Rivet analyses

title: CMS_2019_I1705068

Measurement of associated production of a W boson and a charm quark in proton-proton collisions at 13 TeV

Experiment: CMS (LHC)

Inspire ID: 1705068

Status: VALIDATED

Authors: - cms-pag-conveners-smp@cern.ch - Svenja Pflitsch - Katerina Lipka

References: - Eur.Phys.J. C79 (2019) no.3, 269 - DOI:10.1140/epjc/s10052-019-6752-1 - arXiv: 1811.10021 - Expt page: CMS-SMP-17-014

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - 13 TeV $pp \to W+c$.

Measurements are presented of associated production of a W boson and a charm quark (W+c) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of $35.7 fb^{-1}$ collected by the CMS experiment at the CERN LHC. The W bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of $D(2010)^{\pm}$ mesons that decay via $D(2010)^{\pm} \to D^{0} + \pi^{pm} \to K^{\mp} + \pi^{pm} + \pi^{pm}$. A parton-level cross section is measured in the fiducial region defined by the muon transverse momentum $\p_{T}^{\mu} > 26 GeV$, muon pseudorapidity $\abs{\eta^{\mu}} < 2.4$, and charm quark transverse momentum $p_{T}^{c} > 5\GeV$. The cross section is also measured differentially as a function of the pseudorapidity of the muon from the W boson decay. A particle-level cross section is measured in the fiducial region defined by the muon transverse momentum $\p_{T}^{\mu} > 26 GeV$, muon pseudorapidity $\abs{\eta^{\mu}} < 2.4$, D(2010)^{\pm} transverse momentum $p_{T}^{D} > 5\GeV$ and D(2010)^{\pm} pseudorapidity $\abs{\eta^{D}} < 2.4$. The particle-level cross section has been implemented in the Rivet plugin.

Source code:CMS_2019_I1705068.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/LeptonFinder.hh"

include "Rivet/Projections/MissingMomentum.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// W + charm quark in proton-proton collisions at 13 TeV class CMS_2019_I1705068 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2019_I1705068);


/// Initialise analyis
void init() {

  // Projections
  declare(MissingMom(), "MET");
  LeptonFinder lf(0.1, Cuts::abseta < 2.4 && Cuts::abspid == PID::MUON);
  declare(lf, "Leptons");

  UnstableParticles dst(Cuts::pT > 5 * GeV && Cuts::abseta < 2.4);
  declare(dst, "Dstar");

  // Particle-Level histograms from the paper:
  book(_hist_WplusMinus_MuAbseta, "d04-x01-y01");
  book(_hist_Wplus_MuAbseta, "d05-x01-y01");
  book(_hist_Wminus_MuAbseta, "d06-x01-y01");
}


void analyze(const Event& event) {

  // Identify the closest-matching mu+MET to m == mW
  const P4& pmiss = apply<MissingMom>(event, "MET").missingMom();
  const Particles& mus = apply<LeptonFinder>(event, "Leptons").particles();
  const Particles mus_mtfilt = select(mus, [&](const Particle& m) { return mT(m, pmiss) > 0 * GeV; });
  const int imfound = closestMatchIndex(mus_mtfilt, pmiss, Kin::mass, 80.4 * GeV);

  // No MET or MT cut at generator level
  if (imfound < 0) vetoEvent;
  const Particle& lepton0 = mus_mtfilt[imfound];
  const double pt0 = lepton0.pT();
  const double eta0 = lepton0.abseta();
  const int muID = lepton0.pid();
  if (eta0 > 2.4 || pt0 < 26 * GeV) vetoEvent;

  // D* selection:
  // OS = W boson and D* Meson have Opposite (charge) Signs
  // SS = W Boson and D* Meson have Same (charge) Signs
  // Associated W+c only has OS contributions,
  // W+ccbar (ccbar from gluon splitting) has equal probability to be OS or SS
  // OS-SS to remove the gluon splitting background

  const UnstableParticles& dst = apply<UnstableParticles>(event, "Dstar");
  for (const Particle& p : dst.particles()) {
    if (muID == -13 && p.pid() == -413) { // OS
      _hist_Wplus_MuAbseta->fill(eta0);
      _hist_WplusMinus_MuAbseta->fill(eta0);
    }
    else if (muID == 13 && p.pid() == 413) { // OS
      _hist_Wminus_MuAbseta->fill(eta0);
      _hist_WplusMinus_MuAbseta->fill(eta0);
    }
    else if (muID == -13 && p.pid() == 413) { // SS
      _hist_Wplus_MuAbseta->fill(eta0 * -1);
      _hist_WplusMinus_MuAbseta->fill(eta0 * -1);
    }
    else if (muID == 13 && p.pid() == -413) { // SS
      _hist_Wminus_MuAbseta->fill(eta0 * -1);
      _hist_WplusMinus_MuAbseta->fill(eta0 * -1);
    }
  }
}


void finalize() {
  scale(_hist_Wplus_MuAbseta, crossSection() / picobarn / sumOfWeights());
  scale(_hist_Wminus_MuAbseta, crossSection() / picobarn / sumOfWeights());
  scale(_hist_WplusMinus_MuAbseta, crossSection() / picobarn / sumOfWeights());
}


Histo1DPtr _hist_Wplus_MuAbseta;
Histo1DPtr _hist_Wminus_MuAbseta;
Histo1DPtr _hist_WplusMinus_MuAbseta;

};

RIVET_DECLARE_PLUGIN(CMS_2019_I1705068);

} ```