Rivet analyses referenceCLEOII_2005_I668268Decay asymmetry in $\Lambda^+_c\to\Lambda^0 e^+ \nu_e$Experiment: CLEOII (CESR) Inspire ID: 668268 Status: VALIDATED Authors:
Beam energies: ANY Run details:
Measurement of the decay asymmetry in $\Lambda^+_c\to\Lambda^0 e^+ \nu_e$ by CLEOII. The product of assymetries $\alpha_{\Lambda_c^+}\alpha_\Lambda$ is extracted as that is what is measured not $\alpha_{\Lambda_c^+}$ and there has been a significant change in $\alpha_\Lambda$ since this paper was published Source code: CLEOII_2005_I668268.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4
5namespace Rivet {
6
7
8 /// @brief Lambda_c -> Lambda e+ nu_e asymmetry
9 class CLEOII_2005_I668268 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_2005_I668268);
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
24 // Book histograms
25 book(_h_Lambda, "/TMP/hLambda", 20, -1.,1.);
26 }
27
28 void findChildren(Particle parent, int sign, unsigned int & npart,
29 Particles & lambda, Particles & e, Particles & nu) {
30 for(const Particle & child : parent.children()) {
31 if(child.pid()==sign*PID::LAMBDA) {
32 lambda.push_back(child);
33 ++npart;
34 }
35 else if(child.pid()==-sign*PID::EMINUS) {
36 e.push_back(child);
37 ++npart;
38 }
39 else if(child.pid()==sign*PID::NU_E) {
40 nu.push_back(child);
41 ++npart;
42 }
43 else if(!child.children().empty()) {
44 findChildren(child,sign,npart,lambda,e,nu);
45 }
46 else {
47 ++npart;
48 }
49 }
50 }
51
52 /// Perform the per-event analysis
53 void analyze(const Event& event) {
54 // loop over Lambda_c baryons
55 for( const Particle& Lambdac : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==4122)) {
56 int sign = Lambdac.pid()/4122;
57 Particles lambda,e,nu;
58 unsigned int npart(0);
59 findChildren(Lambdac,sign,npart,lambda,e,nu);
60 if(npart!=3 || lambda.size()!=1 || e.size()!=1 || nu.size()!=1) continue;
61 Particle baryon2;
62 if(lambda[0].children()[0].pid()== sign*2212 &&
63 lambda[0].children()[1].pid()== -sign*211) {
64 baryon2 = lambda[0].children()[0];
65 }
66 else if(lambda[0].children()[1].pid()== sign*2212 &&
67 lambda[0].children()[0].pid()== -sign*211) {
68 baryon2 = lambda[0].children()[1];
69 }
70 else
71 continue;
72 // first boost to the Lambdac rest frame
73 LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Lambdac.momentum().betaVec());
74 FourMomentum pbaryon1 = boost1.transform(lambda[0].momentum());
75 FourMomentum pbaryon2 = boost1.transform(baryon2 .momentum());
76 // to lambda rest frame
77 LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pbaryon1.betaVec());
78 Vector3 axis = pbaryon1.p3().unit();
79 FourMomentum pp = boost2.transform(pbaryon2);
80 // calculate angle
81 double cTheta = pp.p3().unit().dot(axis);
82 _h_Lambda->fill(cTheta);
83 }
84 }
85
86 pair<double,double> calcAlpha(Histo1DPtr hist) {
87 if(hist->numEntries()==0.) return make_pair(0.,0.);
88 double sum1(0.),sum2(0.);
89 for (const auto& bin : hist->bins() ) {
90 double Oi = bin.sumW();
91 if(Oi==0.) continue;
92 double ai = 0.5*(bin.xMax()-bin.xMin());
93 double bi = 0.5*ai*(bin.xMax()+bin.xMin());
94 double Ei = bin.errW();
95 sum1 += sqr(bi/Ei);
96 sum2 += bi/sqr(Ei)*(Oi-ai);
97 }
98 return make_pair(sum2/sum1,sqrt(1./sum1));
99 }
100
101 /// Normalise histograms etc., after the run
102 void finalize() {
103 // asymmetry
104 normalize(_h_Lambda);
105 Estimate1DPtr _h_alpha;
106 book(_h_alpha,1,1,1);
107 pair<double,double> alpha = calcAlpha(_h_Lambda);
108 _h_alpha->bin(1).set(alpha.first, alpha.second);
109 }
110 /// @}
111
112
113 /// @name Histograms
114 /// @{
115 Histo1DPtr _h_Lambda;
116 /// @}
117
118
119 };
120
121
122 RIVET_DECLARE_PLUGIN(CLEOII_2005_I668268);
123
124}
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