Rivet analyses

Bottom baryon polarization at LEP1

Experiment: DELPHI (LEP)

Inspire ID: 513614

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B474 (2000) 205-222

Beams: e- e+

Beam energies: (45.6, 45.6)GeV

Run details: - e+e- > hadrons

Measurement of the polarization of b-baryons, mainly Λ_b at LEP1. The result is obtained by measuring the ratio of the charged lepton energy to the neutrino (missing energy).

Source code:`DELPHI_2000_I513614.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief  b-baryon polarization
  class DELPHI_2000_I513614 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(DELPHI_2000_I513614);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_El, "El", 45, 0., 45.0);
      book(_h_Ev, "Ev", 45, 0., 45.0);
    }

    void findDecayProducts(Particle p, Particles& lep, Particles& nu) {
      for (const Particle& child : p.children()) {
        if (PID::isHadron(child.pid())) continue;
        if (child.abspid() == 11 or child.abspid() == 13)
          lep.push_back(child);
        else if (child.abspid() == 12 or child.abspid() == 14)
          nu.push_back(child);
        else if (child.abspid() != 15)
          findDecayProducts(child, lep, nu);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
      // loop over weakly decaying b-baryons
      for (const Particle& p : ufs.particles(Cuts::abspid == 5122 || Cuts::abspid == 5132
                                             || Cuts::abspid == 5232 || Cuts::abspid == 5332)) {
        Particles lep, nu;
        findDecayProducts(p, lep, nu);
        if (lep.size() != 1 || nu.size() != 1) continue;
        _h_El->fill(lep[0].momentum().t());
        _h_Ev->fill(nu[0].momentum().t());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_El);
      normalize(_h_Ev);
      if (_h_El->effNumEntries() != 0. and _h_Ev->effNumEntries() != 0.) {
        const double Ev = _h_Ev->xMean();
        const double El = _h_El->xMean();
        const double dEv = _h_Ev->xStdErr();
        const double dEl = _h_El->xStdErr();
        const double ratio = El / Ev;
        const double dr = (Ev * dEl - El * dEv) / sqr(Ev);
        const double rho = 0.091;
        const double P = (7. + rho * (30. - 40. * ratio) + 4. * (2. - 3. * ratio) * ratio)
            / sqr(1. + 2. * ratio);
        const double dP = (20. * (-1. + 4. * rho * (-2. + ratio) - 2. * ratio)) / pow(1. + 2. * ratio, 3)
            * dr;
        BinnedEstimatePtr<string> h_pol;
        book(h_pol, 1, 1, 1);
        h_pol->bin(1).set(P, dP);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_El, _h_Ev;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(DELPHI_2000_I513614);


}

Rivet analyses

Bottom baryon polarization at LEP1

Source code:DELPHI_2000_I513614.cc

Source code:`DELPHI_2000_I513614.cc`