Rivet analyses
Differential cross-sections for Z + b-jets
Experiment: ATLAS (LHC)
Inspire ID: 1788444
Status: VALIDATED
Authors: - Federico Sforza - Deepak Kar
References: - Expt page: ATLAS-STDM-2017-38 - arXiv: 2003.11960
Beams: p+ p+
Beam energies: (6500.0, 6500.0)GeV
Run details: - Z+jets at 13 TeV
This paper presents a measurement of the production cross-section of a Z boson in association with b-jets, in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 35.6 fb−1. Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one or at least two b-jets with transverse momentum pT > 20 GeV and rapidity |y| < 2.5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet. N.B.: Data correspond to average of electron and muon channel. Use LMODE=EL,MU to run on individual channels.
Source
code:ATLAS_2020_I1788444.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DileptonFinder.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/HeavyHadrons.hh"
#include "Rivet/Projections/PromptFinalState.hh"
namespace Rivet {
/// @brief Z + b(b) in pp at 13 TeV
class ATLAS_2020_I1788444 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2020_I1788444);
/// Book histograms and initialise projections before the run
void init() {
_mode = 0;
if ( getOption("LMODE") == "EL" ) _mode = 1;
if ( getOption("LMODE") == "MU" ) _mode = 2;
// Define fiducial cuts for the leptons in the DileptonFinder
Cut lepcuts = (Cuts::pT > 27*GeV) & (Cuts::abseta < 2.5);
DileptonFinder zfinderE(91.2*GeV, 0.1, lepcuts && Cuts::abspid == PID::ELECTRON, Cuts::massIn(76*GeV, 106*GeV));
DileptonFinder zfinderM(91.2*GeV, 0.1, lepcuts && Cuts::abspid == PID::MUON, Cuts::massIn(76*GeV, 106*GeV));
declare(zfinderE, "zfinderE");
declare(zfinderM, "zfinderM");
declare(HeavyHadrons(), "HFHadrons");
// Photons
FinalState photons(Cuts::abspid == PID::PHOTON);
// Muons
PromptFinalState bare_mu(Cuts::abspid == PID::MUON, TauDecaysAs::PROMPT);
LeptonFinder all_dressed_mu(bare_mu, photons, 0.1, Cuts::abseta < 2.5);
// Electrons
PromptFinalState bare_el(Cuts::abspid == PID::ELECTRON, TauDecaysAs::PROMPT);
LeptonFinder all_dressed_el(bare_el, photons, 0.1, Cuts::abseta < 2.5);
//Jet forming
VetoedFinalState vfs(FinalState(Cuts::abseta < 4.5));
vfs.addVetoOnThisFinalState(all_dressed_el);
vfs.addVetoOnThisFinalState(all_dressed_mu);
FastJets jets(vfs, JetAlg::ANTIKT, 0.4, JetMuons::ALL, JetInvisibles::DECAY);
declare(jets, "jets");
// Book histos - binning taken from data.yoda
book(_h["i1b_ZpT"],2,1,1);
book(_h["i1b_ZY"],4,1,1);
book(_h["i1b_dPhiZb"],6,1,1);
book(_h["i1b_dRZb"],8,1,1);
book(_h["i1b_dYZb"],7,1,1);
book(_h["i1b_bpT"],3,1,1);
book(_h["i1b_bY"],5,1,1);
book(_h["i2b_ZpT"],13,1,1);
book(_h["i2b_dPhibb"],9,1,1);
book(_h["i2b_dRbb"],11,1,1);
book(_h["i2b_dYbb"],10,1,1);
book(_h["i2b_Mbb"],12,1,1);
book(_h["i2b_pTbb"],14,1,1);
book(_h["i2b_pTOnMbb"],15,1,1);
book(_h["ib_nBJets"],1,1,1);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
const DileptonFinder& zfinderE = apply<DileptonFinder>(event, "zfinderE");
