Rivet analyses

title: ATLAS_2014_I1326641

3-jet cross section with 7 TeV data

Experiment: ATLAS (LHC)

Inspire ID: 1326641

Status: VALIDATED

Authors: - Aliaksei Hrynevich - Pavel Starovoitov

References: - Expt page: ATLAS-STDM-2013-09 - arXiv: 1411.1855 - DOI: 10.1140/epjc/s10052-015-3363-3 - Eur.Phys.J. C75 (2015) 228

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - QCD jet production with at least three leading jets

Double-differential three-jet production cross-sections have been measured in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 7\,$TeV using the ATLAS detector at the Large Hadron Collider. The measurements are presented as a function of the three-jet mass ($m_{jjj}$), in bins of the sum of the absolute rapidity separations between the three leading jets ($\left|Y^\ast\right|$). Invariant masses extending up to 5\,TeV are reached for $8<\left|Y^\ast\right|<10$. These measurements use a sample of data recorded using the ATLAS detector in 2011, which corresponds to an integrated luminosity of $4.51\,\text{fb}^{-1}$. Jets are identified using the anti-$k_\text{t}$ algorithm with two different jet radius parameters, $R=0.4$ and $R=0.6$.

Source code:`ATLAS_2014_I1326641.cc`

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

class ATLAS_2014_I1326641 : public Analysis { public:

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

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2014_I1326641);

/// @}


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

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

  const FinalState fs;

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

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

  const vector<double> ystarBins{0.0, 2.0, 4.0, 6.0, 8.0, 10.0};

  size_t massDsOffset(0);
  for (size_t alg = 0; alg < 2; ++alg) {
    book(h_trijet_Mass[alg], ystarBins);
    for (auto& b : h_trijet_Mass[alg]->bins()) {
      book(b, 1 + massDsOffset, 1, 1);
      ++massDsOffset;
    }
  }
}

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

  Jets jetAr[2];
  jetAr[AKT4] = apply<FastJets>(event, "AntiKT04").jetsByPt(Cuts::pT > 50 * GeV);
  jetAr[AKT6] = apply<FastJets>(event, "AntiKT06").jetsByPt(Cuts::pT > 50 * GeV);

  const size_t nJets = 3;
  double ptCut[nJets] = {150., 100., 50.};

  // Loop over jet "radii" used in analysis
  for (size_t alg = 0; alg < 2; ++alg) {
    // Identify 3jets
    vector<FourMomentum> leadJets;
    for (const Jet& jet : jetAr[alg]) {
      if (jet.absrap() < 3.0 && leadJets.size() < nJets) {
        int filledJets = leadJets.size();
        if (jet.pT() < ptCut[filledJets]) continue;
        leadJets.push_back(jet.momentum());
      }
    }

    if (leadJets.size() < nJets) {
      MSG_DEBUG("Could not find three suitable leading jets");
      continue;
    }

    const double y1 = leadJets[0].rapidity();
    const double y2 = leadJets[1].rapidity();
    const double y3 = leadJets[2].rapidity();

    const double yStar = fabs(y1 - y2) + fabs(y2 - y3) + fabs(y1 - y3);
    const double m = (leadJets[0] + leadJets[1] + leadJets[2]).mass();
    h_trijet_Mass[alg]->fill(yStar, m);
  }
}


/// Normalise histograms etc., after the run
void finalize() {

  const double sf(2.0 * crossSection() / picobarn / sumOfWeights());
  scale(h_trijet_Mass, sf);
}

/// @}

private:

// Data members like post-cuts event weight counters go here
enum Alg { AKT4 = 0, AKT6 = 1 };