Rivet analyses

title: CMS_2019_I1753680

Measurements of differential Z boson production cross sections in proton-proton collisions at 13 TeV

Experiment: CMS (LHC)

Inspire ID: 1753680

Status: VALIDATED

Authors: - cms-pag-conveners-smp@cern.ch - Jay Lawhorn - Markus Seidel

References: - arXiv: 1909.04133 - Expt page: CMS-SMP-17-010 - JHEP 12 (2019) 061

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - pp to Z interactions at $\sqrt{s} = 13$ TeV. Data collected by CMS during the year 2016.

Measurements are presented of the differential cross sections for Z bosons produced in proton-proton collisions at $\sqrt{s} = 13~\TeV$ and decaying to muons and electrons. The data analyzed were collected in 2016 with the CMS detector at the LHC and correspond to an integrated luminosity of $35.9/fb$. The measured fiducial inclusive product of cross section and branching fraction agrees with next-to-next-to-leading order quantum chromodynamics calculations. Differential cross sections of the transverse momentum \pt, the optimized angular variable $\phi^{}_{\eta}$, and the rapidity of lepton pairs are measured. The data are corrected for detector effects and compared to theoretical predictions using fixed order, resummed, and parton shower calculations. The uncertainties of the measured normalized cross sections are smaller than 0.5% for $\phi^{}{\eta} < 0.5$ and for $p{T}^{Z} < 50~\GeV$.

Source code:CMS_2019_I1753680.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/LeptonFinder.hh"

namespace Rivet {

/// @brief Measurements of differential Z boson production cross sections in proton-proton collisions at 13 TeV class CMS_2019_I1753680 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2019_I1753680);


/// @name Analysis methods
/// @{

/// Book histograms and initialise projections before the run
void init() {

  // Get options from the new option system
  // default to combined.
  _mode = 2;
  if (getOption("LMODE") == "EL") _mode = 0;
  if (getOption("LMODE") == "MU") _mode = 1;
  if (getOption("LMODE") == "EMU") _mode = 2;

  // Initialise and register projections
  Cut cut = Cuts::abseta < 2.4 && Cuts::pT > 25 * GeV;
  DileptonFinder zeeFind(91.2 * GeV, 0.1, cut && Cuts::abspid == PID::ELECTRON,
                         Cuts::massIn(76.2 * GeV, 106.2 * GeV));
  declare(zeeFind, "ZeeFind");
  DileptonFinder zmmFind(91.2 * GeV, 0.1, cut && Cuts::abspid == PID::MUON,
                         Cuts::massIn(76.2 * GeV, 106.2 * GeV));
  declare(zmmFind, "ZmmFind");

  // Book histograms
  book(_h_Zmm_absY, 26, 1, 1);
  book(_h_Zee_absY, 26, 1, 2);
  book(_h["absY"], 26, 1, 3);
  book(_h_Zmm_pt, 27, 1, 1);
  book(_h_Zee_pt, 27, 1, 2);
  book(_h["pt"], 27, 1, 3);
  book(_h_Zmm_phiStar, 28, 1, 1);
  book(_h_Zee_phiStar, 28, 1, 2);
  book(_h["phiStar"], 28, 1, 3);
  book(_h["pt_Y0"], 29, 1, 1);
  book(_h["pt_Y1"], 29, 1, 2);
  book(_h["pt_Y2"], 29, 1, 3);
  book(_h["pt_Y3"], 29, 1, 4);
  book(_h["pt_Y4"], 29, 1, 5);

  book(_h_norm["pt"], 30, 1, 1);
  book(_h_norm["phiStar"], 31, 1, 1);
  book(_h_norm["absY"], 32, 1, 1);
  book(_h_norm["pt_Y0"], 33, 1, 1);
  book(_h_norm["pt_Y1"], 33, 1, 2);
  book(_h_norm["pt_Y2"], 33, 1, 3);
  book(_h_norm["pt_Y3"], 33, 1, 4);
  book(_h_norm["pt_Y4"], 33, 1, 5);
}


/// Perform the per-event analysis
void analyze(const Event& event) {

  const DileptonFinder& zeeFS = apply<DileptonFinder>(event, "ZeeFind");
  const DileptonFinder& zmumuFS = apply<DileptonFinder>(event, "ZmmFind");

  const Particles& zees = zeeFS.bosons();
  const Particles& zmumus = zmumuFS.bosons();

  if (zees.size() + zmumus.size() != 1) {
    MSG_DEBUG("Did not find exactly one good Z candidate");
    vetoEvent;
  }

