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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
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4#include "Rivet/Projections/DecayedParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief tau -> pi- pi- pi+ pi0
 10  class ARGUS_1987_I237930 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1987_I237930);
 15
 16
 17    /// @name Analysis methods
 18    /// @{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      // Initialise and register projections
 23      UnstableParticles ufs = UnstableParticles(Cuts::abspid==15);
 24      declare(ufs, "UFS");
 25      DecayedParticles TAU(ufs);
 26      TAU.addStable(310);
 27      TAU.addStable(111);
 28      TAU.addStable(221);
 29      declare(TAU, "TAU");
 30      // histograms
 31      book(_h_angle,1,1,1);
 32      for (unsigned int ix=0; ix<2; ++ix) {
 33        book(_h_spect[ix], 2, 1, 1+ix);
 34      }
 35      book(_c,"TMP/nTau");
 36    }
 37
 38
 39    /// Perform the per-event analysis
 40    void analyze(const Event& event) {
 41      DecayedParticles TAU = apply<DecayedParticles>(event, "TAU");
 42      // loop over particles
 43      for (unsigned int ix=0;ix<TAU.decaying().size();++ix) {
 44        _c->fill();
 45      	int sign = TAU.decaying()[ix].pid()>0 ? 1 : -1;
 46      	if (!(TAU.modeMatches(ix,5,mode) || TAU.modeMatches(ix,5,modeCC)))  continue;
 47        const Particle & pi0 = TAU.decayProducts()[ix].at( 111     )[0];
 48        const Particles& pim = TAU.decayProducts()[ix].at(-211*sign);
 49        const Particle & pip = TAU.decayProducts()[ix].at( 211*sign)[0];
 50        FourMomentum phad = pim[0].mom()+pim[1].mom()+pip.mom()+pi0.mom();
 51        double q = phad.mass();
 52        double mtau = TAU.decaying()[ix].mass();
 53        _h_spect[0]->fill(phad.mass(),sqr(mtau)*mtau/q/sqr(sqr(mtau)-sqr(q))/(sqr(mtau)+2.*sqr(q)));
 54        Particle omega;
 55        int iomega=-1;
 56        for (unsigned int ix=0; ix<2; ++ix) {
 57          Particle parent = pim[ix];
 58          while (!parent.parents().empty()) {
 59            parent = parent.parents()[0];
 60            if (parent.pid()==223) break;
 61          }
 62          if (parent.pid()==223) {
 63            omega=parent;
 64            iomega=ix;
 65          }
 66        }
 67        if (iomega<0) continue;
 68        int ibatch = iomega == 0 ? 1 : 0;
 69        _h_spect[1]->fill(phad.mass(),sqr(mtau)*mtau/q/sqr(sqr(mtau)-sqr(q))/(sqr(mtau)+2.*sqr(q)));
 70        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(omega.mom().betaVec());
 71        Vector3 axis = boost.transform(pim[ibatch].mom());
 72        FourMomentum ppi0 = boost.transform(pi0.mom());
 73        FourMomentum ppip = boost.transform(pip.mom());
 74        Vector3 norm = ppi0.p3().cross(pip.p3()).unit();
 75        double cTheta = axis.dot(norm);
 76        _h_angle->fill(cTheta);
 77      }
 78    }
 79
 80
 81    /// Normalise histograms etc., after the run
 82    void finalize() {
 83      normalize(_h_angle, 1.0, false);
 84      const double Gamma = 6.582119514e-25/290.3e-15;
 85      const double GF    = 1.1663787e-5;
 86      const double cosC  = 0.97373;
 87      scale(_h_spect, Gamma*16.*sqr(M_PI)/sqr(GF*cosC)/ *_c);
 88    }
 89
 90    /// @}
 91
 92
 93    /// @name Histograms
 94    /// @{
 95    Histo1DPtr _h_spect[2],_h_angle;
 96    CounterPtr _c;
 97    const map<PdgId,unsigned int> mode   = { { 111,1},{-211,2},{ 211,1},{ 16,1}};
 98    const map<PdgId,unsigned int> modeCC = { { 111,1},{ 211,2},{-211,1},{-16,1}};
 99    /// @}
100
101
102  };
103
104
105  RIVET_DECLARE_PLUGIN(ARGUS_1987_I237930);
106
107}