finelli@cern.ch>
/// @author A. Saavedra <a.saavedra@physics.usyd.edu.au>
/// @author L. Lan <llan@physics.usyd.edu.au>
class ATLAS_2015_I1345452 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2015_I1345452);
void init() {
// Eta ranges
Cut eta_full = Cuts::abseta < 5.0 && Cuts::pT >= 1.0 * MeV;
Cut eta_lep = Cuts::abseta < 2.5;
// 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
IdentifiedFinalState el_id(fs);
el_id.acceptIdPair(PID::ELECTRON);
PromptFinalState electrons(el_id);
electrons.acceptTauDecays(true);
declare(electrons, "electrons");
LeptonFinder dressedelectrons(electrons, photons, 0.1, eta_lep && Cuts::pT > 25 * GeV);
declare(dressedelectrons, "dressedelectrons");
LeptonFinder ewdressedelectrons(electrons, photons, 0.1, eta_full);
declare(ewdressedelectrons, "ewdressedelectrons");
LeptonFinder vetodressedelectrons(electrons, photons, 0.1, eta_lep && Cuts::pT > 15 * GeV);
declare(vetodressedelectrons, "vetodressedelectrons");
// Projection to find the muons
IdentifiedFinalState mu_id(fs);
mu_id.acceptIdPair(PID::MUON);
PromptFinalState muons(mu_id);
muons.acceptTauDecays(true);
declare(muons, "muons");
LeptonFinder dressedmuons(muons, photons, 0.1, eta_lep && Cuts::pT > 25 * GeV);
declare(dressedmuons, "dressedmuons");
LeptonFinder ewdressedmuons(muons, photons, 0.1, eta_full);
declare(ewdressedmuons, "ewdressedmuons");
LeptonFinder vetodressedmuons(muons, photons, 0.1, eta_lep && Cuts::pT > 15 * GeV);
declare(vetodressedmuons, "vetodressedmuons");
// Projection to find neutrinos and produce MET
IdentifiedFinalState nu_id;
nu_id.acceptNeutrinos();
PromptFinalState neutrinos(nu_id);
neutrinos.acceptTauDecays(true);
declare(neutrinos, "neutrinos");
// Jet clustering.
VetoedFinalState vfs;
vfs.addVetoOnThisFinalState(ewdressedelectrons);
vfs.addVetoOnThisFinalState(ewdressedmuons);
vfs.addVetoOnThisFinalState(neutrinos);
FastJets jets(vfs, JetAlg::ANTIKT, 0.4);
jets.useInvisibles();
declare(jets, "jets");
//pseudotop leptons and hadrons
book(_h["ptpseudotophadron_mu"], 1, 1, 2);
book(_h["ptpseudotophadron_el"], 2, 1, 2);
book(_h["absrappseudotophadron_mu"], 3, 1, 2);
book(_h["absrappseudotophadron_el"], 4, 1, 2);
book(_h["ptpseudotoplepton_mu"], 5, 1, 2);
book(_h["ptpseudotoplepton_el"], 6, 1, 2);
book(_h["absrappseudotoplepton_mu"], 7, 1, 2);
book(_h["absrappseudotoplepton_el"], 8, 1, 2);
book(_h["ptttbar_mu"], 9, 1, 2);
book(_h["ptttbar_el"], 10, 1, 2);
book(_h["absrapttbar_mu"], 11, 1, 2);
book(_h["absrapttbar_el"], 12, 1, 2);
book(_h["ttbarmass_mu"], 13, 1, 2);
book(_h["ttbarmass_el"], 14, 1, 2);
book(_h["ptpseudotophadron"], 15, 1, 2);
book(_h["absrappseudotophadron"], 16, 1, 2);
book(_h["ptpseudotoplepton"], 17, 1, 2);
book(_h["absrappseudotoplepton"], 18, 1, 2);
book(_h["ptttbar"], 19, 1, 2);
book(_h["absrapttbar"], 20, 1, 2);
book(_h["ttbarmass"], 21, 1, 2);
}
void analyze(const Event& event) {
// Get the selected objects, using the projections.
