1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief eta' production in Upsilon(1S) decays
 9  class CLEOII_2002_I601701 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_2002_I601701);
14
15
16    /// @name Analysis methods
17    /// @{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21      declare(UnstableParticles(), "UFS");
22
23      book(_hist, 1, 1, 3);
24      book(_mult, 2, 1, 3);
25      book(_weightSum,"TMP/weightSum");
26
27    }
28
29    /// Recursively walk the decay tree to find decay products of @a p
30    void findDecayProducts(Particle mother, Particles& unstable) {
31      for(const Particle & p: mother.children()) {
32        const int id = abs(p.pid());
33	if ( id == 331 ) {
34	  unstable.push_back(p);
35	}
36	else if(!p.children().empty())
37	  findDecayProducts(p, unstable);
38      }
39    }
40
41    /// Perform the per-event analysis
42    void analyze(const Event& event) {
43      // find the Upsilon(1S) mesons
44      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
45      Particles upsilons = ufs.particles(Cuts::pid==553);
46      if(upsilons.empty()) vetoEvent;
47      // loop over them
48      for (const Particle& ups : upsilons) {
49	_weightSum->fill();
50	Particles unstable;
51	// Find the decay products we want
52	findDecayProducts(ups,unstable);
53	LorentzTransform cms_boost;
54	if (ups.p3().mod() > 0.001)
55	  cms_boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
56	double mass = ups.mass();
57	_mult->fill(unstable.size());
58	// fill the spectrum
59	for( const Particle & p : unstable) {
60	  FourMomentum p2 = cms_boost.transform(p.momentum());
61	  double xp = 2.*p2.E()/mass;
62	  _hist->fill(xp);
63	}
64      }
65    }
66
67
68    /// Normalise histograms etc., after the run
69    void finalize() {
70      // spectrum
71      if (_weightSum->val() > 0.)
72        scale(_hist, 1. / *_weightSum);
73      // BR
74      scale(_mult,1./ *_weightSum);
75    }
76
77    /// @}
78
79
80    /// @name Histograms
81    /// @{
82    Histo1DPtr _hist;
83    CounterPtr _mult;
84    CounterPtr _weightSum;
85    /// @}
86
87
88  };
89
90
91  RIVET_DECLARE_PLUGIN(CLEOII_2002_I601701);
92
93}