Rivet analyses referenceBESIII_2021_I1880103Cross Section for $e^+e^-\to\gamma\chi_{c(1,2)}$ for energies between 3.773 and 4.600 GeVExperiment: BESIII () Inspire ID: 1880103 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); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3) GeV Run details:
Cross section for $e^+e^-\to\gamma\chi_{c(1,2)}$ for energies between 3.773 and 4.600 GeV measured by the BESIII collaboration. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2021_I1880103.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- > gamma chi_c(1,2)
10 class BESIII_2021_I1880103 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1880103);
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(Cuts::pid==20443 || Cuts::pid==445), "UFS");
24 for (unsigned int ix=0; ix<2; ++ix) {
25 book(_sigmaChi[ix], 1+ix, 1, 1);
26 }
27
28 for (const string& en : _sigmaChi[0].binning().edges<0>()) {
29 const double end = std::stod(en)*GeV;
30 if (isCompatibleWithSqrtS(end)) {
31 _ecms = en;
32 break;
33 }
34 }
35 if (_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
36 }
37
38 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
39 for (const Particle &child : p.children()) {
40 if (child.children().empty()) {
41 --nRes[child.pid()];
42 --ncount;
43 }
44 else {
45 findChildren(child,nRes,ncount);
46 }
47 }
48 }
49
50 /// Perform the per-event analysis
51 void analyze(const Event& event) {
52 const FinalState& fs = apply<FinalState>(event, "FS");
53 map<long,int> nCount;
54 int ntotal(0);
55 for (const Particle& p : fs.particles()) {
56 nCount[p.pid()] += 1;
57 ++ntotal;
58 }
59 const FinalState& ufs = apply<FinalState>(event, "UFS");
60 for (const Particle& p : ufs.particles()) {
61 if (p.children().empty()) continue;
62 // find the chi_c
63 map<long,int> nRes = nCount;
64 int ncount = ntotal;
65 findChildren(p,nRes,ncount);
66 bool matched=true;
67 if (ncount!=1) continue;
68 for (const auto& val : nRes) {
69 if (val.first==PID::PHOTON) {
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 if (p.pid()==20443) {
82 _sigmaChi[0]->fill(_ecms);
83 }
84 else {
85 _sigmaChi[1]->fill(_ecms);
86 }
87 break;
88 }
89 }
90 }
91
92
93 /// Normalise histograms etc., after the run
94 void finalize() {
95 scale(_sigmaChi, crossSection()/ sumOfWeights() /picobarn);
96 }
97
98 /// @}
99
100
101 /// @name Histograms
102 /// @{
103 BinnedHistoPtr<string> _sigmaChi[2];
104 string _ecms;
105 /// @}
106
107
108 };
109
110
111 RIVET_DECLARE_PLUGIN(BESIII_2021_I1880103);
112
113}
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