Rivet analyses referenceBELLE_2006_I688850Helicity 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:
Beam energies: ANY Run details:
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}
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