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CDF_2008_I768579

Jet pT and multiplicity distributions in W + jets events
Experiment: CDF (Tevatron Run 2)
Inspire ID: 768579
Status: VALIDATED
Authors:
  • Ben Cooper
  • Emily Nurse
References: Beams: p- p+
Beam energies: (980.0, 980.0) GeV
Run details:
  • Requires the process $p\bar{p} \rightarrow {W} \rightarrow {e}\nu$. Additional hard jets will also have to be included to get a good description. The LO process in Herwig is set with IPROC=1451.

Measurement of the cross section for W boson production in association with jets in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV. The analysis uses 320 pb$^{-1}$ of data collected with the CDF II detector. W bosons are identified in their $e\nu$ decay channel and jets are reconstructed using an $R < 0.4$ cone algorithm. For each $W + \geq$ n-jet sample (where n = 1--4) a measurement of d$\sigma({p}\bar{p} \rightarrow W + \geq$ n jet)/d$E_T(n^{th}$-jet) $\times$ BR($W \rightarrow{e}\nu$) is made, where d$E_T(n^{th}$-jet) is the Et of the n$^{th}$-highest Et jet above 20 GeV. A measurement of the total cross section, $\sigma(p\bar{p} \rightarrow W + \geq$ $n$-jet) $\times$ BR($W \rightarrow{e}\nu)$ with $E_T(n^{th}-jet) > 25$ GeV is also made. Both measurements are made for jets with $|\eta| < 2$ and for a limited region of the $W \rightarrow{e}\nu$ decay phase space; $|\eta^{e}| < 1.1$, $p_{T}^{e} > 20$ GeV, $p_{T}^{\nu} > 30$ GeV and $M_{T} > 20$ GeV. The cross sections are corrected for all detector effects and can be directly compared to particle level $W$ + jet(s) predictions. These measurements can be used to test and tune QCD predictions for the number of jets in and kinematics of $W$ + jets events.

