Rivet analyses referenceBESIII_2021_I1933191Cross section for e+e−→ψ(2S)π+π− at energies between 4.0 and 4.7 GeVExperiment: BESIII (BEPC) Inspire ID: 1933191 Status: VALIDATED Authors:
Beam energies: (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); (2.3, 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−→ψ(2S)π+π− at energies between 4.0 and 4.7 GeV by the BES collaboration. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2021_I1933191.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- > psi(2S) pi+pi-
10 class BESIII_2021_I1933191 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1933191);
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(_nPsi2s, 1, 1, 3);
25 for (const string& en : _nPsi2s.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()) 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 for (const Particle& p : ufs.particles()) {
58 if(p.children().empty()) continue;
59 // find the psi(2S)
60 if(p.pid()==100443) {
61 map<long,int> nRes = nCount;
62 int ncount = ntotal;
63 findChildren(p,nRes,ncount);
64 // omega pi+pi-
65 if(ncount!=2) continue;
66 bool matched = true;
67 for(auto const & val : nRes) {
68 if(abs(val.first)==211) {
69 if(val.second !=1) {
70 matched = false;
71 break;
72 }
73 }
74 else if(val.second!=0) {
75 matched = false;
76 break;
77 }
78 }
79 if(matched) {
80 _nPsi2s->fill(_ecms);
81 break;
82 }
83 }
84 }
85 }
86
87
88 /// Normalise histograms etc., after the run
89 void finalize() {
90 scale(_nPsi2s, crossSection()/ sumOfWeights() /picobarn);
91 }
92
93 ///@}
94
95
96 /// @name Histograms
97 ///@{
98 BinnedHistoPtr<string> _nPsi2s;
99 string _ecms;
100 ///@}
101
102
103 };
104
105
106 RIVET_DECLARE_PLUGIN(BESIII_2021_I1933191);
107
108}
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