Rivet analyses
K-short and Lambda production in ttbar events at 7 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1746286
Status: VALIDATED
Authors: - Sergio Calvente - Fernando Barreiro - Javier LLorente
References: - Expt page: ATLAS-TOPQ-2016-05 - Eur.Phys.J. C79 (2019) no.12, 1017 - DOI: 10.1140/epjc/s10052-019-7512-y - arXiv: 1907.10862
Beams: p+ p+
Beam energies: (3500.0, 3500.0)GeV
Run details: - ttbar production at 7 TeV. No ctau cut, or set ctau > 100 mm stable so K0S and Lambda decay.
Measurements of KS0 and Λ0 production in tt̄ final states have been performed. They are based on a data sample with integrated luminosity of 4.6 fb−1 from proton-proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a b-tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in tt̄ dileptonic events is found to be well described by current Monte Carlo models for KS0 ans Λ0 production within jets, but not for those produced outside jets.
Source
code:ATLAS_2019_I1746286.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/HeavyHadrons.hh"
namespace Rivet {
class ATLAS_2019_I1746286 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1746286);
/// Book histograms and initialise projections before the run
void init() {
// Set up projections
const FinalState fs(Cuts::abseta < 4.5);
/// Get electrons from truth record
FinalState elec_fs(Cuts::abspid == PID::ELECTRON && Cuts::abseta < 2.47 && Cuts::pT > 25*GeV);
declare(elec_fs, "ELEC_FS");
/// Get muons which pass the initial kinematic cuts:
FinalState muon_fs(Cuts::abspid == PID::MUON && Cuts::abseta < 2.5 && Cuts::pT > 20*GeV);
declare(muon_fs, "MUON_FS");
// get b-hadrons
declare(HeavyHadrons(Cuts::pT > 5*GeV), "BHadrons");
UnstableParticles k0_fs(Cuts::abspid == PID::K0S && Cuts::abseta < 2.5 && Cuts::E > 1*GeV);
declare(k0_fs, "K0_FS");
UnstableParticles lambda_fs(Cuts::abspid == PID::LAMBDA && Cuts::abseta < 2.5 && Cuts::E > 1*GeV);
declare(lambda_fs, "LAMBDA_FS");
// Final state used as input for jet-finding.
// We include everything except the muons and neutrinos
FastJets jets(fs, JetAlg::ANTIKT, 0.4, JetMuons::NONE, JetInvisibles::NONE);
declare(jets, "JETS");
// Book histograms
book(_h["b_k0_pt"], 1, 1, 1);
book(_h["b_k0_x"], 2, 1, 1);
book(_h["b_k0_e"], 3, 1, 1);
book(_h["b_k0_eta"], 4, 1, 1);
book(_d["b_k0_n"], 5, 1, 1);
book(_h["j_k0_pt"], 6, 1, 1);
book(_h["j_k0_x"], 7, 1, 1);
book(_h["j_k0_e"], 8, 1, 1);
book(_h["j_k0_eta"], 9, 1, 1);
book(_d["j_k0_n"], 10, 1, 1);
book(_h["out_k0_pt"], 11, 1, 1);
book(_h["out_k0_e"], 12, 1, 1);
book(_h["out_k0_eta"], 13, 1, 1);
book(_s["out_k0_n"], 14, 1, 1);
book(_h["all_k0_pt"], 15, 1, 1);
book(_h["all_k0_e"], 16, 1, 1);
book(_h["all_k0_eta"], 17, 1, 1);
book(_s["all_k0_n"], 18, 1, 1);
book(_h["all_l_pt"], 19, 1, 1);
book(_h["all_l_e"], 20, 1, 1);
book(_h["all_l_eta"], 21, 1, 1);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
/// Get the various sets of final state particles
const Particles& elecFS = apply<FinalState>(event, "ELEC_FS").particlesByPt();
const Particles& muonFS = apply<FinalState>(event, "MUON_FS").particlesByPt();
const Particles& k0FS = apply<UnstableParticles>(event, "K0_FS").particlesByPt();
const Particles& lambdaFS = apply<UnstableParticles>(event, "LAMBDA_FS").particlesByPt();
// Get all jets with pT > 7 GeV (ATLAS standard jet collection)
Jets jets = apply<FastJets>(event, "JETS").jetsByPt(Cuts::pT > 7*GeV);
// Keep any jets that pass the pt cut
