Rivet analyses

Mass spectra for h⁻h⁻h⁺ decays of the τ⁻ lepton

Experiment: BELLE (KEKB)

Inspire ID: 841618

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D81 (2010) 113007

Beams: * *

Beam energies: ANY

Run details: - e+ e- > tau+ tau-, or any process producing tau leptons

Mass spectra for π⁺π⁻π⁺, K⁻π⁺π⁻, K⁺K⁻π⁻ and K⁻K⁻K⁺ in tau decays measured by BELLE. Useful for testing models of the hadronic current in τ decays.

Source code:`BELLE_2010_I841618.cc`

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

namespace Rivet {


  /// @brief Add a short analysis description here
  class BELLE_2010_I841618 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2010_I841618);


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

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

      declare(UnstableParticles(), "UFS");
      book(_h_3pi, 1, 1, 1);
      book(_h_Kpipi, 2, 1, 1);
      book(_h_KKpi, 3, 1, 1);
      book(_h_3K, 4, 1, 1);
    }

    void findDecayProducts(const Particle& mother,
                           unsigned int& nstable,
                           unsigned int& npip,
                           unsigned int& npim,
                           unsigned int& nKp,
                           unsigned int& nKm,
                           FourMomentum& ptot) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::KPLUS) {
          ++nKp;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::KMINUS) {
          ++nKm;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::PIPLUS) {
          ++npip;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::PIMINUS) {
          ++npim;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::PI0 || id == PID::K0S) {
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, npip, npim, nKp, nKm, ptot);
        }
        else
          ++nstable;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {

      // Loop over taus
      for (const Particle& tau : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == PID::TAU)) {
        unsigned int nstable(0), npip(0), npim(0), nKp(0), nKm(0);
        FourMomentum p_tot(0, 0, 0, 0);
        findDecayProducts(tau, nstable, npip, npim, nKp, nKm, p_tot);
        if (tau.pid() < 0) {
          swap(npip, npim);
          swap(nKp, nKm);
        }
        if (nstable != 4) continue;
        if (npim == 2 && npip == 1)
          _h_3pi->fill(p_tot.mass());
        else if (npim == 1 && npip == 1 && nKm == 1)
          _h_Kpipi->fill(p_tot.mass());
        else if (nKm == 1 && nKp == 1 && npim == 1)
          _h_KKpi->fill(p_tot.mass());
        else if (nKm == 2 && nKp == 1)
          _h_3K->fill(p_tot.mass());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {

      normalize(_h_3pi);
      normalize(_h_Kpipi);
      normalize(_h_KKpi);
      normalize(_h_3K);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_3pi, _h_Kpipi, _h_KKpi, _h_3K;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2010_I841618);


}

Rivet analyses

Mass spectra for h−h−h+ decays of the τ− lepton

Source code:BELLE_2010_I841618.cc

Mass spectra for h⁻h⁻h⁺ decays of the τ⁻ lepton

Source code:`BELLE_2010_I841618.cc`