Rivet analyses

title: ALEPH_1996_I421984

Tau decays to $\omega\pi^-$ and $\omega\pi^-\pi^0$

Experiment: ALEPH (LEP)

Inspire ID: 421984

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C74 (1997) 263-273

Beams: * *

Beam energies: ANY

Run details: - any process producing tau leptons

Measurement of mass spectra in the tau lepton decays $\tau^-\to\nu_\tau \pi^-\pi^+\pi^-\pi^0$ and $\tau^-\to\nu_\tau \pi^-\pi^0\pi^+\pi^-\pi^0$

Source code:ALEPH_1996_I421984.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief tau -> omega pi(pi) class ALEPH_1996_I421984 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_1996_I421984);


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

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

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

  // Book histograms
  book(_h_omegapi_momega[0], 1, 1, 1);
  book(_h_omegapi_momega[1], 2, 1, 1);
  book(_h_omegapi_momegapi, 3, 1, 1);
  book(_h_omegapipi_momega, 6, 1, 1);
}

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::K0S || id == PID::K0L)
      ++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::KPLUS) {
      ++nstable;
    }
    else if (id == PID::KMINUS) {
      ++nstable;
    }
    else if (!p.children().empty()) {
      findDecayProducts(p, nstable, pip, pim, pi0);
    }
    else
      ++nstable;
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // Find the taus
  Particles taus;
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == PID::TAU)) {
    Particles pip, pim, pi0;
    unsigned int nstable = 0;
    // Find the decay products we want
    findDecayProducts(p, nstable, pip, pim, pi0);
    if (p.pid() < 0) {
      swap(pip, pim);
    }
    if (nstable == 5 && pip.size() == 1 && pim.size() == 2 && pi0.size() == 1) {
      for (unsigned int ix = 0; ix < 2; ++ix) {
        double momega = (pim[ix].momentum() + pip[0].momentum() + pi0[0].momentum()).mass();
        _h_omegapi_momega[0]->fill(momega);
        _h_omegapi_momega[1]->fill(momega);
      }
      double mtotal = (pim[0].momentum() + pim[1].momentum() + pip[0].momentum() + pi0[0].momentum())
                          .mass();
      _h_omegapi_momegapi->fill(mtotal);
    }
    else if (nstable == 6 && pip.size() == 1 && pim.size() == 2 && pi0.size() == 2) {
      for (unsigned int ix = 0; ix < 2; ++ix) {
        for (unsigned int iy = 0; iy < 2; ++iy) {
          double momega = (pim[ix].momentum() + pip[0].momentum() + pi0[iy].momentum()).mass();
          _h_omegapipi_momega->fill(momega);
        }
      }
    }
  }
}


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

  // normalized measurement
  normalize(_h_omegapi_momegapi);
  // normalize to integral of data
  normalize(_h_omegapi_momega[0], 4164.8 * 0.01);
  normalize(_h_omegapi_momega[1], 5936.3 * 0.01);
  normalize(_h_omegapipi_momega, 1967.6 * 0.035);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_omegapi_momega[2], _h_omegapi_momegapi, _h_omegapipi_momega;
/// @}

};

RIVET_DECLARE_PLUGIN(ALEPH_1996_I421984);

} ```