Rivet analyses

title: CMS_2017_I1634835

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 $p_T^l > 20$ GeV, $|\eta^l| < 2.1$, $71 < m_{ll} < 111$ GeV, and heavy flavour jets with $p_T^{jet} > 25$ GeV and $|\eta^{jet}| <2.5$. 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++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DileptonFinder.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/VetoedFinalState.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 ```