Rivet analyses referenceBABAR_2009_I819092Mass distributions and $\bar{\Lambda}^0$ polarization in $B^0\to \bar{\Lambda}^0 p\pi^-$Experiment: BABAR (PEP-II) Inspire ID: 819092 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
Measurement of the $\bar\Lambda^0 p$ mass spectrum and $\bar\Lambda^0$ energy in the decay $B^0\to\bar{\Lambda}^0 p \pi^-$. The polarization of the $\bar\Lambda^0$ 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 $\alpha_\Lambda$ 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 static const map<PdgId,unsigned int> & mode = { { 2212,1},{-3122,1}, {-211,1}};
40 DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
41 // loop over particles
42 for(unsigned int ix=0;ix<B0.decaying().size();++ix) {
43 if (!B0.modeMatches(ix,3,mode)) continue;
44 const Particle & pp = B0.decayProducts()[ix].at( 2212)[0];
45 const Particle & LamBar = B0.decayProducts()[ix].at(-3122)[0];
46 _h_mass[0]->fill( (pp.momentum()+LamBar.momentum()).mass());
47 // boost to B rest frame
48 LorentzTransform boost =
49 LorentzTransform::mkFrameTransformFromBeta(B0.decaying()[ix]. momentum().betaVec());
50 FourMomentum pLam = boost.transform(LamBar.momentum());
51 FourMomentum pProton = boost.transform(pp .momentum());
52 _h_mass[1]->fill(pLam.E());
53 // Lambda decay products
54 if(LamBar.children().size()!=2) continue;
55 Particle pbar;
56 if(LamBar.children()[0].pid()==-2212 &&
57 LamBar.children()[1].pid()== 211) {
58 pbar = LamBar.children()[0];
59 }
60 else if(LamBar.children()[1].pid()==-2212 &&
61 LamBar.children()[0].pid()== 211) {
62 pbar = LamBar.children()[1];
63 }
64 else
65 continue;
66 LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pLam.betaVec());
67 Vector3 axisP = boost2.transform(boost.transform(pbar.momentum())).p3().unit();
68 Vector3 axis1 = pLam.p3().unit();
69 double cTheta = axisP.dot(axis1);
70 _h_pol1 ->fill(pLam.E(),3.*cTheta);
71 _h_pol2[0]->fill(pLam.E(),3.*cTheta);
72 Vector3 axis2 = pLam.p3().cross(pProton.p3()).unit();
73 cTheta = axisP.dot(axis2);
74 _h_pol2[1]->fill(pLam.E(),3.*cTheta);
75 Vector3 axis3 = axis1.cross(axis2);
76 cTheta = axisP.dot(axis3);
77 _h_pol2[2]->fill(pLam.E(),3.*cTheta);
78 }
79 }
80
81
82 /// Normalise histograms etc., after the run
83 void finalize() {
84 double alpha = -0.732;
85 for(unsigned int ix=0;ix<2;++ix) {
86 if(ix<2) normalize(_h_mass[ix],1.,false);
87 _h_pol2[ix]->scale(2, 1./alpha);
88 }
89 }
90
91 /// @}
92
93
94 /// @name Histograms
95 /// @{
96 Histo1DPtr _h_mass[2];
97 Profile1DPtr _h_pol1,_h_pol2[3];
98 /// @}
99
100
101 };
102
103
104 RIVET_DECLARE_PLUGIN(BABAR_2009_I819092);
105
106}
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