Jets good_jets = select(jets, Cuts::pT > 25*GeV && Cuts::abseta < 2.5);
// Remove jets too close to an electron
idiscardIfAnyDeltaRLess(good_jets, elecFS, 0.2);
// Classify the event type
const size_t nElec = elecFS.size();
const size_t nMuon = muonFS.size();
bool isDilepton = false;
if (nElec == 2 && nMuon == 0) {
if (charge(elecFS[0]) != charge(elecFS[1])) isDilepton = true;
} else if (nElec == 1 && nMuon == 1) {
if (charge(elecFS[0]) != charge(muonFS[0])) isDilepton = true;
} else if (nElec == 0 && nMuon == 2) {
if (charge(muonFS[0]) != charge(muonFS[1])) isDilepton = true;
}
const bool isGoodEvent = (isDilepton && good_jets.size() >= 2);
if (!isGoodEvent) vetoEvent;
// Select b-hadrons
const Particles& bHadrons = apply<HeavyHadrons>(event, "BHadrons").bHadrons();
// Select b-jets as those containing a b-hadron
Jets bjets = discardIfAnyDeltaRLess(good_jets, bHadrons, 0.3);
size_t n_k0_all_visible = 0;
size_t n_k0_out_visible = 0;
size_t n_k0_b_visible = 0;
size_t n_k0_j_visible = 0;
bool isVisible = false;
// Loop over all K0s particles
for (const Particle& k : k0FS) {
if (k.hasStableDescendantWith(Cuts::pid == PID::PIPLUS)) isVisible = true;
if (isVisible) n_k0_all_visible += 1;
_h["all_k0_pt"]->fill(k.pT()/GeV);
_h["all_k0_eta"]->fill(k.abseta());
_h["all_k0_e"]->fill(k.E()/GeV);
bool isJetAssoc = false, isBjet = false;
double minDeltaR = 1000., jetAssocE = 0.;
for (const Jet& j : good_jets) {
const double k0_jetdR = deltaR(j, k);
if (k0_jetdR < 0.4 && k0_jetdR < minDeltaR) {
isJetAssoc = true;
minDeltaR = k0_jetdR;
jetAssocE = j.E();
isBjet = any(bHadrons, DeltaRLess(j, 0.3));
}
}
// K0s not associated to jets
if (!isJetAssoc){
if(isVisible) n_k0_out_visible += 1;
_h["out_k0_pt"]->fill(k.pT()/GeV);
_h["out_k0_eta"]->fill(k.abseta());
_h["out_k0_e"]->fill(k.E()/GeV);
}
//K0s associated to b-jets
if (isJetAssoc && isBjet){
if (isVisible) n_k0_b_visible += 1;
_h["b_k0_pt"]->fill(k.pT()/GeV);
_h["b_k0_eta"]->fill(k.abseta());
_h["b_k0_e"]->fill(k.E()/GeV);
_h["b_k0_x"]->fill(k.E()/jetAssocE);
}
//K0s associated to non b-jets
if(isJetAssoc && !isBjet){
if(isVisible) n_k0_j_visible += 1;
_h["j_k0_pt"]->fill(k.pT()/GeV);
_h["j_k0_eta"]->fill(k.abseta());
_h["j_k0_e"]->fill(k.E()/GeV);
_h["j_k0_x"]->fill(k.E()/jetAssocE);
}
}
// K0s multiplicities
_s["all_k0_n"]->fill(allEdge(n_k0_all_visible));
_s["out_k0_n"]->fill(outEdge(n_k0_out_visible));
_d["b_k0_n"]->fill(n_k0_b_visible);
_d["j_k0_n"]->fill(n_k0_j_visible);
// Loop over all Lambda particles
//size_t n_lambda_all = 0;
for (const Particle& l : lambdaFS) {
//n_lambda_all += 1;
_h["all_l_pt"]->fill(l.pT()/GeV);
_h["all_l_eta"]->fill(l.abseta());
_h["all_l_e"]->fill(l.E()/GeV);
}
}
const string outEdge(const size_t n) {
if (outEdges.empty()) outEdges = _s["out_k0_n"]->xEdges();
if (n > 9) return ""; // otherflow
return outEdges[(n == 9)? 8 : n];
}
const string allEdge(const size_t n) {
if (allEdges.empty()) allEdges = _s["all_k0_n"]->xEdges();
if (n > 11) return ""; // otherflow
return allEdges[(n == 10 || n == 11)? 9 : n];
}
// Histogram normalization to the number of events passing the cuts
void finalize() {
const double sf = 1.0 / _s["all_k0_n"]->sumW();
scale(_h, sf);
scale(_d, sf);
scale(_s, sf);
}
private:
// Counters
map<string, Histo1DPtr> _h;
map<string, BinnedHistoPtr<int>> _d;
map<string, BinnedHistoPtr<string>> _s;
vector<string> outEdges, allEdges;
};
RIVET_DECLARE_PLUGIN(ATLAS_2019_I1746286);
}