1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief B -> Ds1(2460) Dbar
 9  class BABAR_2004_I656424 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2004_I656424);
14
15
16    /// @name Analysis methods
17    /// @{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21      // Initialise and register projections
22      UnstableParticles ufs = UnstableParticles(Cuts::abspid==511||
23						Cuts::abspid==521);
24      declare(ufs, "UFS");
25      // histos
26      book(_h,1,1,1);
27    }
28
29
30    /// Perform the per-event analysis
31    void analyze(const Event& event) {
32      Particles BB = apply<UnstableParticles>(event, "UFS").particles();
33      for(const Particle & p : BB) {
34	if(p.children().size()!=2) continue;
35	int sign = p.pid()/p.abspid();
36	int iD = -sign*(p.abspid()-100);
37	Particle Ds1;
38	if(p.children()[0].pid()==sign*20433 &&
39	   p.children()[1].pid()==iD) {
40	  Ds1=p.children()[0];
41	}
42	else if(p.children()[1].pid()==sign*20433 &&
43		p.children()[0].pid()==iD) {
44	  Ds1=p.children()[1];
45	}
46	else
47	  continue;
48	// find children of the Ds1 meson
49	Particle Ds;
50	if(Ds1.children().size()!=2) continue;
51	if(Ds1.children()[0].abspid()==431 &&
52	   Ds1.children()[1].abspid()==22)
53	  Ds = Ds1.children()[0];
54	else if (Ds1.children()[1].abspid()==431 &&
55		 Ds1.children()[0].abspid()==22)
56	  Ds = Ds1.children()[1];
57	else
58	  continue;
59	// boost to rest frame
60	LorentzTransform boostB  = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
61	FourMomentum pDs1  = boostB.transform(Ds1.momentum());
62	FourMomentum pDs   = boostB.transform(Ds .momentum());
63	LorentzTransform boostDs1 = LorentzTransform::mkFrameTransformFromBeta(pDs1.betaVec());
64	pDs = boostDs1.transform(pDs);
65	Vector3 axis = pDs1.p3().unit();
66	double cTheta = axis.dot(pDs.p3().unit());
67	_h->fill(cTheta);
68      }
69    }
70
71
72    /// Normalise histograms etc., after the run
73    void finalize() {
74      normalize(_h,1.,false);
75    }
76
77    /// @}
78
79
80    /// @name Histograms
81    /// @{
82    Histo1DPtr _h;
83    /// @}
84
85
86  };
87
88
89  RIVET_DECLARE_PLUGIN(BABAR_2004_I656424);
90
91}