Rivet analyses

title: ATLAS_2016_I1478355

Measurement of the bbar dijet dijet cross section at 7 TeV

Experiment: ATLAS (LHC)

Inspire ID: 1478355

Status: VALIDATED

Authors: - Lucia Keszeghova - Deepak Kar

References: - Expt page: ATLAS-STDM-2013-03 - Eur.Phys.J. C76 (2016) 670 - DOI:10.1140/epjc/s10052-016-4521-y - arXiv: 1607.08430

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - Dijet production, high pThatmin

The dijet production cross section for jets containing a $b$-hadron ($b$-jets) has been measured in proton-proton collisions with a centre-of-mass energy of $\sqrt{s} = 7$ TeV, using the ATLAS detector at the LHC. The data used correspond to an integrated luminosity of 4.2 fb$^{-1}$. The cross section is measured for events with two identified $b$-jets with a transverse momentum $p_\mathrm{T} > 20$GeV and a minimum separation in the $\eta$-$\phi$ plane of $\Delta R$ = 0.4. At least one of the jets in the event is required to have $p_\mathrm{T} > 270$GeV. The cross section is measured differentially as a function of dijet invariant mass, dijet transverse momentum, boost of the dijet system, and the rapidity difference, azimuthal angle and angular distance between the $b$-jets. The results are compared to different predictions of leading order and next-to-leading order perturbative quantum chromodynamics matrix elements supplemented with models for parton-showers and hadronization.

Source code:ATLAS_2016_I1478355.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/HeavyHadrons.hh"

namespace Rivet {

/// @brief Measurement of the bbar dijet dijet cross section at 7 TeV class ATLAS_2016_I1478355 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2016_I1478355);

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

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

  // Initialise and register projections
  FinalState fs(Cuts::abseta < 3.2);
  FastJets fj(fs, JetAlg::ANTIKT, 0.4);
  fj.useInvisibles();
  declare(fj, "Jets");
  declare(HeavyHadrons(Cuts::abseta < 3.2 && Cuts::pT > 5 * GeV), "BHadrons");

  book(_h["m_bb"], 1, 1, 1);
  book(_h["Delta_phi"], 2, 1, 1);
  book(_h["y_diff"], 3, 1, 1);
  book(_h["Delta_R"], 4, 1, 1);
  book(_h["pT_bb"], 5, 1, 1);
  book(_h["y_B"], 6, 1, 1);
}


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

  // Retrieve clustered jets, sorted by pT, with a minimum pT cut
  const Jets& jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 20 * GeV);
  const Particles& bHadrons = apply<HeavyHadrons>(event, "BHadrons").bHadrons();

  if (jets.size() < 1) vetoEvent;
  if (jets[0].pT() > 270 * GeV) {

    Jets foundBjets;
    for (const Jet& j : jets) {
      for (const Particle& b : bHadrons) {
        if ((deltaR(j, b) < 0.3) && (j.pT() > 20 * GeV) && (fabs(j.eta()) < 2.5)) foundBjets.push_back(j);
      }
    }

    Jet firstBjet;
    Jet secondBjet;
    bool bJetPair = false;
    for (const Jet& b1 : foundBjets) {
      for (const Jet& b2 : foundBjets) {
        if (deltaR(b1, b2) > 0.4) {
          bJetPair = true;
          firstBjet = b1;
          secondBjet = b2;
          break;
        }
      }
      if (bJetPair) break;
    }

    if (bJetPair) {
      const double mass = (firstBjet.momentum() + secondBjet.momentum()).mass();
      _h["m_bb"]->fill(mass / GeV);
      const double Delta_phi = deltaPhi(firstBjet.phi(), secondBjet.phi());
      _h["Delta_phi"]->fill(Delta_phi);
      const double y_diff = fabs(firstBjet.rapidity() - secondBjet.rapidity()) / 2;
      _h["y_diff"]->fill(y_diff);
      const double Delta_R = deltaR(firstBjet.momentum(), secondBjet.momentum());
      _h["Delta_R"]->fill(Delta_R);
      const double pT = (firstBjet.momentum() + secondBjet.momentum()).pT();
      _h["pT_bb"]->fill(pT / GeV);
      const double y_B = (firstBjet.rapidity() + secondBjet.rapidity()) / 2;
      _h["y_B"]->fill(y_B);
    }
  }
}

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

  const double xsec = crossSectionPerEvent() / picobarn;
  scale(_h, xsec);
}

///@}

/// @name Histograms
///@{
map<string, Histo1DPtr> _h;
///@}

};

RIVET_DECLARE_PLUGIN(ATLAS_2016_I1478355); } ```