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BELLE_2006_I688850

Helicity angle and mass distribution for $\pi^+\pi^-$ in $B^0\to\rho^0\pi^0$
Experiment: BELLE (KEKB)
Inspire ID: 688850
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 73 (2006) 111105
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing B0 mesons, originally Upsilon(4S) decays

Measurement of the helicity angle and mass distribution for $\pi^+\pi^-$ in $B^0\to\rho^0\pi^0$

Source code: BELLE_2006_I688850.cc
 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 B0 -> rho0 pi0
10  class BELLE_2006_I688850 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2006_I688850);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      // projections
23      UnstableParticles ufs = UnstableParticles(Cuts::abspid==511);
24      declare(ufs, "UFS");
25      DecayedParticles B0(ufs);
26      B0.addStable( 111);
27      declare(B0, "B0");
28      // histos
29      for(unsigned int ix=0;ix<2;++ix) {
30        book(_h[ix],1,1,1+ix);
31      }
32    }
33
34
35    /// Perform the per-event analysis
36    void analyze(const Event& event) {
37      DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
38      for(unsigned int ix=0; ix<B0.decaying().size(); ++ix) {
39      	int sign = B0.decaying()[ix].pid()/B0.decaying()[ix].abspid();
40      	if (!B0.modeMatches(ix,3,mode)) continue;
41       	const Particle& pip = B0.decayProducts()[ix].at( sign*211)[0];
42       	const Particle& pim = B0.decayProducts()[ix].at(-sign*211)[0];
43       	const Particle& pi0 = B0.decayProducts()[ix].at(      111)[0];
44        // require pi+- pi0 mass >1.1 GeV
45        if((pip.mom()+pi0.mom()).mass()<1.1) continue;
46        if((pim.mom()+pi0.mom()).mass()<1.1) continue;
47        FourMomentum pRho = pip.mom()+pim.mom();
48        _h[0]->fill(pRho.mass());
49       	// compute the helicity angle
50        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(B0.decaying()[ix].mom().betaVec());
51      	pRho = boost1.transform(pRho);
52      	FourMomentum ppi  = boost1.transform(pip.mom());
53        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pRho.betaVec());
54        ppi = boost2.transform(ppi);
55        const double cTheta = ppi.p3().unit().dot(pRho.p3().unit());
56        _h[1]->fill(cTheta);
57      }
58    }
59
60
61    /// Normalise histograms etc., after the run
62    void finalize() {
63      normalize(_h, 1.0, false);
64    }
65
66    /// @}
67
68
69    /// @name Histograms
70    /// @{
71    Histo1DPtr _h[2];
72    const map<PdgId,unsigned int> mode = { { 211,1}, {-211,1}, { 111,1} };
73    /// @}
74
75
76  };
77
78
79  RIVET_DECLARE_PLUGIN(BELLE_2006_I688850);
80
81}