Rivet analyses

Measurement of σ(pp → bb̄X 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 b̄-flavoured hadrons is measured in different pseudorapidity intervals over the entire range of , assuming the LEP (and Tevatron) fractions for fragmentation into b-flavoured hadrons.

Source code:LHCB_2010_I867355.cc

// -*- 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);

}