Rivet analyses
Measurement of associated Z + charm production in proton-proton collisions at sqrts = 8 TeV
Experiment: CMS (LHC)
Inspire ID: 1634835
Status: VALIDATED
Authors: - Hannes Jung - Juan Pablo Fernandez
References: - Eur.Phys.J.C 78 (2018) 287 - DOI: 10.1140/epjc/s10052-018-5752-x - arXiv: 1711.02143 - Expt page: CMS-SMP-15-009
Beams: p+ p+
Beam energies: (4000.0, 4000.0)GeV
Run details: - Z+c production
A study of the associated production of a Z boson and a charm quark jet (Z+c) and a comparison to production with a b quark jet (Z+b), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample cor- responding to an integrated luminosity of 19.7 fb−1, collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are iden- tified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with pTl > 20 GeV, |ηl| < 2.1, 71 < mll < 111 GeV, and heavy flavour jets with pTjet > 25 GeV and |ηjet| < 2.5. The Z + c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet.
Source
code:CMS_2017_I1634835.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/DileptonFinder.hh"
#include "Rivet/Tools/Cuts.hh"
namespace Rivet {
/// @brief Z+charm at 8 TeV
class CMS_2017_I1634835 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2017_I1634835);
/// @name Analysis methods
///@{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
DileptonFinder zeeFinder(91.2*GeV, 0.1, Cuts::abseta < 2.1 && Cuts::pT > 20*GeV &&
Cuts::abspid == PID::ELECTRON, Cuts::massIn(71*GeV, 111*GeV));
declare(zeeFinder, "ZeeFinder");
DileptonFinder zmumuFinder(91.2*GeV, 0.1, Cuts::abseta < 2.1 && Cuts::pT > 20*GeV &&
Cuts::abspid == PID::MUON, Cuts::massIn(71*GeV, 111*GeV));
declare(zmumuFinder, "ZmumuFinder");
VetoedFinalState jetConstits;
jetConstits.addVetoOnThisFinalState(zeeFinder);
jetConstits.addVetoOnThisFinalState(zmumuFinder);
FastJets akt04Jets(jetConstits, JetAlg::ANTIKT, 0.4);
declare(akt04Jets, "AntiKt04Jets");
book(_h_Z_pt_cjet, 4, 1, 1);
book(_h_pt_cjet, 5, 1, 1);
book(_h_Z_pt_bjet, "TMP/Z_pt_bjet", refData(4, 1, 2));
book(_h_pt_bjet, "TMP/pt_bjet", refData(5, 1, 2));
// book ratio histos
book(_h_R_Z_pt_cjet, 4, 1, 2);
book(_h_R_jet_pt_cjet, 5, 1, 2);
book(counter_ee, "TMP/counter_ee");
book(counter_mm, "TMP/counter_mm");
}
/// Perform the per-event analysis
void analyze(const Event& event) {
const DileptonFinder& zeeFS = apply<DileptonFinder>(event, "ZeeFinder");
const DileptonFinder& zmumuFS = apply<DileptonFinder>(event, "ZmumuFinder");
const Particles& zees = zeeFS.bosons();
const Particles& zmumus = zmumuFS.bosons();
// We did not find exactly one Z. No good.
if (zees.size() + zmumus.size() != 1) {
MSG_DEBUG("Did not find exactly one good Z candidate");
vetoEvent;
}
Particles leptons;
Particle zcand;
if (zees.size() == 1) {
leptons = zeeFS.leptons();
zcand = zees[0];
counter_ee->fill();
}
if (zmumus.size() == 1) {
leptons = zmumuFS.leptons();
zcand = zmumus[0];
counter_mm->fill();
}
// Cluster jets
// NB. Veto has already been applied on leptons and photons used for dressing
const FastJets& fj = apply<FastJets>(event, "AntiKt04Jets");
Jets goodjets = fj.jetsByPt(Cuts::abseta < 2.5 && Cuts::pT > 25*GeV);
idiscardIfAnyDeltaRLess(goodjets, leptons, 0.5);
// We don't care about events with no isolated jets
if (goodjets.empty()) {
MSG_DEBUG("No jets in event");
vetoEvent;
}
Jets jc_final;
Jets jb_final;
// identification of bjets
int n_btag = count(goodjets, hasBTag());
for (const Jet& j : goodjets) {
if (j.cTagged() && n_btag == 0) {
jc_final.push_back(j);
}
if (j.bTagged()) {
jb_final.push_back(j);
}
}
// histogram filling
if (goodjets.size() > 0) {
if (jc_final.size() > 0) {
_h_pt_cjet->fill(jc_final[0].pt()/GeV);
_h_Z_pt_cjet->fill(zcand.pt()/GeV);
}
if (jb_final.size() > 0) {
_h_pt_bjet->fill(jb_final[0].pt()/GeV);
_h_Z_pt_bjet->fill(zcand.pt()/GeV);
}
}
}
/// Normalise histograms etc., after the run
void finalize() {
double norm = (sumOfWeights() != 0) ? crossSection() / picobarn / sumOfWeights() : 1.0;
// account if we have electrons and muons in the sample
if ((counter_ee->val() > 1.) && (counter_mm->val() > 1.)) {
norm = norm / 2.;
}
divide(_h_pt_cjet, _h_pt_bjet, _h_R_jet_pt_cjet);
divide(_h_Z_pt_cjet, _h_Z_pt_bjet, _h_R_Z_pt_cjet);
scale(_h_Z_pt_cjet, norm);
scale(_h_pt_cjet, norm);
}
///@}
/// @name Histograms
Histo1DPtr _h_pt_cjet;
Histo1DPtr _h_pt_bjet;
Histo1DPtr _h_Z_pt_cjet, _h_Z_pt_bjet;
Estimate1DPtr _h_R_jet_pt_cjet;
Estimate1DPtr _h_R_Z_pt_cjet;
CounterPtr counter_ee, counter_mm;
};
RIVET_DECLARE_PLUGIN(CMS_2017_I1634835);
} // namespace Rivet