Rivet analyses
energy asymmetry in ttj @ 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1941095
Status: VALIDATED
Authors: - Alexander Basan
References: - arXiv: 2110.05453
Beams: p+ p+
Beam energies: (6500.0, 6500.0)GeV
Run details: - semileptonic top-quark pair plus jet production at 13 TeV
A measurement of the energy asymmetry in jet-associated top-quark pair production is presented using 139 fb−1 of data collected by the ATLAS detector at the Large Hadron Collider during pp collisions at $\sqrt{s}=13$ TeV. The observable measures the different probability of top and antitop quarks to have the higher energy as a function of the jet scattering angle with respect to the beam axis. The energy asymmetry is measured in the semileptonic tt̄ decay channel, and the hadronically decaying top quark must have transverse momentum above 350 GeV. The results are corrected for detector effects to particle level in three bins of the scattering angle of the associated jet. The measurement agrees with the SM prediction at next-to-leading-order accuracy in quantum chromodynamics in all three bins. In the bin with the largest expected asymmetry, where the jet is emitted perpendicular to the beam, the energy asymmetry is measured to be −0.043 ± 0.020, in agreement with the SM prediction of −0.037 ± 0.003. Interpreting this result in the framework of the Standard Model effective field theory (SMEFT), it is shown that the energy asymmetry is sensitive to the top-quark chirality in four-quark operators and is therefore a valuable new observable in global SMEFT fits.
Source
code:ATLAS_2021_I1941095.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/InvisibleFinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/MissingMomentum.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/PartonicTops.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Tools/MendelMin.hh"
#include "fastjet/tools/Filter.hh"
namespace Rivet {
/// @brief Energy asymmetry in ttj at 13 TeV
class ATLAS_2021_I1941095 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2021_I1941095);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Declare projections
// Photons
PromptFinalState promptphotons(Cuts::abspid == PID::PHOTON, TauDecaysAs::NONPROMPT);
// Electrons
PromptFinalState bare_el(Cuts::abspid == PID::ELECTRON, TauDecaysAs::PROMPT);
LeptonFinder all_dressed_el(bare_el, promptphotons, 0.1, Cuts::abseta < 2.5);
LeptonFinder electrons(bare_el, promptphotons, 0.1, Cuts::abseta < 2.5 && Cuts::pT > 25*GeV);
declare(electrons,"electrons");
// Muons
PromptFinalState bare_mu(Cuts::abspid == PID::MUON, TauDecaysAs::PROMPT);
LeptonFinder all_dressed_mu(bare_mu, promptphotons, 0.1, Cuts::abseta < 2.5);
LeptonFinder muons(bare_mu, promptphotons, 0.1, Cuts::abseta <2.5 && Cuts::pT > 25*GeV);
declare(muons,"muons");
// AntiKt4TruthWZJets as AntiKt4TruthWZJets, but w/o photons from hadrons in dressing
const InvisibleFinalState invisibles(OnlyPrompt::YES, TauDecaysAs::PROMPT);