const Particles& els = zfinderE.constituents();
const DileptonFinder& zfinderM = apply<DileptonFinder>(event, "zfinderM");
const Particles& mus = zfinderM.constituents();
// default is to run average of Z->ee and Z->mm
// use LMODE option to pick one channel
if ( (els.size() + mus.size()) != 2 ) vetoEvent;
if (_mode == 0 && !(els.size()==2 || mus.size()==2) ) vetoEvent;
else if ( _mode == 1 && !(els.size() == 2 && mus.empty()) ) vetoEvent;
else if ( _mode == 2 && !(els.empty() && mus.size() == 2) ) vetoEvent;
double Vpt = 0, Vy = 0, Veta = 0, Vphi = 0;
if ( els.size()==2 ) {
Vpt = zfinderE.boson().pt()/GeV;
Vphi = zfinderE.boson().phi();
Vy = zfinderE.boson().rapidity();
Veta = zfinderE.boson().eta();
} else {
Vpt = zfinderM.boson().pt()/GeV;
Vphi = zfinderM.boson().phi();
Vy = zfinderM.boson().rapidity();
Veta = zfinderM.boson().eta();
}
Jets jets = apply<JetFinder>(event, "jets").jetsByPt(Cuts::pT>20*GeV && Cuts::absrap < 2.5);
idiscardIfAnyDeltaRLess(jets, els, 0.4);
idiscardIfAnyDeltaRLess(jets, mus, 0.4);
Jets btagged;
const Particles allBs = apply<HeavyHadrons>(event, "HFHadrons").bHadrons(Cuts::pT > 5.0*GeV);
Particles matchedBs;
for (const Jet& j : jets) {
Jet closest_j;
Particle closest_b;
double minDR_j_b = 10;
for (const Particle& bHad : allBs) {
bool alreadyMatched = false;
for (const Particle& bMatched : matchedBs) {
alreadyMatched |= bMatched.isSame(bHad);
}
if (alreadyMatched) continue;
double DR_j_b = deltaR(j, bHad);
if ( DR_j_b <= 0.3 && DR_j_b < minDR_j_b) {
minDR_j_b = DR_j_b;
closest_j = j;
closest_b = bHad;
}
}
if (minDR_j_b < 0.3) {
btagged += closest_j;
matchedBs += closest_b;
}
}
//size_t njets = jets.size();
size_t ntags = btagged.size();
if (ntags < 1) vetoEvent;
_h["ib_nBJets"]->fill(1); //inclusive 1-b
double dYVb = fabs(Vy - btagged[0].rap());
double dEtaVb = fabs(Veta - btagged[0].eta());
double dPhiVb = deltaPhi(Vphi, btagged[0]);
double dRVb = sqrt(dEtaVb*dEtaVb + dPhiVb*dPhiVb);
_h["i1b_ZpT"] ->fill(Vpt/GeV);
_h["i1b_ZY"] ->fill(fabs(Vy));
_h["i1b_dPhiZb"]->fill(dPhiVb);
_h["i1b_dRZb"]->fill(dRVb);
_h["i1b_dYZb"]->fill(dYVb);
_h["i1b_bpT"]->fill(btagged[0].pt()/GeV);
_h["i1b_bY"]->fill(btagged[0].absrap());
if ( ntags>1 ) {
_h["ib_nBJets"]->fill(2); //inclusive 2-b
double dYbb = fabs(btagged[0].rap() - btagged[1].rap());
double dPhibb = deltaPhi(btagged[0], btagged[1]);
double dRbb = deltaR(btagged[0], btagged[1]);
double Mbb = (btagged[0].mom() + btagged[1].mom()).mass()/GeV;
double Ptbb = (btagged[0].mom() + btagged[1].mom()).pt()/GeV;
_h["i2b_ZpT"]->fill(Vpt);
_h["i2b_dPhibb"]->fill(dPhibb);
_h["i2b_dRbb"]->fill(dRbb);
_h["i2b_dYbb"]->fill(dYbb);
_h["i2b_Mbb"]->fill(Mbb);
_h["i2b_pTbb"]->fill(Ptbb);
_h["i2b_pTOnMbb"]->fill(Ptbb/Mbb);
}
}
void finalize() {
// routine accepts both Z->ee and Z->mm
// data corresponds to average
const double sf = _mode? 1.0 : 0.5;
scale(_h, sf * crossSectionPerEvent());
}
private:
size_t _mode;
map<string, Histo1DPtr> _h;
};
RIVET_DECLARE_PLUGIN(ATLAS_2020_I1788444);
}