Rivet analyses referenceBABAR_2009_I819092Mass distributions and ˉΛ0 polarization in B0→ˉΛ0pπ−Experiment: BABAR (PEP-II) Inspire ID: 819092 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
Measurement of the ˉΛ0p mass spectrum and ˉΛ0 energy in the decay B0→ˉΛ0pπ−. The polarization of the ˉΛ0 is also measured. The data were read from the plots/tables in the paper but are efficiency corrected and background subtracted. In additon the values of the polarization were adjusted to use the PDG 2022 value of αΛ as there has been a significant change due to due measuremnts. Source code: BABAR_2009_I819092.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 -> lambdabar p pi-
10 class BABAR_2009_I819092 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I819092);
15
16
17 /// @name Analysis methods
18 /// @{
19
20 /// Book histograms and initialise projections before the run
21 void init() {
22 // Initialise and register projections
23 UnstableParticles ufs = UnstableParticles(Cuts::pid==511);
24 declare(ufs, "UFS");
25 DecayedParticles B0(ufs);
26 B0.addStable( 3122);
27 B0.addStable(-3122);
28 declare(B0, "B0");
29 book(_h_pol1,2,1,1);
30 for(unsigned int ix=0;ix<3;++ix) {
31 if(ix<2) book(_h_mass[ix],1,1,1+ix);
32 book(_h_pol2[ix],3,1,1+ix);
33 }
34 }
35
36
37 /// Perform the per-event analysis
38 void analyze(const Event& event) {
39 double alpha = -0.732;
40 static const map<PdgId,unsigned int> & mode = { { 2212,1},{-3122,1}, {-211,1}};
41 DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
42 // loop over particles
43 for(unsigned int ix=0;ix<B0.decaying().size();++ix) {
44 if (!B0.modeMatches(ix,3,mode)) continue;
45 const Particle & pp = B0.decayProducts()[ix].at( 2212)[0];
46 const Particle & LamBar = B0.decayProducts()[ix].at(-3122)[0];
47 _h_mass[0]->fill( (pp.momentum()+LamBar.momentum()).mass());
48 // boost to B rest frame
49 LorentzTransform boost =
50 LorentzTransform::mkFrameTransformFromBeta(B0.decaying()[ix]. momentum().betaVec());
51 FourMomentum pLam = boost.transform(LamBar.momentum());
52 FourMomentum pProton = boost.transform(pp .momentum());
53 _h_mass[1]->fill(pLam.E());
54 // Lambda decay products
55 if(LamBar.children().size()!=2) continue;
56 Particle pbar;
57 if(LamBar.children()[0].pid()==-2212 &&
58 LamBar.children()[1].pid()== 211) {
59 pbar = LamBar.children()[0];
60 }
61 else if(LamBar.children()[1].pid()==-2212 &&
62 LamBar.children()[0].pid()== 211) {
63 pbar = LamBar.children()[1];
64 }
65 else
66 continue;
67 LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pLam.betaVec());
68 Vector3 axisP = boost2.transform(boost.transform(pbar.momentum())).p3().unit();
69 Vector3 axis1 = pLam.p3().unit();
70 double cTheta = axisP.dot(axis1);
71 _h_pol1 ->fill(pLam.E(),3.*cTheta);
72 _h_pol2[0]->fill(pLam.E(),3.*cTheta/alpha);
73 Vector3 axis2 = pLam.p3().cross(pProton.p3()).unit();
74 cTheta = axisP.dot(axis2);
75 _h_pol2[1]->fill(pLam.E(),3.*cTheta/alpha);
76 Vector3 axis3 = axis1.cross(axis2);
77 cTheta = axisP.dot(axis3);
78 _h_pol2[2]->fill(pLam.E(),3.*cTheta/alpha);
79 }
80 }
81
82
83 /// Normalise histograms etc., after the run
84 void finalize() {
85 for(unsigned int ix=0;ix<2;++ix)
86 normalize(_h_mass[ix],1.,false);
87 }
88
89 /// @}
90
91
92 /// @name Histograms
93 /// @{
94 Histo1DPtr _h_mass[2];
95 Profile1DPtr _h_pol1,_h_pol2[3];
96 /// @}
97
98
99 };
100
101
102 RIVET_DECLARE_PLUGIN(BABAR_2009_I819092);
103
104}
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