Rivet analyses referenceBESIII_2021_I1900124Cross section for $e^+e^-\to\Lambda\bar{\Lambda}$ between 3.5 and 4.6 GeVExperiment: BESIII (BEPC) Inspire ID: 1900124 Status: VALIDATED Authors:
Beam energies: (1.8, 1.8); (1.8, 1.8); (1.8, 1.8); (1.8, 1.8); (1.8, 1.8); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (2.0, 2.0); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.3, 2.3) GeV Run details:
Measurement of the cross section for $e^+e^-\to\Lambda\bar{\Lambda}$ between 3.5 and 4.6 GeV. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2021_I1900124.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/FinalState.hh"
4#include "Rivet/Projections/UnstableParticles.hh"
5
6namespace Rivet {
7
8
9 /// @brief Lambda Lambdabar cross section
10 class BESIII_2021_I1900124 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1900124);
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 declare(FinalState(), "FS");
24 declare(UnstableParticles(), "UFS");
25 book(_nLambda, 1, 1, 1);
26 for (const string& en : _nLambda.binning().edges<0>()) {
27 const double end = std::stod(en)*GeV;
28 if (isCompatibleWithSqrtS(end)) {
29 _ecms = en;
30 break;
31 }
32 }
33 if(_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
34 }
35
36 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
37 for (const Particle &child : p.children()) {
38 if(child.children().empty()) {
39 nRes[child.pid()]-=1;
40 --ncount;
41 }
42 else
43 findChildren(child,nRes,ncount);
44 }
45 }
46
47
48 /// Perform the per-event analysis
49 void analyze(const Event& event) {
50 const FinalState& fs = apply<FinalState>(event, "FS");
51 // total hadronic and muonic cross sections
52 map<long,int> nCount;
53 int ntotal(0);
54 for (const Particle& p : fs.particles()) {
55 nCount[p.pid()] += 1;
56 ++ntotal;
57 }
58 // find the Lambdas
59 const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
60 for(unsigned int ix=0;ix<ufs.particles().size();++ix) {
61 const Particle& p1 = ufs.particles()[ix];
62 if(abs(p1.pid())!=3122) continue;
63 bool matched = false;
64 // check fs
65 bool fs = true;
66 for (const Particle & child : p1.children()) {
67 if(child.pid()==p1.pid()) {
68 fs = false;
69 break;
70 }
71 }
72 if(!fs) continue;
73 // find the children
74 map<long,int> nRes = nCount;
75 int ncount = ntotal;
76 findChildren(p1,nRes,ncount);
77 for(unsigned int iy=ix+1;iy<ufs.particles().size();++iy) {
78 const Particle& p2 = ufs.particles()[iy];
79 if(abs(p2.pid())!=3122) continue;
80 // check fs
81 bool fs = true;
82 for (const Particle & child : p2.children()) {
83 if(child.pid()==p2.pid()) {
84 fs = false;
85 break;
86 }
87 }
88 if(!fs) continue;
89 map<long,int> nRes2 = nRes;
90 int ncount2 = ncount;
91 findChildren(p2,nRes2,ncount2);
92 if(ncount2!=0) continue;
93 matched=true;
94 for(auto const & val : nRes2) {
95 if(val.second!=0) {
96 matched = false;
97 break;
98 }
99 }
100 if(matched) {
101 _nLambda->fill(_ecms);
102 break;
103 }
104 }
105 if(matched) break;
106 }
107 }
108
109
110 /// Normalise histograms etc., after the run
111 void finalize() {
112 scale(_nLambda, crossSection()/ sumOfWeights() /femtobarn);
113 }
114
115 ///@}
116
117
118 /// @name Histograms
119 ///@{
120 BinnedHistoPtr<string> _nLambda;
121 string _ecms;
122 ///@}
123
124
125 };
126
127
128 RIVET_DECLARE_PLUGIN(BESIII_2021_I1900124);
129
130}
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