Rivet analyses

title: 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: - arXiv: 0711.4044 - Phys.Rev.D77:011108,2008

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

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/InvMassFinalState.hh"

include "Rivet/Projections/VetoedFinalState.hh"

include

namespace Rivet {

/// @brief CDF jet pT and multiplicity distributions in W + jets events /// /// This CDF analysis provides jet pT distributions for 4 jet multiplicity bins /// as well as the jet multiplicity distribution in W + jets events. class CDF_2008_I768579 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(CDF_2008_I768579);


/// @name Analysis methods
/// @{

void init() {
  // Set up projections
  // Basic FS
  FinalState fs((Cuts::etaIn(-3.6, 3.6)));
  declare(fs, "FS");

  // Create a final state with any e-nu pair with invariant mass 65 -> 95 GeV and ET > 20 (W decay products)
  vector<pair<PdgId, PdgId>> vids;
  vids += make_pair(PID::ELECTRON, PID::NU_EBAR);
  vids += make_pair(PID::POSITRON, PID::NU_E);
  FinalState fs2(Cuts::abseta < 3.6 && Cuts::pT >= 20 * GeV);
  InvMassFinalState invfs(fs2, vids, 65 * GeV, 95 * GeV);
  declare(invfs, "INVFS");

  // Make a final state without the W decay products for jet clustering
  VetoedFinalState vfs(fs);
  vfs.addVetoOnThisFinalState(invfs);
  declare(vfs, "VFS");
  declare(FastJets(vfs, JetAlg::CDFJETCLU, 0.4), "Jets");

  // Book histograms
  for (int i = 0; i < 4; ++i) {
    book(_histJetEt[i], i + 1, 1, 1);
    book(_histJetMultRatio[i], 5, 1, i + 1);
    book(_histJetMult[i], i + 6, 1, 1);
    book(_numer[i], "/TMP/numer" + std::to_string(i));
    book(_denom[i], "/TMP/denom" + std::to_string(i));
  }
}


/// Do the analysis
void analyze(const Event& event) {
  // Get the W decay products (electron and neutrino)
  const InvMassFinalState& invMassFinalState = apply<InvMassFinalState>(event, "INVFS");
  const Particles& wDecayProducts = invMassFinalState.particles();

  FourMomentum electronP, neutrinoP;
  bool gotElectron(false), gotNeutrino(false);
  for (const Particle& p : wDecayProducts) {
    FourMomentum p4 = p.momentum();
    if (p4.Et() > 20 * GeV && p4.abseta() < 1.1 && p.abspid() == PID::ELECTRON) {
      electronP = p4;
      gotElectron = true;
    }
    else if (p4.Et() > 30 * GeV && p.abspid() == PID::NU_E) {
      neutrinoP = p4;
      gotNeutrino = true;
    }
  }

  // Veto event if the electron or MET cuts fail
  if (!gotElectron || !gotNeutrino) vetoEvent;

  // Veto event if the MTR cut fails
  double mT2 = 2.0
      * (electronP.pT() * neutrinoP.pT() - electronP.px() * neutrinoP.px()
         - electronP.py() * neutrinoP.py());
  if (sqrt(mT2) < 20 * GeV) vetoEvent;

  // Get the jets
  const JetFinder& jetProj = apply<FastJets>(event, "Jets");
  Jets theJets = jetProj.jets(cmpMomByEt, Cuts::Et > 20 * GeV);
  size_t njetsA(0), njetsB(0);
  for (const Jet& j : theJets) {
    if (j.absrap() < 2.0) {
      // Fill differential histograms for top 4 jets with Et > 20
      if (njetsA < 4 && j.Et() > 20 * GeV) {
        ++njetsA;
        _histJetEt[njetsA - 1]->fill(j.Et() / GeV);
      }
      // Count number of jets with Et > 25 (for multiplicity histograms)
      if (j.Et() > 25 * GeV) ++njetsB;
    }
  }

  // Increment event counter
  _denom[0]->fill();

  // Jet multiplicity
  for (size_t i = 1; i <= njetsB; ++i) {
    _histJetMult[i - 1]->fill(1960);
    _numer[i - 1]->fill();
    if (i == 4) break;
    _denom[i]->fill();
  }
}


/// Finalize
void finalize() {

  // Loop over the non-zero multiplicities
  for (size_t i = 0; i < 4; ++i) {
    if (!_denom[i]->val()) continue;
    const YODA::Estimate0D ratio = (*_numer[i]) / (*_denom[i]);
    _histJetMultRatio[i]->bin(1).set(ratio.val(), ratio.err());
  }

  // Normalize the non-ratio histograms
  for (size_t i = 0; i < 4; ++i) {
    scale(_histJetEt[i], crossSection() / picobarn / sumOfWeights());
    scale(_histJetMult[i], crossSection() / picobarn / sumOfWeights());
  }
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _histJetEt[4];
BinnedEstimatePtr<int> _histJetMultRatio[4];
BinnedHistoPtr<int> _histJetMult[4];
CounterPtr _numer[4], _denom[4];
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(CDF_2008_I768579, CDF_2008_S7541902);

} ```

Aliases: - CDF_2008_S7541902