Rivet analyses

Measurement of the underlying event using inclusive Z-boson production in proton-proton collisions at $\sqrt{s} = 13$ TeV

Experiment: CMS (LHC)

Inspire ID: 1635889

Status: VALIDATED

Authors: - Rajat Gupta - Ramandeep Kumar - Ankita Mehta - Sunil Bansal - J.B. Singh

References: - CMS FSQ-16-008 - arXiv: 1711.04299

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - Drell-Yan events with $Z/\gamma^* \to \mu\mu$.

Measurement of the underlying event activity, in proton-proton collisions at a centre-of-mass energy of 13 TeV$, performed using inclusive Z-boson events collected by the CMS experiment at the Large Hadron Collider. The analyzed data corresponds to an integrated luminosity of 2.1 fb${}^{-1}$. The underlying event activity is quantified in terms of charged particle multiplicity and their scalar sum of their transverse momentum in different topological regions defined with respect to the resultatnt azimuthal direction of the two muons coming from the decay of a Z-boson. The distributions are unfolded to stable charged-particle level and are compared with predictions from various simulations, as well as with the measurements at a centre-of-mass energy of 1.96 TeV$ and 7 TeV by the CDF and CMS experiments.

Source code:CMS_2017_I1635889.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/DileptonFinder.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"

namespace Rivet {


  /// Underlying event activity in the Drell-Yan process at 13 TeV
  class CMS_2017_I1635889 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2017_I1635889);


    /// Initialization
    void init() {

      /// @note Using a bare muon Z (but with a clustering radius!?)
      Cut cut = Cuts::abseta < 2.4 && Cuts::pT > 10 * GeV;
      DileptonFinder zfinder(91.2 * GeV, 0.2, cut && Cuts::abspid == PID::MUON,
                             Cuts::massIn(81 * GeV, 101 * GeV));
      declare(zfinder, "DileptonFinder");

      ChargedFinalState cfs(zfinder.remainingFinalState());
      declare(cfs, "cfs");

      book(_h_Nchg_towards_pTmumu, 1, 1, 1);
      book(_h_Nchg_transverse_pTmumu, 2, 1, 1);
      book(_h_Nchg_away_pTmumu, 3, 1, 1);
      book(_h_pTsum_towards_pTmumu, 4, 1, 1);
      book(_h_pTsum_transverse_pTmumu, 5, 1, 1);
      book(_h_pTsum_away_pTmumu, 6, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const DileptonFinder& zfinder = apply<DileptonFinder>(event, "DileptonFinder");

      if (zfinder.bosons().size() != 1) vetoEvent;
      if (zfinder.constituents()[0].pT() < 20 && zfinder.constituents()[1].pT() < 20) vetoEvent;
      //std::cout<<"pt[0] = "<<zfinder.constituents()[0].pT()<<"pt[1] = "<<zfinder.constituents()[1].pT()<<std::endl;
      double Zpt = zfinder.bosons()[0].pT() / GeV;
      double Zphi = zfinder.bosons()[0].phi();
      //double Zmass = zfinder.bosons()[0].mass()/GeV;

      Particles particles = apply<ChargedFinalState>(event, "cfs")
                                .particlesByPt(Cuts::pT > 0.5 * GeV && Cuts::abseta < 2.0);

      int nTowards = 0;
      int nTransverse = 0;
      int nAway = 0;
      double ptSumTowards = 0;
      double ptSumTransverse = 0;
      double ptSumAway = 0;

      for (const Particle& p : particles) {
        double dphi = fabs(deltaPhi(Zphi, p.phi()));
        double pT = p.pT();

        if (dphi < M_PI / 3) {
          nTowards++;
          ptSumTowards += pT;
        }
        else if (dphi < 2. * M_PI / 3) {
          nTransverse++;
          ptSumTransverse += pT;
        }
        else {
          nAway++;
          ptSumAway += pT;
        }

      } // Loop over particles


      const double area = 8. / 3. * M_PI;
      _h_Nchg_towards_pTmumu->fill(Zpt, 1. / area * nTowards);
      _h_Nchg_transverse_pTmumu->fill(Zpt, 1. / area * nTransverse);
      _h_Nchg_away_pTmumu->fill(Zpt, 1. / area * nAway);
      _h_pTsum_towards_pTmumu->fill(Zpt, 1. / area * ptSumTowards);
      _h_pTsum_transverse_pTmumu->fill(Zpt, 1. / area * ptSumTransverse);
      _h_pTsum_away_pTmumu->fill(Zpt, 1. / area * ptSumAway);
    }


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


  private:


    /// @name Histogram objects
    /// @{
    Profile1DPtr _h_Nchg_towards_pTmumu;
    Profile1DPtr _h_Nchg_transverse_pTmumu;
    Profile1DPtr _h_Nchg_away_pTmumu;
    Profile1DPtr _h_pTsum_towards_pTmumu;
    Profile1DPtr _h_pTsum_transverse_pTmumu;
    Profile1DPtr _h_pTsum_away_pTmumu;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CMS_2017_I1635889);

}