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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
  • 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 $\sqrt{s} = 13 \text{TeV}$ 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 $p_{T}^{Z} < 50 \text{GeV}$.

Source code: CMS_2019_I1753680.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/DressedLeptons.hh"
#include "Rivet/Projections/ZFinder.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
    DEFAULT_RIVET_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
      FinalState fs;
      Cut cut = Cuts::abseta < 2.4 && Cuts::pT > 25*GeV;

      ZFinder zeeFind(fs, cut, PID::ELECTRON, 76.1876*GeV, 106.1876*GeV, 0.1, ZFinder::ChargedLeptons::PROMPT, ZFinder::ClusterPhotons::NODECAY, ZFinder::AddPhotons::YES );
      declare(zeeFind, "ZeeFind");
      ZFinder zmmFind(fs, cut, PID::MUON    , 76.1876*GeV, 106.1876*GeV, 0.1, ZFinder::ChargedLeptons::PROMPT, ZFinder::ClusterPhotons::NODECAY, ZFinder::AddPhotons::YES );
      declare(zmmFind, "ZmmFind");
      
      // Book histograms
      book(_h_Zmm_absY          , 26, 1, 1);
      book(_h_Zee_absY          , 26, 1, 2);
      book(_h_Zll_absY          , 26, 1, 3);
      book(_h_Zmm_pt            , 27, 1, 1);
      book(_h_Zee_pt            , 27, 1, 2);
      book(_h_Zll_pt            , 27, 1, 3);
      book(_h_Zmm_phiStar       , 28, 1, 1);
      book(_h_Zee_phiStar       , 28, 1, 2);
      book(_h_Zll_phiStar       , 28, 1, 3);
      book(_h_Zll_pt_Y0         , 29, 1, 1);
      book(_h_Zll_pt_Y1         , 29, 1, 2);
      book(_h_Zll_pt_Y2         , 29, 1, 3);
      book(_h_Zll_pt_Y3         , 29, 1, 4);
      book(_h_Zll_pt_Y4         , 29, 1, 5);
      
      book(_h_Zll_pt_norm       , 30, 1, 1);
      book(_h_Zll_phiStar_norm  , 31, 1, 1);
      book(_h_Zll_absY_norm     , 32, 1, 1);
      book(_h_Zll_pt_Y0_norm    , 33, 1, 1);
      book(_h_Zll_pt_Y1_norm    , 33, 1, 2);
      book(_h_Zll_pt_Y2_norm    , 33, 1, 3);
      book(_h_Zll_pt_Y3_norm    , 33, 1, 4);
      book(_h_Zll_pt_Y4_norm    , 33, 1, 5);
      
    }
    

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      
      const ZFinder& zeeFS = apply<ZFinder>(event, "ZeeFind");
      const ZFinder& zmumuFS = apply<ZFinder>(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());
        _h_Zee_phiStar->fill(phiStar);
      }
      else if (mm_event) {
        _h_Zmm_absY->fill(zcand.absrap());
        _h_Zmm_pt->fill(zcand.pt());
        _h_Zmm_phiStar->fill(phiStar);
      }

      _h_Zll_pt->fill(zcand.pt());
      _h_Zll_pt_norm->fill(zcand.pt());
      _h_Zll_phiStar->fill(phiStar);
      _h_Zll_phiStar_norm->fill(phiStar);
      _h_Zll_absY->fill(zcand.absrap());
      _h_Zll_absY_norm->fill(zcand.absrap());

      if      (zcand.absrap()<0.4) {
        _h_Zll_pt_Y0->fill(zcand.pt());
        _h_Zll_pt_Y0_norm->fill(zcand.pt());
      }
      else if (zcand.absrap()<0.8) {
        _h_Zll_pt_Y1->fill(zcand.pt());
        _h_Zll_pt_Y1_norm->fill(zcand.pt());
      }
      else if (zcand.absrap()<1.2) {
        _h_Zll_pt_Y2->fill(zcand.pt());
        _h_Zll_pt_Y2_norm->fill(zcand.pt());
      }
      else if (zcand.absrap()<1.6) {
        _h_Zll_pt_Y3->fill(zcand.pt());
        _h_Zll_pt_Y3_norm->fill(zcand.pt());
      }
      else if (zcand.absrap()<2.4) {
        _h_Zll_pt_Y4->fill(zcand.pt());
        _h_Zll_pt_Y4_norm->fill(zcand.pt());
      }

    }
    
    void normalizeToSum(Histo1DPtr hist) {
      double sum = 0.;
      for (size_t i = 0; i < hist->numBins(); ++i) {
        sum += hist->bin(i).height();
      }
      scale(hist, 1./sum);
    }

    /// 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_Zll_pt,      norm);
      scale(_h_Zll_absY,    norm);
      scale(_h_Zll_phiStar, norm);
      scale(_h_Zll_pt_Y0,   norm);
      scale(_h_Zll_pt_Y1,   norm);
      scale(_h_Zll_pt_Y2,   norm);
      scale(_h_Zll_pt_Y3,   norm);
      scale(_h_Zll_pt_Y4,   norm);

      normalizeToSum(_h_Zll_pt_norm);
      normalizeToSum(_h_Zll_absY_norm);
      normalizeToSum(_h_Zll_phiStar_norm);
      normalizeToSum(_h_Zll_pt_Y0_norm);
      normalizeToSum(_h_Zll_pt_Y1_norm);
      normalizeToSum(_h_Zll_pt_Y2_norm);
      normalizeToSum(_h_Zll_pt_Y3_norm);
      normalizeToSum(_h_Zll_pt_Y4_norm);

    }

    //@}

  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;

    Histo1DPtr   _h_Zll_pt, _h_Zll_phiStar, _h_Zll_absY;
    Histo1DPtr   _h_Zll_pt_Y0, _h_Zll_pt_Y1, _h_Zll_pt_Y2, _h_Zll_pt_Y3, _h_Zll_pt_Y4;

    Histo1DPtr   _h_Zll_pt_norm, _h_Zll_phiStar_norm, _h_Zll_absY_norm;
    Histo1DPtr   _h_Zll_pt_Y0_norm, _h_Zll_pt_Y1_norm, _h_Zll_pt_Y2_norm, _h_Zll_pt_Y3_norm, _h_Zll_pt_Y4_norm;

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(CMS_2019_I1753680);


}