Rivet analyses

Spectral functions in τ⁻ → π⁻π⁻π⁺π⁰ν_τ

Experiment: CLEOII (CESR)

Inspire ID: 505170

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 61 (2000) 072003

Beams: * *

Beam energies: ANY

Run details: - Any process producing tau leptons, originally e+e-

Measurement of the spectral functions for τ⁻ → π⁻π⁻π⁺π⁰ν_τ, τ⁻ → π⁻ων_τ and non-ω τ⁻ → π⁻π⁻π⁺π⁰ν_τ. The helicity angle in τ⁻ → π⁻ων_τ and mass distributions are also measured.

Source code:`CLEOII_2000_I505170.cc`

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

namespace Rivet {


  /// @brief  tau -> 4 pions
  class CLEOII_2000_I505170 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_2000_I505170);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 15);
      declare(ufs, "UFS");
      DecayedParticles TAU(ufs);
      TAU.addStable(310);
      TAU.addStable(111);
      TAU.addStable(221);
      declare(TAU, "TAU");
      // histos
      for (unsigned int ix = 0; ix < 6; ++ix) {
        book(_h_mass[ix], 3, 1, 1 + ix);
        if (ix > 2) continue;
        book(_h_spect[ix], 1, 1, 1 + ix);
      }
      book(_h_angle, 2, 1, 1);
      book(_c, "TMP/nTau");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      DecayedParticles TAU = apply<DecayedParticles>(event, "TAU");
      // loop over particles
      for (unsigned int ix = 0; ix < TAU.decaying().size(); ++ix) {
        _c->fill();
        int sign = TAU.decaying()[ix].pid() > 0 ? 1 : -1;
        if (!(TAU.modeMatches(ix, 5, mode) || TAU.modeMatches(ix, 5, modeCC))) continue;
        const Particle& pi0 = TAU.decayProducts()[ix].at(111)[0];
        const Particles& pim = TAU.decayProducts()[ix].at(-211 * sign);
        const Particle& pip = TAU.decayProducts()[ix].at(211 * sign)[0];
        FourMomentum phad = pim[0].mom() + pim[1].mom() + pip.mom() + pi0.mom();
        const double q = phad.mass();
        const double mtau = TAU.decaying()[ix].mass();
        _h_spect[0]->fill(phad.mass(),
                          sqr(mtau) * mtau / q / sqr(sqr(mtau) - sqr(q)) / (sqr(mtau) + 2. * sqr(q)));
        Particle omega;
        int iomega = -1;
        for (unsigned int ix = 0; ix < 2; ++ix) {
          Particle parent = pim[ix];
          while (!parent.parents().empty()) {
            parent = parent.parents()[0];
            if (parent.pid() == 223) break;
          }
          if (parent.pid() == 223) {
            omega = parent;
            iomega = ix;
          }
        }
        if (iomega >= 0) {
          _h_spect[1]->fill(phad.mass(),
                            sqr(mtau) * mtau / q / sqr(sqr(mtau) - sqr(q)) / (sqr(mtau) + 2. * sqr(q)));
          const int ibatch = iomega == 0 ? 1 : 0;
          const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(omega.mom().betaVec());
          const Vector3 axis = boost.transform(pim[ibatch].mom());
          const FourMomentum ppi0 = boost.transform(pi0.mom());
          const FourMomentum ppip = boost.transform(pip.mom());
          const Vector3 norm = ppi0.p3().cross(pip.p3()).unit();
          const double cTheta = axis.dot(norm);
          _h_angle->fill(cTheta);
        }
        else {
          _h_spect[2]->fill(phad.mass(),
                            sqr(mtau) * mtau / q / sqr(sqr(mtau) - sqr(q)) / (sqr(mtau) + 2. * sqr(q)));
        }
        _h_mass[0]->fill((phad - pim[0].mom()).mass());
        _h_mass[0]->fill((phad - pim[1].mom()).mass());
        _h_mass[1]->fill((pim[0].mom() + pi0.mom()).mass());
        _h_mass[1]->fill((pim[1].mom() + pi0.mom()).mass());
        _h_mass[2]->fill((pim[1].mom() + pip.mom()).mass());
        _h_mass[3]->fill((pip.mom() + pi0.mom()).mass());
        _h_mass[4]->fill(q);
        _h_mass[5]->fill((phad - pi0.mom()).mass());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double Gamma = 6.582119514e-25 / 290.3e-15;
      const double GF = 1.1663787e-5;
      const double cosC = 0.97373;
      scale(_h_spect, Gamma * 16. * sqr(M_PI) / sqr(GF * cosC) / *_c);
      normalize(_h_mass, 1.0, false);
      normalize(_h_angle, 1.0, false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_spect[3], _h_angle, _h_mass[6];
    CounterPtr _c;
    const map<PdgId, unsigned int> mode = {{111, 1}, {-211, 2}, {211, 1}, {16, 1}};
    const map<PdgId, unsigned int> modeCC = {{111, 1}, {211, 2}, {-211, 1}, {-16, 1}};
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CLEOII_2000_I505170);

}

Rivet analyses

Spectral functions in τ− → π−π−π+π0ντ

Source code:CLEOII_2000_I505170.cc

Spectral functions in τ⁻ → π⁻π⁻π⁺π⁰ν_τ

Source code:`CLEOII_2000_I505170.cc`