Source code: CDF_2008_I768579.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/VetoedFinalState.hh"
  5#include "Rivet/Projections/InvMassFinalState.hh"
  6#include "Rivet/Projections/FastJets.hh"
  7#include <algorithm>
  8
  9namespace Rivet {
 10
 11
 12  /// @brief CDF jet pT and multiplicity distributions in W + jets events
 13  ///
 14  /// This CDF analysis provides jet pT distributions for 4 jet multiplicity bins
 15  /// as well as the jet multiplicity distribution in W + jets events.
 16  class CDF_2008_I768579 : public Analysis {
 17  public:
 18
 19    RIVET_DEFAULT_ANALYSIS_CTOR(CDF_2008_I768579);
 20
 21
 22    /// @name Analysis methods
 23    /// @{
 24
 25    void init() {
 26      // Set up projections
 27      // Basic FS
 28      FinalState fs((Cuts::etaIn(-3.6, 3.6)));
 29      declare(fs, "FS");
 30
 31      // Create a final state with any e-nu pair with invariant mass 65 -> 95 GeV and ET > 20 (W decay products)
 32      vector<pair<PdgId,PdgId> > vids;
 33      vids += make_pair(PID::ELECTRON, PID::NU_EBAR);
 34      vids += make_pair(PID::POSITRON, PID::NU_E);
 35      FinalState fs2(Cuts::abseta < 3.6 && Cuts::pT >= 20*GeV);
 36      InvMassFinalState invfs(fs2, vids, 65*GeV, 95*GeV);
 37      declare(invfs, "INVFS");
 38
 39      // Make a final state without the W decay products for jet clustering
 40      VetoedFinalState vfs(fs);
 41      vfs.addVetoOnThisFinalState(invfs);
 42      declare(vfs, "VFS");
 43      declare(FastJets(vfs, JetAlg::CDFJETCLU, 0.4), "Jets");
 44
 45      // Book histograms
 46      for (int i = 0 ; i < 4 ; ++i) {
 47        book(_histJetEt[i], i+1, 1, 1);
 48        book(_histJetMultRatio[i], 5, 1, i+1);
 49        book(_histJetMult[i], i+6, 1, 1);
 50        book(_numer[i],"/TMP/numer"+std::to_string(i));
 51        book(_denom[i],"/TMP/denom"+std::to_string(i));
 52      }
 53
 54    }
 55
 56
 57    /// Do the analysis
 58    void analyze(const Event& event) {
 59      // Get the W decay products (electron and neutrino)
 60      const InvMassFinalState& invMassFinalState = apply<InvMassFinalState>(event, "INVFS");
 61      const Particles&  wDecayProducts = invMassFinalState.particles();
 62
 63      FourMomentum electronP, neutrinoP;
 64      bool gotElectron(false), gotNeutrino(false);
 65      for (const Particle& p : wDecayProducts) {
 66        FourMomentum p4 = p.momentum();
 67        if (p4.Et() > 20*GeV && p4.abseta() < 1.1 && p.abspid() == PID::ELECTRON) {
 68          electronP = p4;
 69          gotElectron = true;
 70        }
 71        else if (p4.Et() > 30*GeV && p.abspid() == PID::NU_E) {
 72          neutrinoP = p4;
 73          gotNeutrino = true;
 74        }
 75      }
 76
 77      // Veto event if the electron or MET cuts fail
 78      if (!gotElectron || !gotNeutrino) vetoEvent;
 79
 80      // Veto event if the MTR cut fails
 81      double mT2 = 2.0 * ( electronP.pT()*neutrinoP.pT() - electronP.px()*neutrinoP.px() - electronP.py()*neutrinoP.py() );
 82      if (sqrt(mT2) < 20*GeV ) vetoEvent;
 83
 84      // Get the jets
 85      const JetFinder& jetProj = apply<FastJets>(event, "Jets");
 86      Jets theJets = jetProj.jets(cmpMomByEt, Cuts::Et > 20*GeV);
 87      size_t njetsA(0), njetsB(0);
 88      for (const Jet& j : theJets) {
 89        if (j.absrap() < 2.0) {
 90          // Fill differential histograms for top 4 jets with Et > 20
 91          if (njetsA < 4 && j.Et() > 20*GeV) {
 92            ++njetsA;
 93            _histJetEt[njetsA-1]->fill(j.Et()/GeV);
 94          }
 95          // Count number of jets with Et > 25 (for multiplicity histograms)
 96          if (j.Et() > 25*GeV)  ++njetsB;
 97        }
 98      }
 99
100      // Increment event counter
101      _denom[0]->fill();
102
103      // Jet multiplicity
104      for (size_t i = 1; i <= njetsB; ++i) {
105        _histJetMult[i-1]->fill(1960);
106        _numer[i-1]->fill();
107        if (i == 4) break;
108        _denom[i]->fill();
109      }
110    }
111
112
113    /// Finalize
114    void finalize() {
115
116      // Loop over the non-zero multiplicities
117      for (size_t i = 0; i < 4; ++i) {
118        if (!_denom[i]->val())  continue;
119        const YODA::Estimate0D ratio = (*_numer[i]) / (*_denom[i]);
120        _histJetMultRatio[i]->bin(1).set(ratio.val(), ratio.err());
121      }
122
123      // Normalize the non-ratio histograms
124      for (size_t i = 0; i < 4; ++i) {
125        scale(_histJetEt[i], crossSection()/picobarn/sumOfWeights());
126        scale(_histJetMult[i], crossSection()/picobarn/sumOfWeights());
127      }
128
129    }
130
131    /// @}
132
133
134  private:
135
136    /// @name Histograms
137    /// @{
138    Histo1DPtr _histJetEt[4];
139    BinnedEstimatePtr<int> _histJetMultRatio[4];
140    BinnedHistoPtr<int> _histJetMult[4];
141    CounterPtr _numer[4], _denom[4];
142    /// @}
143
144  };
145
146
147
148  RIVET_DECLARE_ALIASED_PLUGIN(CDF_2008_I768579, CDF_2008_S7541902);
149
150}