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BABAR_2018_I1679886

Mass spectrum for $K^-K_S^0$ decays of the $\tau^-$ lepton
Experiment: BABAR (PEP-II)
Inspire ID: 1679886
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D98 (2018) no.3, 032010
Beams: * *
Beam energies: ANY
Run details:
  • e+ e- > tau+ tau-, or any process producing tau leptons

Mass spectra for $K^-K_S^0$ in tau decays measured by BaBar. Useful for testing models of the hadronic current in $\tau$ decays.

Source code: BABAR_2018_I1679886.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 BABAR_2018_I1679886 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2018_I1679886);
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_KK, 1, 1, 1);
24
25    }
26
27    void findDecayProducts(const Particle & mother, unsigned int & nstable,
28                           unsigned int & nK0, unsigned int & nKp,
29			   unsigned int & nKm, FourMomentum & ptot) {
30      for(const Particle & p : mother.children()) {
31        int id = p.pid();
32        if ( id == PID::KPLUS ) {
33	  ++nKp;
34          ++nstable;
35	  ptot += p.momentum();
36	}
37        else if (id == PID::KMINUS ) {
38	  ++nKm;
39          ++nstable;
40	  ptot += p.momentum();
41	}
42        else if (id == PID::K0S) {
43          ++nK0;
44          ++nstable;
45	  ptot += p.momentum();
46        }
47        else if (id == PID::PI0 || id == PID::PIPLUS || id == PID::PIMINUS) {
48          ++nstable;
49        }
50        else if ( !p.children().empty() ) {
51          findDecayProducts(p, nstable, nK0, nKp, nKm, ptot);
52        }
53        else
54          ++nstable;
55      }
56    }
57
58    /// Perform the per-event analysis
59    void analyze(const Event& event) {
60
61      // Loop over taus
62      for(const Particle& tau : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==PID::TAU)) {
63        unsigned int nstable(0),nK0(0),nKp(0),nKm(0);
64      	FourMomentum p_tot(0,0,0,0);
65        findDecayProducts(tau, nstable, nK0, nKp, nKm, p_tot);
66        if (tau.pid() < 0) {
67      	  swap(nKp,nKm);
68      	}
69       	if(nstable!=3) continue;
70      	if(nKm==1 && nK0==1 )
71          _h_KK->fill(p_tot.mass());
72      }
73
74
75    }
76
77
78    /// Normalise histograms etc., after the run
79    void finalize() {
80      normalize(_h_KK);
81    }
82
83    //@}
84
85
86    /// @name Histograms
87    //@{
88    Histo1DPtr _h_KK;
89    //@}
90
91
92  };
93
94
95  // The hook for the plugin system
96  RIVET_DECLARE_PLUGIN(BABAR_2018_I1679886);
97
98
99}