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CMS_2013_I1209721

Azimuthal correlations and event shapes in $Z$ + jets in $pp$ collisions at 7 TeV
Experiment: CMS (LHC)
Inspire ID: 1209721
Status: VALIDATED
Authors:
  • Io Odderskov
References:
  • http://cms.cern.ch/iCMS/analysisadmin/cadi?ancode=EWK-11-021
  • https://cds.cern.ch/record/1503578
  • http://inspirehep.net/record/1209721
  • arXiv: 1301.1646
  • Submitted to Phys. Lett. B
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Run MC generators with Z decaying to leptonic modes at 7TeV comEnergy

Measurements are presented of event shapes and azimuthal correlations in the inclusive production of a Z boson in association with jets in proton-proton collisions. The data correspond to an integrated luminosity of 5.0/fb, collected with the CMS detector at the CERN LHC at $\sqrt{s} = 7$\;TeV. This to test perturbative QCD predictions and evaluate a substantial background to most physics channels. Studies performed as a function of jet multiplicity for inclusive $Z$ boson production and for $Z$ bosons with transverse-momenta greater than 150\;GeV, are compared to predictions from Monte Carlo event generators that include leading-order multiparton matrix-element (with up to four hard partons in the final state) and next-to-leading-order simulations of Z + 1-jet events. The results are corrected for detector effects, and can therefore be used as input to improve models for describing these processes.

Source code: CMS_2013_I1209721.cc
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#include "Rivet/Analysis.hh"
#include "Rivet/Tools/BinnedHistogram.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/ZFinder.hh"
#include "Rivet/Projections/Thrust.hh"

namespace Rivet {

  


  /// CMS Z+jets delta(phi) and jet thrust measurement at 7 TeV
  class CMS_2013_I1209721 : public Analysis {
  public:

    CMS_2013_I1209721()
      : Analysis("CMS_2013_I1209721")
    {    }


    /// Book projections and histograms
    void init() {
      // Full final state
      const FinalState fs(-5.0,5.0);
      declare(fs, "FS");
      // Z finders for electrons and muons
      Cut cuts = Cuts::abseta < 2.4 && Cuts::pT > 20*GeV;
      const ZFinder zfe(fs, cuts, PID::ELECTRON, 71*GeV, 111*GeV);
      const ZFinder zfm(fs, cuts, PID::MUON,     71*GeV, 111*GeV);
      declare(zfe, "ZFE");
      declare(zfm, "ZFM");
      // Jets
      const FastJets jets(fs, FastJets::ANTIKT, 0.5);
      declare(jets, "JETS");

      // Book histograms from data
      for (size_t i = 0; i < 2; ++i) {
        _histDeltaPhiZJ1_1[i]  = bookHisto1D(1+i*9, 1, 1);
        _histDeltaPhiZJ1_2[i]  = bookHisto1D(2+i*9, 1, 1);
        _histDeltaPhiZJ1_3[i]  = bookHisto1D(4+i*9, 1, 1);
        _histDeltaPhiZJ2_3[i]  = bookHisto1D(5+i*9, 1, 1);
        _histDeltaPhiZJ3_3[i]  = bookHisto1D(3+i*9, 1, 1);
        _histDeltaPhiJ1J2_3[i] = bookHisto1D(6+i*9, 1, 1);
        _histDeltaPhiJ1J3_3[i] = bookHisto1D(7+i*9, 1, 1);
        _histDeltaPhiJ2J3_3[i] = bookHisto1D(8+i*9, 1, 1);
        _histTransvThrust[i]   = bookHisto1D(9+i*9, 1, 1);
      }
    }


    void analyze(const Event& event) {
      const double weight = event.weight();

      // Apply the Z finders
      const ZFinder& zfe = apply<ZFinder>(event, "ZFE");
      const ZFinder& zfm = apply<ZFinder>(event, "ZFM");

      // Choose the Z candidate (there must be one)
      if (zfe.empty() && zfm.empty()) vetoEvent;
      const ParticleVector& z = !zfm.empty() ? zfm.bosons() : zfe.bosons();
      const ParticleVector& leptons = !zfm.empty() ? zfm.constituents() : zfe.constituents();

      // Determine whether we are in the boosted regime
      const bool is_boosted = (z[0].pT() > 150*GeV);

      // Build the jets
      const FastJets& jetfs = apply<FastJets>(event, "JETS");
      const Jets& jets = jetfs.jetsByPt(Cuts::pT > 50*GeV && Cuts::abseta < 2.5);

