Rivet analyses

title: CMS_2013_I1273574

Studies of 4-jet production in proton-proton collisions at $\sqrt{s} = 7$ TeV

Experiment: CMS (LHC)

Inspire ID: 1273574

Status: VALIDATED

Authors: - P. Gunnellini - A. Buckley

References: - Expt page: CMS-FSQ-12-013 - CERN-PH-EP-2013-229 - arXiv: 1312.6440 - Submitted to Phys. Rev. D

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - Hard QCD events with \pT cut at generator level of 45 GeV

Measurements are presented of exclusive 4-jet production cross sections as a function of the transverse momentum $p_T$, pseudorapidity $\eta$, as well as of correlations in azimuthal angle and $p_T$ balance among the jets. The data sample was collected at a centre-of-mass energy of 7 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 36 pb$^{-1}$. The jets are reconstructed with the anti-$k_T$ jet algorithm in a range of $|\eta|<4.7$.

Source code:CMS_2013_I1273574.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// CMS 4-jet production at 7 TeV class CMS_2013_I1273574 : public Analysis { public:

/// Constructor
CMS_2013_I1273574()
    : Analysis("CMS_2013_I1273574") { }


/// Book histograms and initialise projections before the run
void init() {
  const FinalState cnfs((Cuts::etaIn(-4.7, 4.7)));
  declare(FastJets(cnfs, JetAlg::ANTIKT, 0.5), "Jets");

  // Modified to match the HEPDATA record.
  // eta of highest pT jet
  //book(_h_jetetas[0]     ,1,1,1);
  book(_h_jetetas[0], 6, 1, 1);

  // pt of the highest pT jet
  book(_h_jetpts[0], 2, 1, 1);

  //book(_h_DeltaS         ,3,1,1);
  book(_h_DeltaS, 12, 1, 1);

  //book(_h_DeltaPhiSoft   ,4,1,1);
  book(_h_DeltaPhiSoft, 10, 1, 1);

  //book(_h_DeltaPtRelSoft ,5,1,1);
  book(_h_DeltaPtRelSoft, 11, 1, 1);

  // eta and pT of 3rd highest pT jet
  //book(_h_jetetas[2]     ,6,1,1);
  //book(_h_jetpts[2]      ,7,1,1);
  book(_h_jetetas[2], 8, 1, 1);
  book(_h_jetpts[2], 4, 1, 1);

  // eta and pT of 4th highest pT jet
  //book(_h_jetetas[3]     ,8,1,1);
  //book(_h_jetpts[3]      ,9,1,1);
  book(_h_jetetas[3], 9, 1, 1);
  book(_h_jetpts[3], 5, 1, 1);

  // eta and pT of 2nd highest pT jet
  //book(_h_jetetas[1]     ,10,1,1);
  //book(_h_jetpts[1]      ,11,1,1);
  book(_h_jetetas[1], 7, 1, 1);
  book(_h_jetpts[1], 3, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const Jets jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 20 * GeV && Cuts::abseta < 4.7);
  if (jets.size() < 4) vetoEvent;

  // Ensure that there are exactly 4 jets > 20 GeV, with two above 50 GeV
  Jets hardjets, alljets;
  for (const Jet& j : jets) {
    if (j.pT() > 50 * GeV) hardjets.push_back(j);
    alljets.push_back(j);
  }
  if (hardjets.size() < 2 || alljets.size() != 4) vetoEvent;

  // Histogram pT and eta of all 4 jets
  for (size_t i = 0; i < 4; ++i) {
    _h_jetpts[i]->fill(alljets[i].pT() / GeV);
    _h_jetetas[i]->fill(alljets[i].eta());
  }

  // Create vector sums of the hard and soft pairs of jets
  const FourMomentum p12 = alljets[0].momentum() + alljets[1].momentum();
  const FourMomentum p34 = alljets[2].momentum() + alljets[3].momentum();

  // Fill the delta(phi) between the soft jets
  const double dphisoft = deltaPhi(alljets[2], alljets[3]);
  _h_DeltaPhiSoft->fill(dphisoft);

  // Fill the pT balance between the soft jets
  const double ptbalanceSoft = p34.pT() / (alljets[2].pT() + alljets[3].pT());
  _h_DeltaPtRelSoft->fill(ptbalanceSoft);

  // Fill the azimuthal angle difference between the two jet pairs
  const double p12p34_trans = p12.px() * p34.px() + p12.py() * p34.py();
  const double DeltaS = acos(p12p34_trans / p12.pT() / p34.pT());
  _h_DeltaS->fill(DeltaS);
}


/// Normalise histograms (mostly to cross-section)
void finalize() {
  const double invlumi = crossSection() / picobarn / sumOfWeights();
  for (size_t i = 0; i < 4; ++i) {
    scale(_h_jetpts[i], invlumi);
    scale(_h_jetetas[i], invlumi);
  }
  normalize(_h_DeltaPtRelSoft);
  normalize(_h_DeltaPhiSoft);
  normalize(_h_DeltaS);
}

private:

Histo1DPtr _h_jetpts[4], _h_jetetas[4];
Histo1DPtr _h_DeltaS, _h_DeltaPhiSoft, _h_DeltaPtRelSoft;

};

RIVET_DECLARE_PLUGIN(CMS_2013_I1273574);

} ```