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BELLE_2010_I841618

Mass spectra for $h^-h^-h^+$ decays of the $\tau^-$ lepton
Experiment: BELLE (KEKB)
Inspire ID: 841618
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D81 (2010) 113007
Beams: * *
Beam energies: ANY
Run details:
  • e+ e- > tau+ tau-, or any process producing tau leptons

Mass spectra for $\pi^+\pi^-\pi^+$, $K^-\pi^+\pi^-$, $K^+K^-\pi^-$ and $K^-K^-K^+$ in tau decays measured by BELLE. Useful for testing models of the hadronic current in $\tau$ decays.

Source code: BELLE_2010_I841618.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/UnstableParticles.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief Add a short analysis description here
  9  class BELLE_2010_I841618 : public Analysis {
 10  public:
 11
 12    /// Constructor
 13    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2010_I841618);
 14
 15
 16    /// @name Analysis methods
 17    //@{
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21
 22      declare(UnstableParticles(), "UFS");
 23      book(_h_3pi,   1, 1, 1);
 24      book(_h_Kpipi, 2, 1, 1);
 25      book(_h_KKpi,  3, 1, 1);
 26      book(_h_3K,    4, 1, 1);
 27
 28    }
 29
 30    void findDecayProducts(const Particle & mother, unsigned int & nstable,
 31                           unsigned int & npip, unsigned int & npim,
 32                           unsigned int & nKp, unsigned int & nKm, FourMomentum & ptot) {
 33      for(const Particle & p : mother.children()) {
 34        int id = p.pid();
 35        if ( id == PID::KPLUS ) {
 36	  ++nKp;
 37          ++nstable;
 38	  ptot += p.momentum();
 39	}
 40        else if (id == PID::KMINUS ) {
 41	  ++nKm;
 42          ++nstable;
 43	  ptot += p.momentum();
 44	}
 45        else if (id == PID::PIPLUS) {
 46          ++npip;
 47          ++nstable;
 48	  ptot += p.momentum();
 49        }
 50        else if (id == PID::PIMINUS) {
 51          ++npim;
 52          ++nstable;
 53	  ptot += p.momentum();
 54        }
 55        else if (id == PID::PI0 || id == PID::K0S) {
 56          ++nstable;
 57        }
 58        else if ( !p.children().empty() ) {
 59          findDecayProducts(p, nstable, npip, npim, nKp, nKm,ptot);
 60        }
 61        else
 62          ++nstable;
 63      }
 64    }
 65    
 66    /// Perform the per-event analysis
 67    void analyze(const Event& event) {
 68
 69      // Loop over taus
 70      for(const Particle& tau : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==PID::TAU)) {
 71        unsigned int nstable(0),npip(0),npim(0),nKp(0),nKm(0);
 72      	FourMomentum p_tot(0,0,0,0);
 73        findDecayProducts(tau, nstable, npip, npim, nKp, nKm, p_tot);
 74        if (tau.pid() < 0) {
 75      	  swap(npip, npim);
 76      	  swap(nKp,nKm);
 77      	}
 78       	if(nstable!=4) continue;
 79      	if(npim==2 && npip==1 )
 80          _h_3pi->fill(p_tot.mass());
 81      	else if(npim==1 && npip==1 && nKm==1)
 82          _h_Kpipi->fill(p_tot.mass());
 83      	else if(nKm==1 && nKp==1 && npim==1)
 84          _h_KKpi->fill(p_tot.mass());
 85      	else if(nKm==2 && nKp==1 )
 86          _h_3K->fill(p_tot.mass());
 87      }
 88    }
 89
 90
 91    /// Normalise histograms etc., after the run
 92    void finalize() {
 93
 94      normalize(_h_3pi); 
 95      normalize(_h_Kpipi); 
 96      normalize(_h_KKpi); 
 97      normalize(_h_3K); 
 98
 99    }
100
101    //@}
102
103
104    /// @name Histograms
105    //@{
106    Histo1DPtr _h_3pi, _h_Kpipi, _h_KKpi, _h_3K;
107    //@}
108
109
110  };
111
112
113  // The hook for the plugin system
114  RIVET_DECLARE_PLUGIN(BELLE_2010_I841618);
115
116
117}