Rivet analyses

title: CLEO_1999_I508944

Measurement of Semi-Leptonic Tau Decays into $\pi^\pm\pi^0$

Experiment: CLEO (CESR)

Inspire ID: 508944

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D61 (2000) 112002 - hep-ex/9910046

Beams: * *

Beam energies: ANY

Run details: - Tau production, can be any process but original data was in $e^+ e^-$ at the $\Upsilon(4S)$ resonance

Measurement of the invariant mass spectrum of the $\pi^-\pi^0$ system in $\tau\to\pi^-\pi^0\nu_\tau$ measured by CLEO at CESR.

Source code:CLEO_1999_I508944.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief tau -> pi-pi0 nu_tau class CLEO_1999_I508944 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_1999_I508944);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(UnstableParticles(), "UFS");
  book(_hist_pipi, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // Find the taus
  Particles taus;
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& p : ufs.particles()) {
    if (p.abspid() != PID::TAU) continue;
    Particles pip, pim, pi0;
    unsigned int nstable = 0;
    // get the boost to the rest frame
    // find the decay products we want
    findDecayProducts(p, nstable, pip, pim, pi0);
    if (p.pid() < 0) {
      swap(pip, pim);
    }
    if (nstable != 3) continue;
    // pipi
    if (pim.size() == 1 && pi0.size() == 1)
      _hist_pipi->fill((pi0[0].momentum() + pim[0].momentum()).mass());
  }
}

void findDecayProducts(const Particle& mother,
                       unsigned int& nstable,
                       Particles& pip,
                       Particles& pim,
                       Particles& pi0) {
  for (const Particle& p : mother.children()) {
    long id = p.pid();
    if (id == PID::PI0) {
      pi0.push_back(p);
      ++nstable;
    }
    else if (id == PID::PIPLUS) {
      pip.push_back(p);
      ++nstable;
    }
    else if (id == PID::PIMINUS) {
      pim.push_back(p);
      ++nstable;
    }
    else if (id == PID::K0S || id == PID::KPLUS || id == PID::KMINUS) {
      ++nstable;
    }
    else if (!p.children().empty()) {
      findDecayProducts(p, nstable, pip, pim, pi0);
    }
    else
      ++nstable;
  }
}

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

  normalize(_hist_pipi);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(CLEO_1999_I508944);

} ```