Rivet analyses

title: ALEPH_2001_I558327

Study of the fragmentation of b quarks into B mesons at the Z peak

Experiment: ALEPH (LEP 1)

Inspire ID: 558327

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett.B512:30-48,2001. - hep-ex/0106051

Beams: e+ e-

Beam energies: (45.6, 45.6)GeV

Run details: - Hadronic Z decay events generated on the Z pole ($\sqrt{s} = 91.2$ GeV)

Measurement of the $b$-quark fragmentation function by ALEPH using LEP 1 data. The fragmentation function for both weakly decaying and leading $b$-quarks has been determined. The data used for the plots has been renormalised to give a differential distribution rather than the bin-by-bin average in HEPDATA.

Source code:ALEPH_2001_I558327.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief DELPHI b-fragmentation measurement /// /// @author Hendrik Hoeth class ALEPH_2001_I558327 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_2001_I558327);


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

/// Book projections and histograms
void init() {
  declare(Beam(), "Beams");
  declare(ChargedFinalState(), "FS");
  book(_histXbweak, 1, 1, 1);
  book(_histXbprim, 1, 1, 2);
  book(_histMeanXbweak, 7, 1, 1);
  book(_histMeanXbprim, 7, 1, 2);
}


/// Analyse each event
void analyze(const Event& e) {
  const FinalState& fs = apply<FinalState>(e, "FS");
  const size_t numParticles = fs.particles().size();

  // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
  if (numParticles < 2) {
    MSG_DEBUG("Failed ncharged cut");
    vetoEvent;
  }
  MSG_DEBUG("Passed ncharged cut");

  // Get beams and average beam momentum
  const ParticlePair& beams = apply<Beam>(e, "Beams").beams();
  const double meanBeamMom = (beams.first.p3().mod() + beams.second.p3().mod()) / 2.0;
  MSG_DEBUG("Avg beam momentum = " << meanBeamMom);


  for (ConstGenParticlePtr p : HepMCUtils::particles(e.genEvent())) {
    ConstGenVertexPtr pv = p->production_vertex();
    ConstGenVertexPtr dv = p->end_vertex();
    if (PID::isBottomHadron(p->pdg_id())) {
      const double xp = p->momentum().e() / meanBeamMom;

      // If the B-hadron has a parton as parent, call it primary B-hadron:
      if (pv) {
        bool is_primary = false;
        for (ConstGenParticlePtr pp : HepMCUtils::particles(pv, Relatives::PARENTS)) {
          if (isParton(pp->pdg_id())) is_primary = true;
        }
        if (is_primary) {
          _histXbprim->fill(xp);
          _histMeanXbprim->fill(_histMeanXbprim->bin(1).xMid(), xp);
        }
      }

      // If the B-hadron has no B-hadron as a child, it decayed weakly:
      if (dv) {
        bool is_weak = true;
        for (ConstGenParticlePtr pp : HepMCUtils::particles(dv, Relatives::CHILDREN)) {
          if (PID::isBottomHadron(pp->pdg_id())) {
            is_weak = false;
          }
        }
        if (is_weak) {
          _histXbweak->fill(xp);
          _histMeanXbweak->fill(_histMeanXbweak->bin(1).xMid(), xp);
        }
      }
    }
  }
}


/// Finalize the histograms
void finalize() {
  normalize(_histXbprim);
  normalize(_histXbweak);
}

/// @}


/// @name Helper functions
/// @note The PID:: namespace functions would be preferable, but don't have exactly the same behaviour. Preserving the original form.
/// @{
bool isParton(int id) {
  return abs(id) <= 100 && abs(id) != 22 && (abs(id) < 11 || abs(id) > 18);
}
// bool isBHadron(int id) { return ((abs(id)/100)%10 == 5) || (abs(id) >= 5000 && abs(id) <= 5999); }
/// @}


/// @name Histograms
///
/// Store the weighted sums of numbers of charged / charged+neutral
/// particles - used to calculate average number of particles for the
/// inclusive single particle distributions' normalisations.
/// @{
Histo1DPtr _histXbprim;
Histo1DPtr _histXbweak;
Profile1DPtr _histMeanXbprim;
Profile1DPtr _histMeanXbweak;
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(ALEPH_2001_I558327, ALEPH_2001_S4656318);

} ```

Aliases: - ALEPH_2001_S4656318