Rivet analyses

KS0π− spectrum in τ decays

Experiment: BELLE (KEKB)

Inspire ID: 753243

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B654 (2007) 65-73

Beams: * *

Beam energies: ANY

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

Measurement of the spectrum of KS0π− spectrum in τ decays by BELLE. Useful for testing models of the hadronic current in τ decays.

Source code:BELLE_2007_I753243.cc

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

namespace Rivet {


  /// @brief Add a short analysis description here
  class BELLE_2007_I753243 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2007_I753243);


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

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

      declare(UnstableParticles(), "UFS");
      book(_hist_Kpi, 1, 1, 1);
    }

    void findDecayProducts(const Particle& mother,
                           unsigned int& nstable,
                           unsigned int& npip,
                           unsigned int& npim,
                           unsigned int& nK,
                           FourMomentum& ptot) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::K0S) {
          ++nK;
          ++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::KPLUS || id == PID::KMINUS) {
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, npip, npim, nK, 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), nK(0);
        FourMomentum p_tot(0, 0, 0, 0);
        findDecayProducts(tau, nstable, npip, npim, nK, p_tot);
        if (tau.pid() < 0) swap(npip, npim);
        if (nstable == 3 && npim == 1 && nK == 1) _hist_Kpi->fill(p_tot.mass());
      }
    }


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

      normalize(_hist_Kpi);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _hist_Kpi;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2007_I753243);


}