Rivet analyses referenceBESIII_2017_I1506414Analysis of $J/\psi$ and $\psi(2S)$ decays to $\Xi^0\bar\Xi^0$ and $\Sigma^{*0}\bar\Sigma^{*0}$Experiment: BESIII (BEPC) Inspire ID: 1506414 Status: VALIDATED Authors:
Beam energies: (1.6, 1.6); (1.8, 1.8) GeV Run details:
Analysis of the angular distribution of the baryons produced in $e^+e^-\to J/\psi,\psi(2S) \to \Xi^0\bar\Xi^0$ and $\Sigma^{*0}\bar\Sigma^{*0}$. Gives information about the decay and is useful for testing correlations in hadron decays. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2017_I1506414.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/Beam.hh"
4#include "Rivet/Projections/FinalState.hh"
5#include "Rivet/Projections/UnstableParticles.hh"
6
7namespace Rivet {
8
9
10 /// @brief Add a short analysis description here
11 class BESIII_2017_I1506414 : public Analysis {
12 public:
13
14 /// Constructor
15 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1506414);
16
17
18 /// @name Analysis methods
19 //@{
20
21 /// Book histograms and initialise projections before the run
22 void init() {
23
24 // Initialise and register projections
25 declare(Beam(), "Beams");
26 declare(UnstableParticles(), "UFS");
27 declare(FinalState(), "FS");
28
29 // Book histograms
30 if(isCompatibleWithSqrtS(3.1,1e-1)) {
31 book(_h_xi , 1, 1, 2);
32 book(_h_sig, 1, 1, 1);
33 }
34 else if (isCompatibleWithSqrtS(3.686, 1E-1)) {
35 book(_h_xi , 1, 1, 4);
36 book(_h_sig, 1, 1, 3);
37 }
38 }
39
40 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
41 for( const Particle &child : p.children()) {
42 if(child.children().empty()) {
43 nRes[child.pid()]-=1;
44 --ncount;
45 }
46 else
47 findChildren(child,nRes,ncount);
48 }
49 }
50
51 /// Perform the per-event analysis
52 void analyze(const Event& event) {
53 // get the axis, direction of incoming electron
54 const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
55 Vector3 axis;
56 if(beams.first.pid()>0)
57 axis = beams.first .momentum().p3().unit();
58 else
59 axis = beams.second.momentum().p3().unit();
60 // types of final state particles
61 const FinalState& fs = apply<FinalState>(event, "FS");
62 map<long,int> nCount;
63 int ntotal(0);
64 for (const Particle& p : fs.particles()) {
65 nCount[p.pid()] += 1;
66 ++ntotal;
67 }
68
69
70 const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
71 for (const Particle& p : ufs.particles(Cuts::abspid==3322 or Cuts::abspid==3214)) {
72 if(p.children().empty()) continue;
73 map<long,int> nRes=nCount;
74 int ncount = ntotal;
75 findChildren(p,nRes,ncount);
76 bool matched=false;
77 // check for antiparticle
78 for (const Particle& p2 : ufs.particles(Cuts::pid==-p.pid())) {
79 if(p2.children().empty()) continue;
80 map<long,int> nRes2=nRes;
81 int ncount2 = ncount;
82 findChildren(p2,nRes2,ncount2);
83 if(ncount2==0) {
84 matched = true;
85 for(auto const & val : nRes2) {
86 if(val.second!=0) {
87 matched = false;
88 break;
89 }
90 }
91 // fond baryon and antibaryon
92 if(matched) {
93 // calc cosine
94 double ctheta;
95 if(p.pid()>0)
96 ctheta = p .momentum().p3().unit().dot(axis);
97 else
98 ctheta = p2.momentum().p3().unit().dot(axis);
99 if(abs(p.pid())==3322)
100 _h_xi ->fill(ctheta);
101 else if(abs(p.pid())==3214)
102 _h_sig->fill(ctheta);
103 break;
104 }
105 }
106 }
107 if(matched) break;
108 }
109 }
110
111 pair<double,pair<double,double> > calcAlpha(Histo1DPtr hist) {
112 if(hist->numEntries()==0.) return make_pair(0.,make_pair(0.,0.));
113 double d = 3./(pow(hist->xMax(),3)-pow(hist->xMin(),3));
114 double c = 3.*(hist->xMax()-hist->xMin())/(pow(hist->xMax(),3)-pow(hist->xMin(),3));
115 double sum1(0.),sum2(0.),sum3(0.),sum4(0.),sum5(0.);
116 for (auto bin : hist->bins() ) {
117 double Oi = bin.area();
118 if(Oi==0.) continue;
119 double a = d*(bin.xMax() - bin.xMin());
120 double b = d/3.*(pow(bin.xMax(),3) - pow(bin.xMin(),3));
121 double Ei = bin.areaErr();
122 sum1 += a*Oi/sqr(Ei);
123 sum2 += b*Oi/sqr(Ei);
124 sum3 += sqr(a)/sqr(Ei);
125 sum4 += sqr(b)/sqr(Ei);
126 sum5 += a*b/sqr(Ei);
127 }
128 // calculate alpha
129 double alpha = (-c*sum1 + sqr(c)*sum2 + sum3 - c*sum5)/(sum1 - c*sum2 + c*sum4 - sum5);
130 // and error
131 double cc = -pow((sum3 + sqr(c)*sum4 - 2*c*sum5),3);
132 double bb = -2*sqr(sum3 + sqr(c)*sum4 - 2*c*sum5)*(sum1 - c*sum2 + c*sum4 - sum5);
133 double aa = sqr(sum1 - c*sum2 + c*sum4 - sum5)*(-sum3 - sqr(c)*sum4 + sqr(sum1 - c*sum2 + c*sum4 - sum5) + 2*c*sum5);
134 double dis = sqr(bb)-4.*aa*cc;
135 if(dis>0.) {
136 dis = sqrt(dis);
137 return make_pair(alpha,make_pair(0.5*(-bb+dis)/aa,-0.5*(-bb-dis)/aa));
138 }
139 else {
140 return make_pair(alpha,make_pair(0.,0.));
141 }
142 }
143
144 /// Normalise histograms etc., after the run
145 void finalize() {
146 // find energy
147 int ioff=-1;
148 if(isCompatibleWithSqrtS(3.1,1e-1)) ioff=0;
149 else if (isCompatibleWithSqrtS(3.686, 1E-1)) ioff=1;
150 normalize(_h_xi,1.,false);
151 Scatter2DPtr _h_alpha_xi;
152 book(_h_alpha_xi,2,2*ioff+2,1);
153 pair<double,pair<double,double> > alpha = calcAlpha(_h_xi);
154 _h_alpha_xi->addPoint(0.5, alpha.first, make_pair(0.5,0.5),
155 make_pair(alpha.second.first,alpha.second.second) );
156 normalize(_h_sig,1.,false);
157 Scatter2DPtr _h_alpha_sig;
158 book(_h_alpha_sig,2,2*ioff+1,1);
159 alpha = calcAlpha(_h_sig);
160 _h_alpha_sig->addPoint(0.5, alpha.first, make_pair(0.5,0.5),
161 make_pair(alpha.second.first,alpha.second.second) );
162
163 }
164 //@}
165
166 /// @name Histograms
167 //@{
168 Histo1DPtr _h_xi,_h_sig;
169 //@}
170
171
172 };
173
174
175 // The hook for the plugin system
176 RIVET_DECLARE_PLUGIN(BESIII_2017_I1506414);
177
178
179}
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