Rivet analyses

Hadronic Mass in τ− → 3π−2π+π0ντ

Experiment: CLEOII (CESR)

Inspire ID: 373188

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 73 (1994) 934-938

Beams: * *

Beam energies: ANY

Run details: - Tau production, can be any process but original data was in e+e− at the Υ(4S) resonance

Measurement of the invariant mass spectrum of the K−η system in τ → 3π−2π+π0ντ measured by CLEO at CESR.

Source code:CLEOII_1994_I373188.cc

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

namespace Rivet {


  /// @brief tau -> (5pi)-pi0
  class CLEOII_1994_I373188 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1994_I373188);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      declare(UnstableParticles(), "UFS");
      book(_hist, 1, 1, 1);
    }

    void findDecayProducts(const Particle& mother, unsigned int& nstable, Particles& pim, Particles& pi0) {
      for (const Particle& p : mother.children()) {
        long id = p.abspid();
        if (id == PID::PI0) {
          pi0.push_back(p);
          ++nstable;
        }
        else if (abs(id) == PID::PIPLUS) {
          pim.push_back(p);
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, pim, pi0);
        }
        else
          ++nstable;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::abspid == PID::TAU)) {
        Particles pi0, pim;
        unsigned int nstable = 0;
        // find the decay products we want
        findDecayProducts(p, nstable, pim, pi0);
        if (nstable != 7) continue;
        // K eta
        if (pim.size() == 5 && pi0.size() == 1) {
          FourMomentum phad = pi0[0].momentum();
          for (const Particle& p2 : pim) phad += p2.momentum();
          _hist->fill(phad.mass());
        }
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _hist;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CLEOII_1994_I373188);

}