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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: 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 p_\perp, assuming the LEP (and Tevatron) fractions for fragmentation into $b$-flavoured hadrons.

Source code: LHCB_2010_I867355.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Particle.hh"


namespace Rivet {

  class LHCB_2010_I867355 : public Analysis {
  public:

    LHCB_2010_I867355() : Analysis("LHCB_2010_I867355")
    {  }

    void init() {

      //@ Results are presented for two different fragmentation functions, LEP and Tevatron. Therefore, we have two sets of histograms.
      _h_sigma_vs_eta_lep = bookHisto1D(1, 1, 1);
      _h_sigma_vs_eta_tvt = bookHisto1D(1, 1, 2);
      _h_sigma_total_lep  = bookHisto1D(2, 1, 1);
      _h_sigma_total_tvt  = bookHisto1D(2, 1, 2);

    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      double weight = event.weight();

      Particles bhadrons;
      foreach (const GenParticle* p, particles(event.genEvent())) {
        if (!( PID::isHadron( p->pdg_id() ) && PID::hasBottom( p->pdg_id() )) ) continue;

        const GenVertex* dv = p->end_vertex();

        bool hasBdaughter = false;
        if ( PID::isHadron( p->pdg_id() ) && PID::hasBottom( p->pdg_id() )) { // selecting b-hadrons
          if (dv) {
            for (GenVertex::particles_out_const_iterator pp = dv->particles_out_const_begin() ; pp != dv->particles_out_const_end() ; ++pp) {
              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);
      }

      foreach (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*weight );
        _h_sigma_vs_eta_tvt->fill( eta, 0.5*weight );

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

  };


  // Hook for the plugin system
  DECLARE_RIVET_PLUGIN(LHCB_2010_I867355);

}