VetoedFinalState vfs(FinalState(Cuts::abseta < 5.0)); // changed from 4.5 to 5.0
vfs.addVetoOnThisFinalState(all_dressed_el);
vfs.addVetoOnThisFinalState(all_dressed_mu);
vfs.addVetoOnThisFinalState(invisibles); // new
FastJets jets(vfs, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::ALL); // changed invisible from DECAY to ALL
declare(jets,"jets");
// AntiKt10TruthTrimmedPtFrac5SmallR20Jets
FinalState fs(Cuts::abseta < 5.0);
FastJets fjets(fs, JetAlg::ANTIKT, 1.0, JetMuons::NONE, JetInvisibles::NONE);
_trimmer = fastjet::Filter(fastjet::JetDefinition(fastjet::kt_algorithm, 0.2),
fastjet::SelectorPtFractionMin(0.05));
declare(fjets,"fjets");
// Missing momentum
declare(MissingMomentum(), "MissingMomentum");
// Parton level top quarks after FSR
// options are: decaymode, emu_from_prompt_tau, include_hadronic_taus
declare(PartonicTops(TopDecay::E_MU, PromptEMuFromTau::YES, InclHadronicTau::NO), "PartonicTops_EMU");
declare(PartonicTops(TopDecay::E_MU, PromptEMuFromTau::NO, InclHadronicTau::NO), "PartonicTops_EMU_notau");
declare(PartonicTops(TopDecay::HADRONIC, PromptEMuFromTau::NO, InclHadronicTau::YES), "PartonicTops_HADRONIC");
declare(PartonicTops(TopDecay::HADRONIC, PromptEMuFromTau::NO, InclHadronicTau::NO), "PartonicTops_HADRONIC_notau");
// Book histograms
const Estimate1D& ref_asymm = refData(1, 1, 1);
book(_h["pos"], "_thetaj_opt_depos", ref_asymm.xEdges());
book(_h["neg"], "_thetaj_opt_deneg", ref_asymm.xEdges());
book(_asymm, 1, 1, 1);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// Parton-level top quarks // after FSR
const Particles partonicTops_EMU = apply<ParticleFinder>(event, "PartonicTops_EMU").particlesByPt();
const Particles partonicTops_EMU_notau = apply<ParticleFinder>(event, "PartonicTops_EMU_notau").particlesByPt();
const Particles partonicTops_HADRONIC = apply<ParticleFinder>(event, "PartonicTops_HADRONIC").particlesByPt();
const Particles partonicTops_HADRONIC_notau = apply<ParticleFinder>(event, "PartonicTops_HADRONIC_notau").particlesByPt();
// Filter semi-leptonic (e,mu,tau) events: Veto dileptonic/nonleptonic events and events with 2 taus
int nLeptons = partonicTops_EMU.size() + partonicTops_HADRONIC.size() - partonicTops_HADRONIC_notau.size();
if (nLeptons != 1) vetoEvent;
// Get the selected objects, using the projections.
DressedLeptons electrons = apply<LeptonFinder>(event, "electrons").dressedLeptons();
DressedLeptons muons = apply<LeptonFinder>(event, "muons").dressedLeptons();
const Jets& jets = apply<FastJets>(event, "jets").jetsByPt(Cuts::pT > 25*GeV && Cuts::abseta < 2.5);
const Jets& fjets = apply<FastJets>(event, "fjets").jetsByPt(Cuts::pT > 200*GeV && Cuts::abseta < 2.0);
PseudoJets ljets;
for (const Jet& fjet : fjets) { ljets += _trimmer(fjet); }
sort(ljets.begin(), ljets.end(), [](PseudoJet const &l, PseudoJet const &r) { return l.pt() > r.pt(); });
const FourMomentum& met = apply<MissingMomentum>(event, "MissingMomentum").missingMomentum();
// Overlap removal
for (const Jet& jet : jets) {
idiscard(electrons, deltaRLess(jet, 0.4, RAPIDITY));
