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CMS_2011_S9088458

Measurement of ratio of the 3-jet over 2-jet cross section in $pp$ collisions at $\sqrt{s} = 7$ TeV
Experiment: CMS (LHC)
Inspire ID: 912560
Status: VALIDATED
Authors:
  • Tomo Umer
References:
  • Phys. Lett. B 702 (2011) 336
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Inclusive QCD at 7 TeV. $\hat{p_\perp}$ (or equivalent) greater than 30 GeV

A measurement of the ratio of the inclusive 3-jet to 2-jet cross sections as a function of the total jet transverse momentum, $H_T$, in the range $0.2 < H_T < 2.5$ TeV is presented. The data have been collected at a proton--proton centre-of-mass energy of 7\;TeV with the CMS detector at the LHC, and correspond to an integrated luminosity of 36/pb. Jets are anti-$k_t$ with $R = 0.5$, $p_\perp > 50\;\text{GeV}$ and $|\eta| < 2.5$.

Source code: CMS_2011_S9088458.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Tools/BinnedHistogram.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {


   /// CMS ratio of 3-jet to 2-jet cross-sections
   class CMS_2011_S9088458 : public Analysis {
   public:


     CMS_2011_S9088458()
       : Analysis("CMS_2011_S9088458") {  }


     void init() {
       FinalState fs;
       FastJets akt(fs, FastJets::ANTIKT, 0.5);
       declare(akt, "antikT");

       _h_tmp_dijet = Histo1D(refData(1, 1, 1));
       _h_tmp_trijet = Histo1D(refData(1, 1, 1));
       _h_r32 = bookScatter2D(1, 1, 1);
     }


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

       Jets highpT_jets;
       double HT = 0;
       foreach(const Jet & jet, apply<JetAlg>(event, "antikT").jetsByPt(50.0*GeV)) {
         if (jet.abseta() < 2.5) {
           highpT_jets.push_back(jet);
           HT += jet.pT();
         }
       }
       if (highpT_jets.size() < 2) vetoEvent;
       if (highpT_jets.size() >= 2) _h_tmp_dijet.fill(HT/TeV, weight);
       if (highpT_jets.size() >= 3) _h_tmp_trijet.fill(HT/TeV, weight);
     }


     void finalize() {
       divide(_h_tmp_trijet, _h_tmp_dijet, _h_r32);
     }


   private:

     Histo1D _h_tmp_dijet, _h_tmp_trijet;
     Scatter2DPtr _h_r32;

  };


  // A hook for the plugin system
  DECLARE_RIVET_PLUGIN(CMS_2011_S9088458);

}