Rivet analyses

title: LHCB_2010_I867355

Measurement of $\sigma(pp \to b \bar{b} X$ at $\sqrt{s} = 7$ TeV in the forward region

Experiment: LHCb (LHC)

Inspire ID: 867355

Status: VALIDATED

Authors: - Andy Buckley - Sercan Sen - Peter Skands - Sheldon Stone

References: - arXiv: 1009.2731

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - $pp$ to $b$-hadron + $X$ at 7 TeV. i.e., switch on "HardQCD:gg2bbbar" and "HardQCD:qqbar2bbbar" flags in Pythia8.

The average cross-section to produce $b$-flavoured or $\bar{b}$-flavoured hadrons is measured in different pseudorapidity intervals over the entire range of \pT, assuming the LEP (and Tevatron) fractions for fragmentation into $b$-flavoured hadrons.

Source code:LHCB_2010_I867355.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Particle.hh"

namespace Rivet {

class LHCB_2010_I867355 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2010_I867355);


void init() {

  /// @note Results are presented for two different fragmentation
  /// functions, LEP and Tevatron, therefore two sets of histos.
  book(_h_sigma_vs_eta_lep, 1, 1, 1);
  book(_h_sigma_vs_eta_tvt, 1, 1, 2);
  book(_h_sigma_total_lep, 2, 1, 1);
  book(_h_sigma_total_tvt, 2, 1, 2);
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles bhadrons;
  for (ConstGenParticlePtr p : HepMCUtils::particles(event.genEvent())) {
    if (!(PID::isHadron(p->pdg_id()) && PID::hasBottom(p->pdg_id()))) continue;

    ConstGenVertexPtr dv = p->end_vertex();

    bool hasBdaughter = false;
    if (PID::isHadron(p->pdg_id()) && PID::hasBottom(p->pdg_id())) { // selecting b-hadrons
      if (dv) {
        for (ConstGenParticlePtr pp : HepMCUtils::particles(dv, Relatives::CHILDREN)) {
          if (PID::isHadron(pp->pdg_id()) && PID::hasBottom(pp->pdg_id())) {
            hasBdaughter = true;
          }
        }
      }
    }
    if (hasBdaughter) continue; // continue if the daughter is another b-hadron

    bhadrons += Particle(*p);
  }

  for (const Particle& particle : bhadrons) {

    // take fabs() to use full statistics and then multiply weight by 0.5 because LHCb is single-sided
    double eta = fabs(particle.eta());

    _h_sigma_vs_eta_lep->fill(eta, 0.5);
    _h_sigma_vs_eta_tvt->fill(eta, 0.5);

    _h_sigma_total_lep->fill(eta, 0.5); // histogram for full kinematic range
    _h_sigma_total_tvt->fill(eta, 0.5); // histogram for full kinematic range
  }
}


void finalize() {
  double norm = crossSection() / microbarn / sumOfWeights();
  double binwidth = 4.; // integrated over full rapidity space from 2 to 6.

  // to get the avergae of b and bbar, we scale with 0.5
  scale(_h_sigma_vs_eta_lep, 0.5 * norm);
  scale(_h_sigma_vs_eta_tvt, 0.5 * norm);
  scale(_h_sigma_total_lep, 0.5 * norm * binwidth);
  scale(_h_sigma_total_tvt, 0.5 * norm * binwidth);
}

private:

Histo1DPtr _h_sigma_total_lep;
Histo1DPtr _h_sigma_total_tvt;
Histo1DPtr _h_sigma_vs_eta_lep;
Histo1DPtr _h_sigma_vs_eta_tvt;

};

RIVET_DECLARE_PLUGIN(LHCB_2010_I867355);

} ```