idiscard(muons, deltaRLess(jet, 0.4, RAPIDITY));
}
// Reconstruct event
// Lepton l
size_t n_el_25 = 0, n_el_27 = 0;
for (const DressedLepton& electron : electrons ) {
if (electron.pT() >= 25*GeV) ++n_el_25;
if (electron.pT() >= 27*GeV) ++n_el_27;
}
size_t n_mu_25 = 0, n_mu_27 = 0;
for (const DressedLepton& muon : muons ) {
if (muon.pT() >= 25*GeV) ++n_mu_25;
if (muon.pT() >= 27*GeV) ++n_mu_27;
}
if ((n_el_25 + n_mu_25 != 1) || (n_el_27 + n_mu_27 != 1)) vetoEvent;
DressedLepton lepton = (n_el_27 == 1)? electrons[0] : muons[0];
FourMomentum l = lepton.mom();
int lep_charge = lepton.charge();
// Neutrino nu
FourMomentum nu = getNeutrino(l, met);
// Hadronic top candidate jh
int jh_idx = -1;
for (size_t ijet = 0; ijet < ljets.size(); ++ijet) {
Jet ljet = Jet(ljets[ijet]);
if (ljet.pT() < 350*GeV) continue;
if (ljet.abseta() > 2.0) continue;
if (ljet.mass() < 140*GeV) continue;
if (deltaPhi(ljet,l) < 1.0) continue;
bool btagged = false;
for (const Jet& jet : jets) {
if ( jet.bTagged(Cuts::pT > 5*GeV) ) {
if ( deltaR(ljet, jet) < 1.0 ) {
btagged = true;
break;
}
}
}
if (btagged) {
jh_idx = ijet;
break;
}
}
if ( jh_idx == -1 ) vetoEvent;
FourMomentum jh = Jet(ljets[jh_idx]).mom();
// Leptonic top b-jet candidate jl
int jl_idx = -1;
for (size_t ijet = 0; ijet < jets.size(); ++ijet) {
if ( !jets[ijet].bTagged(Cuts::pT > 5*GeV) ) continue;
if ( deltaR(jets[ijet], l) > 2.0 ) continue;
if ( deltaR(jets[ijet], jh) < 1.5 ) continue;
jl_idx = ijet;
break;
}
if ( jl_idx == -1) {
for (size_t ijet = 0; ijet < jets.size(); ++ijet) {
if ( deltaR(jets[ijet], l) > 2.0 ) continue;
if ( deltaR(jets[ijet], jh) < 1.5 ) continue;
jl_idx = ijet;
break;
}
}
if ( jl_idx == -1 ) vetoEvent;
FourMomentum jl = Jet(jets[jl_idx]).mom();
// b-tagging
size_t n_btagged = 0;
size_t n_btagged_matched = 1; // Large-jet jh is b-tagged
for (const Jet& jet : jets ) {
if (jet.bTagged(Cuts::pT > 5*GeV)) ++n_btagged;
}
if ( jets[jl_idx].bTagged(Cuts::pT > 5*GeV) ) ++n_btagged_matched;
if ( n_btagged >= 2 && n_btagged_matched < 2 ) vetoEvent;
// Associated jet candidate ja
int ja_idx = -1;
for (int ijet = 0; ijet < int(jets.size()); ++ijet) {
if ( ijet == jl_idx ) continue;
if ( jets[ijet].pT() < 100*GeV ) continue;
if ( deltaR(jets[ijet], jh) < 1.5 ) continue;
if ( deltaR(jets[ijet], l) < 0.4 ) continue;
ja_idx = ijet;
break;
}
if ( ja_idx == -1 ) vetoEvent;
FourMomentum ja = jets[ja_idx].mom();
FourMomentum thad = jh;
FourMomentum tlep = l+nu+jl;
FourMomentum top = lep_charge > 0 ? tlep : thad;
FourMomentum tbar = lep_charge > 0 ? thad : tlep;
FourMomentum ttbar = top + tbar;
FourMomentum ttj = top + tbar + ja;
// Boost into ttj reference frame
FourMomentum ttj_inv( ttj.E(), -ttj.px(), -ttj.py(), -ttj.pz() );
Vector3 boostVector = ttj_inv.betaVec();
LorentzTransform lt_boost;
lt_boost.setBetaVec( boostVector );
FourMomentum top_boosted = lt_boost.transform( top );
FourMomentum tbar_boosted = lt_boost.transform( tbar );
FourMomentum ja_boosted = lt_boost.transform( ja );
