Rivet analyses referenceBESIII_2016_I1495838Cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.77 and 4.6 GeVExperiment: BESIII (BEPC) Inspire ID: 1495838 Status: VALIDATED Authors:
Beam energies: (1.9, 1.9); (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); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (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); (2.1, 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); (2.1, 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); (2.2, 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) GeV Run details:
Measurement of the cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.77 and 4.6 GeV. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2016_I1495838.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 Cross section for $e^+e^-\to J/\psi\pi^+\pi^-$ at energies between 3.77 and 4.6 GeV
10 class BESIII_2016_I1495838 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1495838);
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 for(unsigned int ix=0;ix<2;++ix) {
25 book(_sigmaPsi[ix], 1+ix, 1, 1);
26 for (const string& en : _sigmaPsi[ix].binning().edges<0>()) {
27 const double end = std::stod(en)*GeV;
28 if (isCompatibleWithSqrtS(end)) {
29 _ecms[ix] = en;
30 break;
31 }
32 }
33 }
34 if (_ecms[0].empty() && _ecms[1].empty()) {
35 MSG_ERROR("Beam energy incompatible with analysis.");
36 }
37 }
38
39 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
40 for (const Particle &child : p.children()) {
41 if(child.children().empty()) {
42 --nRes[child.pid()];
43 --ncount;
44 }
45 else
46 findChildren(child,nRes,ncount);
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 // find the psis
61 for (const Particle& p : ufs.particles(Cuts::pid==443)) {
62 if(p.children().empty()) continue;
63 map<long,int> nRes = nCount;
64 int ncount = ntotal;
65 findChildren(p,nRes,ncount);
66 // psi pi+pi-
67 if(ncount!=2) continue;
68 bool matched = true;
69 for(auto const & val : nRes) {
70 if(abs(val.first)==211) {
71 if(val.second !=1) {
72 matched = false;
73 break;
74 }
75 }
76 else if(val.second!=0) {
77 matched = false;
78 break;
79 }
80 }
81 if(matched) {
82 _sigmaPsi[0]->fill(_ecms[0]);
83 _sigmaPsi[1]->fill(_ecms[1]);
84 break;
85 }
86 }
87 }
88
89 /// Normalise histograms etc., after the run
90 void finalize() {
91 double fact = crossSection()/ sumOfWeights() /picobarn;
92 for(unsigned int ix=0;ix<2;++ix)
93 scale(_sigmaPsi[ix],fact);
94 }
95
96 /// @}
97
98
99 /// @name Histograms
100 /// @{
101 BinnedHistoPtr<string> _sigmaPsi[2];
102 string _ecms[2];
103 /// @}
104
105
106 };
107
108
109
110 RIVET_DECLARE_PLUGIN(BESIII_2016_I1495838);
111
112}
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