Rivet analyses referenceBESIII_2022_I2182758Cross section for $e^+e^-\to J/\psi K^0_SK^0_S$ at energies between 4.126 and 4.95 GeVExperiment: BESIII (BEPC) Inspire ID: 2182758 Status: VALIDATED NOHEPDATA Authors:
Beam energies: (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); (2.2, 2.2); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.4, 2.4); (2.4, 2.4); (2.4, 2.4); (2.4, 2.4); (2.5, 2.5); (2.5, 2.5) GeV Run details:
Measurement of the cross section for $e^+e^-\to J/\psi K^0_SK^0_S$ at energies between 4.126 and 4.95 GeV. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2022_I2182758.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 e+e- > KS0 KS0 J/psi
10 class BESIII_2022_I2182758 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2182758);
15
16
17 /// @name Analysis methods
18 /// @{
19
20 /// Book histograms and initialise projections before the run
21 void init() {
22 declare(FinalState(), "FS");
23 declare(UnstableParticles(), "UFS");
24 book(_sigmaPsi, 1,1,1);
25 for (const string& en : _sigmaPsi.binning().edges<0>()) {
26 double end = std::stod(en)*GeV;
27 if(isCompatibleWithSqrtS(end)) {
28 _ecms = en;
29 break;
30 }
31 }
32 if(_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
33 }
34
35 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
36 for (const Particle& child : p.children()) {
37 if (child.children().empty()) {
38 --nRes[child.pid()];
39 --ncount;
40 }
41 else {
42 findChildren(child,nRes,ncount);
43 }
44 }
45 }
46
47 /// Perform the per-event analysis
48 void analyze(const Event& event) {
49 const FinalState& fs = apply<FinalState>(event, "FS");
50 map<long,int> nCount;
51 int ntotal(0);
52 for (const Particle& p: fs.particles()) {
53 nCount[p.pid()] += 1;
54 ++ntotal;
55 }
56 const FinalState& ufs = apply<FinalState>(event, "UFS");
57 // find the psis
58 for (const Particle& p : ufs.particles(Cuts::pid==443)) {
59 if (p.children().empty()) continue;
60 map<long,int> nRes = nCount;
61 int ncount = ntotal;
62 findChildren(p,nRes,ncount);
63 // psi pi+pi-
64 if (ncount!=2) continue;
65 bool matched = true;
66 for (const auto& val : nRes) {
67 if (abs(val.first)==310) {
68 if (val.second !=2) {
69 matched = false;
70 break;
71 }
72 }
73 else if (val.second!=0) {
74 matched = false;
75 break;
76 }
77 }
78 if (matched) {
79 _sigmaPsi->fill(_ecms);
80 break;
81 }
82 }
83 }
84
85
86 /// Normalise histograms etc., after the run
87 void finalize() {
88 scale(_sigmaPsi,crossSection()/ sumOfWeights() /picobarn);
89 }
90
91 /// @}
92
93
94 /// @name Histograms
95 /// @{
96 BinnedHistoPtr<string> _sigmaPsi;
97 string _ecms;
98 /// @}
99
100
101 };
102
103
104 RIVET_DECLARE_PLUGIN(BESIII_2022_I2182758);
105
106}
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