Rivet analyses

title: ATLAS_2012_I1082936

Inclusive jet and dijet cross sections at 7 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1082936

Status: VALIDATED

Authors: - Holger Schulz

References: - arXiv: 1112.6297v2 - CERN-PH-EP-2011-192

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - QCD jet production with a minimum leading jet pT of 30 GeV and minimum second jet pT of 20 GeV at 7 TeV.

Inclusive jet and dijet cross sections have been measured in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector at the Large Hadron Collider. The cross sections were measured using jets clustered with the anti-kT algorithm with parameters R=0.4 and R=0.6. These measurements are based on the 2010 data sample, consisting of a total integrated luminosity of 37 inverse picobarns. Inclusive jet double-differential cross sections are presented as a function of jet transverse momentum, in bins of jet rapidity. Dijet double-differential cross sections are studied as a function of the dijet invariant mass, in bins of half the rapidity separation of the two leading jets. The measurements are performed in the jet rapidity range $|y|<4.4$, covering jet transverse momenta from 20 GeV to 1.5 TeV and dijet invariant masses from 70 GeV to 5 TeV. This is the successor analysis of ATLAS_2010_S8817804

Source code:`ATLAS_2012_I1082936.cc`

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

class ATLAS_2012_I1082936 : public Analysis { public:

/// @name Constructors etc.
/// @{

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2012_I1082936);

/// @}

public:

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

/// Book histograms and initialise projections before the run
void init() {

  const FinalState fs;
  declare(fs, "FinalState");

  FastJets fj04(fs, JetAlg::ANTIKT, 0.4);
  fj04.useInvisibles();
  declare(fj04, "AntiKT04");

  FastJets fj06(fs, JetAlg::ANTIKT, 0.6);
  fj06.useInvisibles();
  declare(fj06, "AntiKT06");


  // Histogram booking copied from the previous analysis
  const vector<double> ybins{0.0, 0.3, 0.8, 1.2, 2.1, 2.8, 3.6, 4.4};
  const vector<double> ystarbins{0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.4};

  size_t ptDsOffset(0), massDsOffset(2);
  for (size_t alg = 0; alg < 2; ++alg) {
    book(_pThistos[alg], ybins);
    for (auto& b : _pThistos[alg]->bins()) {
      book(b, 1 + ptDsOffset, 1, b.index());
    }
    ++ptDsOffset;

    book(_mass[alg], ystarbins);
    for (auto& b : _mass[alg]->bins()) {
      book(b, 1 + massDsOffset, 1, b.index());
    }
    ++massDsOffset;
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {

  Jets jetAr[2];
  jetAr[AKT6] = apply<FastJets>(event, "AntiKT06").jetsByPt(Cuts::pT > 20 * GeV);
  jetAr[AKT4] = apply<FastJets>(event, "AntiKT04").jetsByPt(Cuts::pT > 20 * GeV);

  // Loop over jet "radii" used in analysis
  for (size_t alg = 0; alg < 2; ++alg) {
    // Identify dijets
    vector<FourMomentum> leadjets;
    for (const Jet& jet : jetAr[alg]) {
      const double pT = jet.pT();
      const double absy = jet.absrap();
      _pThistos[alg]->fill(absy, pT / GeV);

      if (absy < 4.4 && leadjets.size() < 2) {
        if (leadjets.empty() && pT < 30 * GeV) continue;
        leadjets.push_back(jet.momentum());
      }
    }
    // Make sure we have a leading jet with pT >30 GeV and a second to leading jet with pT>20 GeV
    if (leadjets.size() < 2) {
      MSG_DEBUG("Could not find two suitable leading jets");
      continue;
    }

    const double y1 = leadjets[0].rapidity();
    const double y2 = leadjets[1].rapidity();
    const double ystar = fabs(y1 - y2) / 2.;
    const double m = (leadjets[0] + leadjets[1]).mass();
    // Fill mass histogram
    _mass[alg]->fill(ystar, m / TeV);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // factor 0.5 needed because it is differential in dy and not d|y|
  scale(_pThistos, 0.5 * crossSectionPerEvent() / picobarn);
  scale(_mass, crossSectionPerEvent() / picobarn);
  divByGroupWidth(_pThistos);
  divByGroupWidth(_mass);
}

/// @}

private:

// Data members like post-cuts event weight counters go here

enum Alg { AKT4 = 0, AKT6 = 1 };