Rivet analyses

title: ARGUS_1987_I237930

Spectral functions in $\tau^-\to\pi^-\pi^-\pi^+\pi^0\nu_\tau$

Experiment: ARGUS (DORIS)

Inspire ID: 237930

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 185 (1987) 223

Beams: * *

Beam energies: ANY

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

Measurement of the spectral functions for $\tau^-\to\pi^-\pi^-\pi^+\pi^0\nu_\tau$ and $\tau^-\to\pi^-\omega\nu_\tau$, and the helicity angle in $\tau^-\to\pi^-\omega\nu_\tau$. The corrected data were read from figures 3 and 5 in the paper.

Source code:ARGUS_1987_I237930.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief tau -> pi- pi- pi+ pi0 class ARGUS_1987_I237930 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1987_I237930);


/// @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");
  // histograms
  book(_h_angle, 1, 1, 1);
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h_spect[ix], 2, 1, 1 + ix);
  }
  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();
    double q = phad.mass();
    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) continue;
    int ibatch = iomega == 0 ? 1 : 0;
    _h_spect[1]->fill(phad.mass(),
                      sqr(mtau) * mtau / q / sqr(sqr(mtau) - sqr(q)) / (sqr(mtau) + 2. * sqr(q)));
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(omega.mom().betaVec());
    Vector3 axis = boost.transform(pim[ibatch].mom());
    FourMomentum ppi0 = boost.transform(pi0.mom());
    FourMomentum ppip = boost.transform(pip.mom());
    Vector3 norm = ppi0.p3().cross(pip.p3()).unit();
    double cTheta = axis.dot(norm);
    _h_angle->fill(cTheta);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_angle, 1.0, false);
  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);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_spect[2], _h_angle;
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(ARGUS_1987_I237930);

} ```