Rivet analyses

Pion helicity angle in τ− → π−π0ντ

Experiment: ARGUS (DORIS)

Inspire ID: 375417

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 337 (1994) 383-392

Beams: * *

Beam energies: ANY

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

Measurement of the pion helicity angle in the π−π0 frame for τ− → π−π0ντ. The corrected data were read from figure 3 in the paper.

Source code:ARGUS_1994_I375417.cc

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

namespace Rivet {


  /// @brief tau -> pi- pi0 nu_tau
  class ARGUS_1994_I375417 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1994_I375417);


    /// @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
      book(_b, {0.5, 0.69, 0.776, 0.85, 1.1});
      for (auto& b : _b->bins()) {
        book(b, 1, 1, b.index());
      }
    }


    /// 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();
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
            TAU.decaying()[ix].mom().betaVec());
        phad = boost.transform(phad);
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(phad.betaVec());
        FourMomentum ppi = boost2.transform(boost.transform(pim.mom()));
        const double cAlpha = ppi.p3().unit().dot(phad.p3().unit());
        _b->fill(phad.mass(), cAlpha);
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DGroupPtr _b;
    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_1994_I375417);

}