Rivet analyses referenceBESIII_2022_I2163048Cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.773 and 4.7 GeVExperiment: BESIII (BEPC) Inspire ID: 2163048 Status: VALIDATED NOHEPDATA Authors:
Beam energies: (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (2.0, 2.0); (2.0, 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); (2.2, 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, 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); (2.3, 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) GeV Run details:
Measurement of the cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.773 and 4.7 GeV. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2022_I2163048.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- > pi+pi- J/psi
10 class BESIII_2022_I2163048 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2163048);
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 const double end = std::stod(en)*GeV;
27 if (isCompatibleWithSqrtS(end)) {
28 _ecms = en;
29 break;
30 }
31 }
32 if (_ecms.empty()) {
33 MSG_ERROR("Beam energy incompatible with analysis.");
34 }
35 }
36
37 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
38 for (const Particle &child : p.children()) {
39 if (child.children().empty()) {
40 --nRes[child.pid()];
41 --ncount;
42 }
43 else {
44 findChildren(child,nRes,ncount);
45 }
46 }
47 }
48
49 /// Perform the per-event analysis
50 void analyze(const Event& event) {
51 const FinalState& fs = apply<FinalState>(event, "FS");
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 const FinalState& ufs = apply<FinalState>(event, "UFS");
59 // find the psis
60 for (const Particle& p : ufs.particles(Cuts::pid==443)) {
61 if (p.children().empty()) continue;
62 map<long,int> nRes = nCount;
63 int ncount = ntotal;
64 findChildren(p,nRes,ncount);
65 // psi pi+pi-
66 if (ncount!=2) continue;
67 bool matched = true;
68 for (const auto& val : nRes) {
69 if (abs(val.first)==211) {
70 if (val.second !=1) {
71 matched = false;
72 break;
73 }
74 }
75 else if (val.second!=0) {
76 matched = false;
77 break;
78 }
79 }
80 if (matched) {
81 _sigmaPsi->fill(_ecms);
82 break;
83 }
84 }
85 }
86
87
88 /// Normalise histograms etc., after the run
89 void finalize() {
90 scale(_sigmaPsi, crossSection()/ sumOfWeights() /picobarn);
91 }
92
93 /// @}
94
95
96 /// @name Histograms
97 /// @{
98 BinnedHistoPtr<string> _sigmaPsi;
99 string _ecms;
100 /// @}
101
102
103 };
104
105
106 RIVET_DECLARE_PLUGIN(BESIII_2022_I2163048);
107
108}
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