Rivet analyses referenceARGUS_1992_I319105Decay asymmetries in Λ+c→Λ0π+Experiment: ARGUS (DORIS) Inspire ID: 319105 Status: VALIDATED Authors:
Beam energies: ANY Run details:
Measurement of the decay asymmetries in Λ+c→Λ0π+ by the ARGUS experiment. The asymmetry parameter is extracted by fitting to normalised angular distribution. N.B. the product of the asymmetry parameters for the Λc and daughter baryon is implemented as this is what is measured, rather than the extracted parameter for the Λc which relies on other measurements of the parameter for the daughter baryon. This analysis is useful for testing spin correlations in hadron decays. Source code: ARGUS_1992_I319105.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4
5namespace Rivet {
6
7
8 /// @brief Lambda_c -> Lambda pi asymmetry
9 class ARGUS_1992_I319105 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1992_I319105);
14
15
16 /// @name Analysis methods
17 /// @{
18
19 /// Book histograms and initialise projections before the run
20 void init() {
21 // Initialise and register projections
22 declare(UnstableParticles(), "UFS" );
23 // Book histograms
24 book(_h_ctheta,3,1,1);
25 }
26
27
28 /// Perform the per-event analysis
29 void analyze(const Event& event) {
30 // loop over Lambda_c baryons
31 for( const Particle& Lambdac : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==4122)) {
32 int sign = Lambdac.pid()/4122;
33 if(Lambdac.children().size()!=2) continue;
34 Particle baryon1,meson1;
35 if(Lambdac.children()[0].pid()==sign*3122 &&
36 Lambdac.children()[1].pid()==sign*211) {
37 baryon1 = Lambdac.children()[0];
38 meson1 = Lambdac.children()[1];
39 }
40 else if(Lambdac.children()[1].pid()==sign*3122 &&
41 Lambdac.children()[0].pid()==sign*211) {
42 baryon1 = Lambdac.children()[1];
43 meson1 = Lambdac.children()[0];
44 }
45 else
46 continue;
47 Particle baryon2,meson2;
48 if(baryon1.children()[0].pid()== sign*2212 &&
49 baryon1.children()[1].pid()==-sign*211) {
50 baryon2 = baryon1.children()[0];
51 meson2 = baryon1.children()[1];
52 }
53 else if(baryon1.children()[1].pid()== sign*2212 &&
54 baryon1.children()[0].pid()==-sign*211) {
55 baryon2 = baryon1.children()[1];
56 meson2 = baryon1.children()[0];
57 }
58 else
59 continue;
60 // first boost to the Lambdac rest frame
61 LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Lambdac.momentum().betaVec());
62 FourMomentum pbaryon1 = boost1.transform(baryon1.momentum());
63 FourMomentum pbaryon2 = boost1.transform(baryon2.momentum());
64 // to lambda rest frame
65 LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pbaryon1.betaVec());
66 Vector3 axis = pbaryon1.p3().unit();
67 FourMomentum pp = boost2.transform(pbaryon2);
68 // calculate angle
69 double cTheta = pp.p3().unit().dot(axis);
70 _h_ctheta->fill(cTheta);
71 }
72 }
73
74 pair<double,double> calcAlpha(Histo1DPtr hist) {
75 if(hist->numEntries()==0.) return make_pair(0.,0.);
76 double sum1(0.),sum2(0.);
77 for (const auto& bin : hist->bins() ) {
78 double Oi = bin.sumW();
79 if(Oi==0.) continue;
80 double ai = 0.5*(bin.xMax()-bin.xMin());
81 double bi = 0.5*ai*(bin.xMax()+bin.xMin());
82 double Ei = bin.errW();
83 sum1 += sqr(bi/Ei);
84 sum2 += bi/sqr(Ei)*(Oi-ai);
85 }
86 return make_pair(sum2/sum1,sqrt(1./sum1));
87 }
88
89
90 /// Normalise histograms etc., after the run
91 void finalize() {
92 normalize(_h_ctheta);
93 Estimate0DPtr _h_alpha;
94 book(_h_alpha,2,1,1);
95 pair<double,double> alpha = calcAlpha(_h_ctheta);
96 _h_alpha->set(alpha.first, alpha.second);
97 }
98
99 /// @}
100
101
102 /// @name Histograms
103 /// @{
104 Histo1DPtr _h_ctheta;
105 /// @}
106
107
108 };
109
110
111 RIVET_DECLARE_PLUGIN(ARGUS_1992_I319105);
112
113}
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