rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

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:
  • 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 p_\perp 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
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.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(-4.7, 4.7);
      declare(FastJets(cnfs, FastJets::ANTIKT, 0.5), "Jets");

      _h_jetetas[0]     = bookHisto1D(1,1,1);
      _h_jetpts[0]      = bookHisto1D(2,1,1);
      _h_DeltaS         = bookHisto1D(3,1,1);
      _h_DeltaPhiSoft   = bookHisto1D(4,1,1);
      _h_DeltaPtRelSoft = bookHisto1D(5,1,1);
      _h_jetetas[2]     = bookHisto1D(6,1,1);
      _h_jetpts[2]      = bookHisto1D(7,1,1);
      _h_jetetas[3]     = bookHisto1D(8,1,1);
      _h_jetpts[3]      = bookHisto1D(9,1,1);
      _h_jetetas[1]     = bookHisto1D(10,1,1);
      _h_jetpts[1]      = bookHisto1D(11,1,1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      /// @todo Use jetsByPt(ptGtr(20*GeV) & absetaIn(4.7)), then no need for the lower loop;
      const Jets jets = apply<FastJets>(event, "Jets").jetsByPt(20*GeV);
      if (jets.size() < 4) vetoEvent;

      // Ensure that there are exactly 4 jets > 20 GeV, with two above 50 GeV
      Jets hardjets, alljets;
      foreach (const Jet& j, jets) {
        if (j.abseta() > 4.7) continue;
        if (j.pT() > 50*GeV) hardjets.push_back(j);
        if (j.pT() > 20*GeV) alljets.push_back(j);
      }
      if (hardjets.size() < 2 || alljets.size() != 4) vetoEvent;
      const double weight = event.weight();

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

      // 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, weight);

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

      // 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, weight);
    }


    /// 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;

  };


  DECLARE_RIVET_PLUGIN(CMS_2013_I1273574);

}