_dressedelectrons = apply<LeptonFinder>(event, "dressedelectrons").dressedLeptons();
_vetodressedelectrons = apply<LeptonFinder>(event, "vetodressedelectrons").dressedLeptons();
_dressedmuons = apply<LeptonFinder>(event, "dressedmuons").dressedLeptons();
_vetodressedmuons = apply<LeptonFinder>(event, "vetodressedmuons").dressedLeptons();
_neutrinos = apply<PromptFinalState>(event, "neutrinos").particlesByPt();
const Jets& all_jets = apply<FastJets>(event, "jets")
.jetsByPt(Cuts::pT > 25.0 * GeV && Cuts::abseta < 2.5);
//get true l+jets events by removing events with more than 1 electron||muon neutrino
unsigned int n_elmu_neutrinos = 0;
for (const Particle& p : _neutrinos) {
if (p.abspid() == 12 || p.abspid() == 14) ++n_elmu_neutrinos;
}
if (n_elmu_neutrinos != 1) vetoEvent;
DressedLepton* lepton;
if (_dressedelectrons.size())
lepton = &_dressedelectrons[0];
else if (_dressedmuons.size())
lepton = &_dressedmuons[0];
else
vetoEvent;
// Calculate the missing ET, using the prompt neutrinos only (really?)
/// @todo Why not use MissingMomentum?
FourMomentum met;
for (const Particle& p : _neutrinos) met += p.momentum();
//remove jets if they are within dR < 0.2 of lepton
Jets jets;
for (const Jet& jet : all_jets) {
bool keep = true;
for (const DressedLepton& el : _vetodressedelectrons) {
keep &= deltaR(jet, el) >= 0.2;
}
if (keep) jets += jet;
}
bool overlap = false;
Jets bjets, lightjets;
for (unsigned int i = 0; i < jets.size(); ++i) {
const Jet& jet = jets[i];
for (const DressedLepton& el : _dressedelectrons) overlap |= deltaR(jet, el) < 0.4;
for (const DressedLepton& mu : _dressedmuons) overlap |= deltaR(jet, mu) < 0.4;
for (unsigned int j = i + 1; j < jets.size(); ++j) {
overlap |= deltaR(jet, jets[j]) < 0.5;
}
//// Count the number of b-tags
bool b_tagged = false; // This is closer to the
Particles bTags = jet.bTags(); // analysis. Something
for (Particle b : bTags) { // about ghost-associated
b_tagged |= b.pT() > 5 * GeV; // B-hadrons
} //
if (b_tagged)
bjets += jet;
else
lightjets += jet;
}
// remove events with object overlap
if (overlap) vetoEvent;
if (bjets.size() < 2 || lightjets.size() < 2) vetoEvent;
FourMomentum pbjet1; //Momentum of bjet1
FourMomentum pbjet2; //Momentum of bjet2
if (deltaR(bjets[0], *lepton) <= deltaR(bjets[1], *lepton)) {
pbjet1 = bjets[0].momentum();
pbjet2 = bjets[1].momentum();
}
else {
pbjet1 = bjets[1].momentum();
pbjet2 = bjets[0].momentum();
}
FourMomentum pjet1; // Momentum of jet1
if (lightjets.size()) pjet1 = lightjets[0].momentum();
FourMomentum pjet2; // Momentum of jet 2
if (lightjets.size() > 1) pjet2 = lightjets[1].momentum();
double pz = computeneutrinoz(lepton->momentum(), met);
FourMomentum ppseudoneutrino(sqrt(sqr(met.px()) + sqr(met.py()) + sqr(pz)), met.px(), met.py(), pz);
//compute leptonic, hadronic, combined pseudo-top
FourMomentum ppseudotoplepton = lepton->momentum() + ppseudoneutrino + pbjet1;
FourMomentum ppseudotophadron = pbjet2 + pjet1 + pjet2;
FourMomentum pttbar = ppseudotoplepton + ppseudotophadron;
// Evaluate basic event selection
bool pass_eljets = (_dressedelectrons.size() == 1) && (_vetodressedelectrons.size() < 2)
&& (_vetodressedmuons.empty()) && (met.pT() > 30 * GeV)
&& (_mT(_dressedelectrons[0].momentum(), met) > 35 * GeV) && (jets.size() >= 4);
bool pass_mujets = (_dressedmuons.size() == 1) && (_vetodressedmuons.size() < 2)
&& (_vetodressedelectrons.empty()) && (met.pT() > 30 * GeV)
&& (_mT(_dressedmuons[0].momentum(), met) > 35 * GeV) && (jets.size() >= 4);
// basic event selection requirements
if (!pass_eljets && !pass_mujets) vetoEvent;
// Fill histograms
//pseudotop hadrons and leptons fill histogram
