Rivet analyses

title: D0_2000_I499943

The $b\bar{b}$ production cross-section and angular correlations

Experiment: D0 (Tevatron Run 1)

Inspire ID: 499943

Status: VALIDATED

Authors: - Simone Amoroso

References: - Phys.Lett.B487:264-272,2000 - DOI: 10.1016/PhysLettB.487.264 - arXiv: hep-ex/9905024

Beams: p- p+

Beam energies: (900.0, 900.0)GeV

Run details: - $p\bar{p}$ dijet events at 1.8~\TeV, with a minimum \pt of 12~GeV.

Measurements of the $b\bar{b}$ production cross-section and angular correlations using the D0 detector at the Fermilab Tevatron $p\bar{p}$ collider operating at $\sqrt{s} = 1.8~\TeV$. The $b$ quark production cross-section and the angular correlations between $b$-quark pairs, for $|y(b)| < 1.0$ and $p_T(b) > 6~\GeV/c$, are extracted from single muon and dimuon data samples.

Source code:D0_2000_I499943.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/HeavyHadrons.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

namespace Rivet {

class D0_2000_I499943 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(D0_2000_I499943);


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

/// Book histograms and initialise projections before the run
void init() {
  FinalState fs;
  IdentifiedFinalState muons(Cuts::abseta < 0.8 && Cuts::pT > 4.0 * GeV);
  muons.acceptIdPair(PID::MUON);
  declare(muons, "Muons");

  FastJets jetproj(fs, JetAlg::D0ILCONE, 0.7);
  jetproj.useInvisibles();
  declare(jetproj, "Jets");

  // Book histograms
  book(_h_pt_leading_mu, 1, 1, 1);
  book(_h_dphi_mumu, 3, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const Jets& jets = apply<FastJets>(event, "Jets").jetsByPt(Cuts::pT > 12 * GeV);
  if (jets.size() < 2) vetoEvent;

  const Particles& muons = apply<IdentifiedFinalState>(event, "Muons").particlesByPt();
  if (muons.size() < 2) vetoEvent;

  // Muon selection: require the muons to be *close* to jets, not the usual overlap vetoing!
  Particles cand_mu;
  for (const Particle& mu : muons) {
    // Ignore muons in "bad" region 80 < phi < 110 degrees
    /// @todo Is this really not corrected for?!
    if (inRange(mu.phi(), 1.4, 1.92)) continue;

    // A muon is a good candidate if within R = 0.8 of a jet
    for (const Jet& jet : jets) {
      if (deltaR(mu, jet) < 0.8) {
        cand_mu.push_back(mu);
        break;
      }
    }
  }

  // Must find at least two jet-matched muons in the event
  if (cand_mu.size() < 2) vetoEvent;

  /// @todo Is this cut needed? Does space angle mean dR or 3D opening angle in lab frame?
  // Remove muon pairs closer than 165 deg in space angle (cosmic veto)
  // double dR_mumu = deltaR(cand_mu[0].momentum(), cand_mu[1].momentum());
  // if (dR_mumu < 165*degree) vetoEvent;

  // Selecting muon pairs with 6 < mass < 35 GeV (we use the two with highest pT)
  double m_mumu = (cand_mu[0].momentum() + cand_mu[1].momentum()).mass();
  if (!inRange(m_mumu, 6 * GeV, 35 * GeV)) vetoEvent;

  // Get phi angle between muons in degrees
  double dphi_mumu = deltaPhi(cand_mu[0], cand_mu[1]) * 180 / M_PI;

  // Fill histos
  _h_pt_leading_mu->fill(cand_mu[0].pt() / GeV);
  _h_dphi_mumu->fill(dphi_mumu);
}


// Normalise histograms to cross-section
void finalize() {
  scale(_h_pt_leading_mu, crossSection() / sumOfWeights() / nanobarn);
  scale(_h_dphi_mumu, crossSection() / sumOfWeights() / nanobarn);
}

/// @}

private:

/// @name Histograms
/// @{
Histo1DPtr _h_pt_leading_mu, _h_dphi_mumu;
/// @}

};

RIVET_DECLARE_PLUGIN(D0_2000_I499943);

} ```