Rivet analyses referenceBESIII_2018_I1627871Cross section for $e^+e^-\to\Lambda\bar{\Lambda}$ between threshold and 3.08 GeVExperiment: BESIII (BEPC II) Inspire ID: 1627871 Status: VALIDATED Authors:
Beam energies: ANY Run details:
Measurement of the cross section for $e^+e^-\to\Lambda\bar{\Lambda}$ between threshold and 3.08 GeV. Source code: BESIII_2018_I1627871.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_2018_I1627871 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1627871);
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, "/TMP/nLambda" );
26 }
27
28 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
29 for (const Particle &child : p.children()) {
30 if(child.children().empty()) {
31 nRes[child.pid()]-=1;
32 --ncount;
33 }
34 else
35 findChildren(child,nRes,ncount);
36 }
37 }
38
39 /// Perform the per-event analysis
40 void analyze(const Event& event) {
41 const FinalState& fs = apply<FinalState>(event, "FS");
42 // total hadronic and muonic cross sections
43 map<long,int> nCount;
44 int ntotal(0);
45 for (const Particle& p : fs.particles()) {
46 nCount[p.pid()] += 1;
47 ++ntotal;
48 }
49 // find the Lambdas
50 const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
51 for(unsigned int ix=0;ix<ufs.particles().size();++ix) {
52 const Particle& p1 = ufs.particles()[ix];
53 if(abs(p1.pid())!=3122) continue;
54 bool matched = false;
55 // check fs
56 bool fs = true;
57 for (const Particle & child : p1.children()) {
58 if(child.pid()==p1.pid()) {
59 fs = false;
60 break;
61 }
62 }
63 if(!fs) continue;
64 // find the children
65 map<long,int> nRes = nCount;
66 int ncount = ntotal;
67 findChildren(p1,nRes,ncount);
68 for(unsigned int iy=ix+1;iy<ufs.particles().size();++iy) {
69 const Particle& p2 = ufs.particles()[iy];
70 if(abs(p2.pid())!=3122) continue;
71 // check fs
72 bool fs = true;
73 for (const Particle & child : p2.children()) {
74 if(child.pid()==p2.pid()) {
75 fs = false;
76 break;
77 }
78 }
79 if(!fs) continue;
80 map<long,int> nRes2 = nRes;
81 int ncount2 = ncount;
82 findChildren(p2,nRes2,ncount2);
83 if(ncount2!=0) continue;
84 matched=true;
85 for(auto const & val : nRes2) {
86 if(val.second!=0) {
87 matched = false;
88 break;
89 }
90 }
91 if(matched) {
92 _nLambda->fill();
93 break;
94 }
95 }
96 if(matched) break;
97 }
98 }
99
100
101 /// Normalise histograms etc., after the run
102 void finalize() {
103 double sigma = _nLambda->val();
104 double error = _nLambda->err();
105 sigma *= crossSection()/ sumOfWeights() /picobarn;
106 error *= crossSection()/ sumOfWeights() /picobarn;
107 Estimate1D temphisto(refData(1, 1, 1));
108 Estimate1DPtr mult;
109 book(mult, 1, 1, 1);
110 for (auto& b : mult->bins()) {
111 if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
112 b.set(sigma, error);
113 }
114 }
115 }
116 /// @}
117
118 /// @name Histograms
119 /// @{
120 CounterPtr _nLambda;
121 /// @}
122 };
123
124
125 RIVET_DECLARE_PLUGIN(BESIII_2018_I1627871);
126
127
128}
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