// Get observables
const double deltaE = top_boosted.E() - tbar_boosted.E();
const double thetaj_opt = ttj.rapidity() > 0 ? ja_boosted.theta() : pi - ja_boosted.theta();
// Fill auxiliary histograms
_h[deltaE > 0 ? "pos" : "neg"]->fill(thetaj_opt);
}
/// Normalise histograms etc., after the run
void finalize() {
scale(_h, crossSection()/picobarn/sumW());
// Calculate differential energy asymmetry
asymm(_h["pos"], _h["neg"], _asymm);
}
/// @}
private:
fastjet::Filter _trimmer;
// Histograms
map<string, Histo1DPtr> _h;
Estimate1DPtr _asymm;
static double delta2_fcn(const MendelMin::Params& p, const MendelMin::Params& pfix) {
double delta2 = 0;
double alpha = p[0]*6.30-3.15; // Map p[0] in [0,1] to alpha in [-3.15,3.15]
double r = pfix[0];
double dphi = pfix[1];
double l_pt = pfix[2];
double l_m = pfix[3];
double n_px = pfix[4];
double n_py = pfix[5];
r /= sqrt(l_pt * l_pt + l_m * l_m) - l_pt * cos(dphi + alpha);
FourMomentum neut(0.0, n_px, n_py, 0.0); // E, px, py, pz
neut.setE(neut.p());
FourMomentum neut_new( 0.0, r * neut.p() * cos(neut.phi() + alpha), r * neut.p() * sin(neut.phi() + alpha), 0.0 );
neut_new.setE(neut_new.p());
delta2 = pow((neut_new.px() - neut.px()), 2) + pow((neut_new.py() - neut.py()), 2);
return delta2;
}
FourMomentum getNeutrino(const FourMomentum& lepton, const FourMomentum& met) {
const double m_mWpdg = 80.4*GeV;
double pxNu = met.px();
double pyNu = met.py();
double ptNu = met.pt();
double pzNu;
double c1 = pow(m_mWpdg,2) - pow(lepton.mass(),2) + 2 * (lepton.px() * pxNu + lepton.py() * pyNu);
double b1 = 2 * lepton.pz();
double A = 4*pow(lepton.E(),2) - b1*b1;
double B = -2 * c1 * b1;
double C = 4 * pow(lepton.E(), 2) * ptNu * ptNu - c1 * c1;
double discr = B*B - 4*A*C;
double r = 1;
double sol1, sol2;
if (discr > 0){
sol1 = (-B + sqrt(discr)) / (2*A);
sol2 = (-B - sqrt(discr)) / (2*A);
}
else {
// fitAlpha
std::valarray<double> pfix = { (m_mWpdg * m_mWpdg - lepton.mass() * lepton.mass()) / (2 * ptNu), met.phi() - lepton.phi(),
lepton.pt(), lepton.mass(), pxNu, pyNu };
MendelMin mm(delta2_fcn, 1, pfix);
mm.evolve(100);
valarray<double> fittest = mm.fittest();
const double alpha = fittest[0]*6.30-3.15; // map p[0] in [0,1] to alpha in [-3.15,3.15]
const double dphi = met.phi() - lepton.phi();
r = ( pow(m_mWpdg,2) - pow(lepton.mass(),2) );
r /= (2 * ptNu * (sqrt(pow(lepton.pt(),2) + pow(lepton.mass(),2)) - lepton.pt() * cos(dphi + alpha)));
const double old_p = ptNu;
const double old_phi = met.phi();
pxNu = r * old_p * cos(old_phi + alpha);
pyNu = r * old_p * sin(old_phi + alpha);
ptNu = sqrt (pxNu*pxNu + pyNu*pyNu);
c1 = pow(m_mWpdg,2) - pow(lepton.mass(),2) + 2 * (lepton.px() * pxNu + lepton.py() * pyNu);
B = -2 * c1 * b1;
C = 4 * pow(lepton.E(),2) * ptNu * ptNu - c1 * c1;
discr = B*B - 4*A*C;
sol1 = -B / (2*A);
sol2 = -B / (2*A);
}
// useSmallestPz
pzNu = (fabs(sol1) > fabs(sol2)) ? sol2 : sol1;
FourMomentum nu( sqrt(sqr(pxNu) + sqr(pyNu) + sqr(pzNu)), pxNu, pyNu, pzNu);
return nu;
}
};
RIVET_DECLARE_PLUGIN(ATLAS_2021_I1941095);
}