Rivet analyses

title: ARGUS_1992_I335698

Hadronic mass spectrum and helicity angle in $\tau^-\to\pi^-\pi^0\nu_\tau$

Experiment: ARGUS (DORIS)

Inspire ID: 335698

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Z.Phys.C 56 (1992) 339-346

Beams: * *

Beam energies: ANY

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

Hadronic mass spectrum and helicity angle in $\tau^-\to\pi^-\pi^0\nu_\tau$. Corrected data read from figures 3 and 4 in the paper.

Source code:ARGUS_1992_I335698.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief tau -> pi- pi0 nu_tau class ARGUS_1992_I335698 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1992_I335698);


/// @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");
  // hists
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h[ix], 1 + ix, 1, 1);
  }
}


/// 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) {
    int sign = TAU.decaying()[ix].pid() > 0 ? 1 : -1;
    if (!(TAU.modeMatches(ix, 3, mode) || TAU.modeMatches(ix, 3, modeCC))) continue;
    const Particle& pi0 = TAU.decayProducts()[ix].at(111)[0];
    const Particle& pim = TAU.decayProducts()[ix].at(-211 * sign)[0];
    FourMomentum phad = pim.mom() + pi0.mom();
    _h[0]->fill(phad.mass());
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(phad.betaVec());
    FourMomentum ppi = boost.transform(pim.mom());
    const double cTheta = ppi.p3().unit().dot(phad.p3().unit());
    _h[1]->fill(cTheta);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
const map<PdgId, unsigned int> mode = {{111, 1}, {-211, 1}, {16, 1}};
const map<PdgId, unsigned int> modeCC = {{111, 1}, {211, 1}, {-16, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1992_I335698);

} ```