_h["ptpseudotoplepton"]->fill(ppseudotoplepton.pt()); //pT of pseudo top lepton
_h["absrappseudotoplepton"]->fill(ppseudotoplepton.absrap()); //absolute rapidity of pseudo top lepton
_h["ptpseudotophadron"]->fill(ppseudotophadron.pt()); //pT of pseudo top hadron
_h["absrappseudotophadron"]->fill(ppseudotophadron.absrap()); //absolute rapidity of pseudo top hadron
_h["absrapttbar"]->fill(pttbar.absrap()); //absolute rapidity of ttbar
_h["ttbarmass"]->fill(pttbar.mass()); //mass of ttbar
_h["ptttbar"]->fill(pttbar.pt()); //fill pT of ttbar in combined channel
if (pass_eljets) { // electron channel fill histogram
_h["ptpseudotoplepton_el"]->fill(ppseudotoplepton.pt()); //pT of pseudo top lepton
_h["absrappseudotoplepton_el"]->fill(
ppseudotoplepton.absrap()); //absolute rapidity of pseudo top lepton
_h["ptpseudotophadron_el"]->fill(ppseudotophadron.pt()); //pT of pseudo top hadron
_h["absrappseudotophadron_el"]->fill(
ppseudotophadron.absrap()); //absolute rapidity of pseudo top hadron
_h["absrapttbar_el"]->fill(pttbar.absrap()); //absolute rapidity of ttbar
_h["ttbarmass_el"]->fill(pttbar.mass()); // fill electron channel ttbar mass
_h["ptttbar_el"]->fill(pttbar.pt()); //fill pT of ttbar in electron channel
}
else { // muon channel fill histogram
_h["ptpseudotoplepton_mu"]->fill(ppseudotoplepton.pt()); //pT of pseudo top lepton
_h["absrappseudotoplepton_mu"]->fill(
ppseudotoplepton.absrap()); //absolute rapidity of pseudo top lepton
_h["ptpseudotophadron_mu"]->fill(ppseudotophadron.pt()); //pT of pseudo top hadron
_h["absrappseudotophadron_mu"]->fill(
ppseudotophadron.absrap()); //absolute rapidity of pseudo top hadron
_h["absrapttbar_mu"]->fill(pttbar.absrap()); //absolute rapidity of ttbar
_h["ttbarmass_mu"]->fill(pttbar.mass()); //fill muon channel histograms
_h["ptttbar_mu"]->fill(pttbar.pt()); //fill pT of ttbar in electron channel
}
}
void finalize() {
// Normalize to cross-section
const double scalefactor(crossSection() / picobarn / sumOfWeights());
for (map<string, Histo1DPtr>::iterator hit = _h.begin(); hit != _h.end(); ++hit) {
double sf = scalefactor;
if ((hit->first).find("_") == std::string::npos) sf *= 0.5;
scale(hit->second, sf);
}
}
private:
double computeneutrinoz(const FourMomentum& lepton, FourMomentum& met) const {
//computing z component of neutrino momentum given lepton and met
double pzneutrino;
double m_W = 80.399; // in GeV, given in the paper
double k = ((sqr(m_W) - sqr(lepton.mass())) / 2) + (lepton.px() * met.px() + lepton.py() * met.py());
double a = sqr(lepton.E()) - sqr(lepton.pz());
double b = -2 * k * lepton.pz();
double c = sqr(lepton.E()) * sqr(met.pT()) - sqr(k);
double discriminant = sqr(b) - 4 * a * c;
double quad[2] = {(-b - sqrt(discriminant)) / (2 * a),
(-b + sqrt(discriminant)) / (2 * a)}; //two possible quadratic solns
if (discriminant < 0)
pzneutrino = -b / (2 * a); //if the discriminant is negative
else { //if the discriminant is greater than or equal to zero, take the soln with smallest absolute value
double absquad[2];
for (int n = 0; n < 2; ++n) absquad[n] = fabs(quad[n]);
if (absquad[0] < absquad[1])
pzneutrino = quad[0];
else
pzneutrino = quad[1];
}
if (!std::isfinite(pzneutrino)) std::cout << "Found non-finite value\n";
return pzneutrino;
}
double _mT(const FourMomentum& l, FourMomentum& nu) const {
return sqrt(2 * l.pT() * nu.pT() * (1 - cos(deltaPhi(l, nu))));
}
/// @name Objects that are used by the event selection decisions
DressedLeptons _dressedelectrons, _vetodressedelectrons, _dressedmuons, _vetodressedmuons;
Particles _neutrinos;
map<string, Histo1DPtr> _h;
};
RIVET_DECLARE_PLUGIN(ATLAS_2015_I1345452);
}