  //event identification depending on mass window
  bool ee_event = false;
  bool mm_event = false;

  if (zees.size() == 1) {
    ee_event = true;
  }
  if (zmumus.size() == 1) {
    mm_event = true;
  }

  if (ee_event && _mode == 1) vetoEvent;
  if (mm_event && _mode == 0) vetoEvent;

  const Particles& theLeptons = ee_event ? zeeFS.constituents() : zmumuFS.constituents();
  const Particle& lminus = theLeptons[0].charge() < 0 ? theLeptons[0] : theLeptons[1];
  const Particle& lplus = theLeptons[0].charge() < 0 ? theLeptons[1] : theLeptons[0];

  //calculate phi*
  const double thetaStar = acos(tanh(0.5 * (lminus.eta() - lplus.eta())));
  const double dPhi = M_PI - deltaPhi(lminus, lplus);
  const double phiStar = tan(0.5 * dPhi) * sin(thetaStar);

  const Particle& zcand = ee_event ? zees[0] : zmumus[0];

  if (ee_event) {
    _h_Zee_absY->fill(zcand.absrap());
    _h_Zee_pt->fill(zcand.pt() / GeV);
    _h_Zee_phiStar->fill(phiStar);
  }
  else if (mm_event) {
    _h_Zmm_absY->fill(zcand.absrap());
    _h_Zmm_pt->fill(zcand.pt() / GeV);
    _h_Zmm_phiStar->fill(phiStar);
  }

  _h["pt"]->fill(zcand.pt() / GeV);
  _h_norm["pt"]->fill(zcand.pt() / GeV);
  _h["phiStar"]->fill(phiStar);
  _h_norm["phiStar"]->fill(phiStar);
  _h["absY"]->fill(zcand.absrap());
  _h_norm["absY"]->fill(zcand.absrap());

  if (zcand.absrap() < 0.4) {
    _h["pt_Y0"]->fill(zcand.pt() / GeV);
    _h_norm["pt_Y0"]->fill(zcand.pt() / GeV);
  }
  else if (zcand.absrap() < 0.8) {
    _h["pt_Y1"]->fill(zcand.pt() / GeV);
    _h_norm["pt_Y1"]->fill(zcand.pt() / GeV);
  }
  else if (zcand.absrap() < 1.2) {
    _h["pt_Y2"]->fill(zcand.pt() / GeV);
    _h_norm["pt_Y2"]->fill(zcand.pt() / GeV);
  }
  else if (zcand.absrap() < 1.6) {
    _h["pt_Y3"]->fill(zcand.pt() / GeV);
    _h_norm["pt_Y3"]->fill(zcand.pt() / GeV);
  }
  else if (zcand.absrap() < 2.4) {
    _h["pt_Y4"]->fill(zcand.pt() / GeV);
    _h_norm["pt_Y4"]->fill(zcand.pt() / GeV);
  }
}

/// Normalise histograms etc., after the run
void finalize() {

  double norm = (sumOfWeights() != 0) ? crossSection() / picobarn / sumOfWeights() : 1.0;

  scale(_h_Zmm_pt, norm);
  scale(_h_Zmm_absY, norm);
  scale(_h_Zmm_phiStar, norm);

  scale(_h_Zee_pt, norm);
  scale(_h_Zee_absY, norm);
  scale(_h_Zee_phiStar, norm);

  // when running in combined mode, need to average to get lepton xsec
  if (_mode == 2) norm /= 2.;
  scale(_h, norm);

  for (auto& item : _h_norm) {
    const double rho = item.second->densitySum(false);
    if (rho) scale(item.second, 1.0 / rho);
  }
}

/// @}

protected:

size_t _mode;

/// @name Histograms

private:

Histo1DPtr _h_Zmm_pt, _h_Zmm_phiStar, _h_Zmm_absY;
Histo1DPtr _h_Zee_pt, _h_Zee_phiStar, _h_Zee_absY;

map<string, Histo1DPtr> _h;
map<string, Histo1DPtr> _h_norm;

};

RIVET_DECLARE_PLUGIN(CMS_2019_I1753680);

} ```