Rivet analyses

Spectral functions in τ− → π−π−π+π0ντ

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 τ− → π−π−π+π0ντ and τ− → π−ωντ, and the helicity angle in τ− → π−ωντ. The corrected data were read from figures 3 and 5 in the paper.

Source code:ARGUS_1987_I237930.cc

// -*- 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);

}