Rivet analyses

title: ATLAS_2010_I871366

Inclusive jet cross section and di-jet mass and chi spectra at 7 TeV in ATLAS

Experiment: ATLAS (LHC 7TeV)

Inspire ID: 871366

Status: VALIDATED

Authors: - James Monk

References: - Expt page: ATLAS-STDM-2010-03 - arXiv: 1009.5908

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - pp QCD jet production with a minimum jet pT of 60 GeV (inclusive) or 30 GeV (di-jets) at 7 TeV.

The first jet cross section measurement made with the ATLAS detector at the LHC. Anti-kt jets with $R=0.4$ and $R=0.6$ are resconstructed within $|y|<2.8$ and above 60~GeV for the inclusive jet cross section plots. For the di-jet plots the second jet must have pT>30~GeV. Jet pT and di-jet mass spectra are plotted in bins of rapidity between $|y| = $ 0.3, 0.8, 1.2, 2.1, and 2.8. Di-jet $\chi$ spectra are plotted in bins of di-jet mass between 340 GeV, 520 GeV, 800 GeV and 1200 GeV.

Source code:ATLAS_2010_I871366.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

namespace Rivet {

/// @brief ATLAS inclusive jet pT spectrum, di-jet Mass and di-jet chi class ATLAS_2010_I871366 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2010_I871366);

/// Choice of jet algorithm
enum Alg { AKT4 = 0, AKT6 = 1 };


void init() {
  FinalState fs;
  declare(fs, "FinalState");
  declare(FastJets(fs, JetAlg::ANTIKT, 0.6), "AntiKT06");
  declare(FastJets(fs, JetAlg::ANTIKT, 0.4), "AntiKT04");

  const vector<double> ybins{0.0, 0.3, 0.8, 1.2, 2.1, 2.8};
  const vector<double> massBinsForChi{340, 520, 800, 1200};


  size_t ptDsOffset(0), massDsOffset(10), chiDsOffset(20);
  for (size_t alg = 0; alg < 2; ++alg) {
    book(_pThistos[alg], ybins);
    for (auto& b : _pThistos[alg]->bins()) {
      book(b, b.index() + ptDsOffset, 1, 1);
    }
    ptDsOffset += 5;

    book(_massVsY[alg], ybins);
    for (auto& b : _massVsY[alg]->bins()) {
      book(b, b.index() + massDsOffset, 1, 1);
    }
    massDsOffset += 5;

    book(_chiVsMass[alg], massBinsForChi);
    for (auto& b : _chiVsMass[alg]->bins()) {
      book(b, b.index() + chiDsOffset, 1, 1);
    }
    chiDsOffset += 3;
  }
}


void analyze(const Event& evt) {
  Jets jetAr[2];
  jetAr[AKT6] = apply<FastJets>(evt, "AntiKT06").jetsByPt(Cuts::pT > 30 * GeV);
  jetAr[AKT4] = apply<FastJets>(evt, "AntiKT04").jetsByPt(Cuts::pT > 30 * GeV);

  // Identify the dijets
  for (size_t alg = 0; alg < 2; ++alg) {
    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 < 2.8 && leadjets.size() < 2) {
        if (leadjets.empty() && pT < 60 * GeV) continue;
        leadjets.push_back(jet.momentum());
      }
    }

    // Veto if no acceptable dijet found
    if (leadjets.size() < 2) {
      MSG_DEBUG("Could not find two suitable leading jets");
      continue;
    }

    const double rap1 = leadjets[0].rapidity();
    const double rap2 = leadjets[1].rapidity();
    const double mass = (leadjets[0] + leadjets[1]).mass();
    const double ymax = max(fabs(rap1), fabs(rap2));
    const double chi = exp(fabs(rap1 - rap2));
    if (fabs(rap1 + rap2) < 2.2) {
      _chiVsMass[alg]->fill(mass / GeV, chi);
    }
    _massVsY[alg]->fill(ymax, mass / GeV);
  }
}


void finalize() {
  const double sf = crossSectionPerEvent() / picobarn;
  // factor 0.5 needed because it is differential in dy and not d|y|
  scale(_pThistos, 0.5 * sf);
  scale(_massVsY, sf);
  scale(_chiVsMass, sf);

  divByGroupWidth(_pThistos);
  divByGroupWidth(_massVsY);
  divByGroupWidth(_chiVsMass);
}

private:

/// The inclusive pT spectrum for akt6 and akt4 jets (array index is jet type from enum above)
Histo1DGroupPtr _pThistos[2];

/// The di-jet mass spectrum binned in rapidity for akt6 and akt4 jets (array index is jet type from enum above)
Histo1DGroupPtr _massVsY[2];

/// The di-jet chi distribution binned in mass for akt6 and akt4 jets (array index is jet type from enum above)
Histo1DGroupPtr _chiVsMass[2];

};

RIVET_DECLARE_ALIASED_PLUGIN(ATLAS_2010_I871366, ATLAS_2010_S8817804);

} ```

Aliases: - ATLAS_2010_S8817804