Rivet analyses

title: BELLE_2007_I753243

$K_S^0\pi^-$ spectrum in $\tau$ 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 $K_S^0\pi^-$ spectrum in $\tau$ decays by BELLE. Useful for testing models of the hadronic current in $\tau$ decays.

Source code:BELLE_2007_I753243.cc

```c++ // -- 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);

} ```