      // Clean the jets against the lepton candidates, as in the paper, with a deltaR cut of 0.4 against the clustered leptons
      vector<const Jet*> cleanedJets;
      for (size_t i = 0; i < jets.size(); ++i) {
        bool isolated = true;
        for (size_t j = 0; j < 2; ++j) {
          if (deltaR(leptons[j], jets[i]) < 0.4) {
            isolated = false;
            break;
          }
        }
        if (isolated) cleanedJets.push_back(&jets[i]);
      }

      // Require at least 1 jet
      const unsigned int Njets = cleanedJets.size();
      if (Njets < 1) vetoEvent;

      // Now compute the thrust
      // Collect Z and jets transverse momenta to calculate transverse thrust
      vector<Vector3> momenta;
      momenta.clear();
      Vector3 mom = z[0].p3();
      mom.setZ(0);
      momenta.push_back(mom);

      for (size_t i = 0; i < cleanedJets.size(); ++i) {
        Vector3 mj = cleanedJets[i]->momentum().p3();
        mj.setZ(0);
        momenta.push_back(mj);
      }

      if (momenta.size() <= 2){
        // We need to use a ghost so that Thrust.calc() doesn't return 1.
        momenta.push_back(Vector3(0.0000001,0.0000001,0.));
      }

      Thrust thrust; thrust.calc(momenta);
      const double T = thrust.thrust();
      FILLx2(_histTransvThrust, is_boosted, log(max(1-T, 1e-6)), weight);

      const double dphiZJ1 = deltaPhi(z[0], *cleanedJets[0]);
      FILLx2(_histDeltaPhiZJ1_1, is_boosted, dphiZJ1, weight);
      if (Njets > 1) {
        FILLx2(_histDeltaPhiZJ1_2, is_boosted, dphiZJ1, weight);
        if (Njets > 2) {
          FILLx2(_histDeltaPhiZJ1_3,  is_boosted, dphiZJ1, weight);
          FILLx2(_histDeltaPhiZJ2_3,  is_boosted, deltaPhi(z[0], *cleanedJets[1]), weight);
          FILLx2(_histDeltaPhiZJ3_3,  is_boosted, deltaPhi(z[0], *cleanedJets[2]), weight);
          FILLx2(_histDeltaPhiJ1J2_3, is_boosted, deltaPhi(*cleanedJets[0], *cleanedJets[1]), weight);
          FILLx2(_histDeltaPhiJ1J3_3, is_boosted, deltaPhi(*cleanedJets[0], *cleanedJets[2]), weight);
          FILLx2(_histDeltaPhiJ2J3_3, is_boosted, deltaPhi(*cleanedJets[1], *cleanedJets[2]), weight);
        }
      }
    }


    /// Normalizations
    /// @note Most of these data normalizations neglect the overflow bins
    void finalize() {
      for (size_t i = 0; i < 2; ++i) {
        normalize(_histDeltaPhiZJ1_1[i], 1, false);
        normalize(_histDeltaPhiZJ1_2[i], 1, false);
        normalize(_histDeltaPhiZJ1_3[i], 1, false);
        normalize(_histDeltaPhiZJ2_3[i], 1, false);
        normalize(_histDeltaPhiZJ3_3[i], 1, false);
        normalize(_histDeltaPhiJ1J2_3[i], 1, false);
        normalize(_histDeltaPhiJ1J3_3[i], 1, false);
        normalize(_histDeltaPhiJ2J3_3[i], 1, false);
        normalize(_histTransvThrust[i]);
      }
    }


  private:


    // Define a helper to appropriately fill both unboosted and boosted histo versions
    void FILLx2(Histo1DPtr* HNAME, bool is_boosted, double VAL, double weight) { 
      double x = VAL; 
      for (size_t i = 0; i < 2; ++i) {
        if (i == 0 || is_boosted) 
          HNAME[i]->fill(x, weight); 
      }
    }



    // Arrays of unboosted/boosted histos
    Histo1DPtr _histDeltaPhiZJ1_1[2];
    Histo1DPtr _histDeltaPhiZJ1_2[2];
    Histo1DPtr _histDeltaPhiZJ1_3[2];
    Histo1DPtr _histDeltaPhiZJ2_3[2];
    Histo1DPtr _histDeltaPhiZJ3_3[2];
    Histo1DPtr _histDeltaPhiJ1J2_3[2];
    Histo1DPtr _histDeltaPhiJ1J3_3[2];
    Histo1DPtr _histDeltaPhiJ2J3_3[2];
    Histo1DPtr _histTransvThrust[2];

  };


  DECLARE_RIVET_PLUGIN(CMS_2013_I1209721);

}