1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4#include "Rivet/Projections/DecayedParticles.hh"
 5
 6namespace Rivet {
 7
 8
 9  /// @brief B -> D rho
10  class BELLE_2024_I2778312 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2024_I2778312);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      UnstableParticles ufs = UnstableParticles(Cuts::pid==-521);
23      declare(ufs, "UFS");
24      DecayedParticles BP(ufs);
25      BP.addStable(421);
26      BP.addStable(111);
27      declare(BP, "BP");
28      for(unsigned int ix=0;ix<2;++ix)
29        book(_h[ix],1,1,1+ix);
30    }
31
32
33    /// Perform the per-event analysis
34    void analyze(const Event& event) {
35      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
36      for (unsigned int ix=0; ix<BP.decaying().size(); ++ix) {
37      	if ( ! BP.modeMatches(ix,3,mode)) continue;
38        const Particle& pim = BP.decayProducts()[ix].at(-211)[0];
39        const Particle& pi0 = BP.decayProducts()[ix].at( 111)[0];
40        // compute the helicity angles
41        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(BP.decaying()[ix].mom().betaVec());
42
43        // pi pi mass and angle
44        FourMomentum ppipi = pim.mom()+pi0.mom();
45        ppipi = boost1.transform(ppipi);
46        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(ppipi.betaVec());
47        FourMomentum pPi  = boost1.transform(pim.mom());
48        FourMomentum pPi3 = boost2.transform(pPi);
49        double cTheta = -pPi3.p3().unit().dot(ppipi.p3().unit());
50        if(cTheta>0.7) continue;
51        _h[0]->fill(cTheta);
52        _h[1]->fill(ppipi.mass()/GeV);
53      }
54    }
55
56
57    /// Normalise histograms etc., after the run
58    void finalize() {
59      for(unsigned int ix=0;ix<2;++ix)
60        normalize(_h[ix],1.,false);
61    }
62
63    /// @}
64
65
66    /// @name Histograms
67    /// @{
68    Histo1DPtr _h[2];
69    const map<PdgId,unsigned int> mode= { {-211,1}, {111,1}, {421,1}};
70    /// @}
71
72
73  };
74
75
76  RIVET_DECLARE_PLUGIN(BELLE_2024_I2778312);
77
78}