Rivet analyses referenceBESIII_2015_I1377204Cross section for $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeVExperiment: BESIII (BEPC) Inspire ID: 1377204 Status: VALIDATED Authors:
Beam energies: ANY Run details:
Measurement of the cross section for $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeV Source code: BESIII_2015_I1377204.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 $e^+e^-\to J/\psi \pi^0\pi^0$ at energies between 4.19 and 4.42 GeV
10 class BESIII_2015_I1377204 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1377204);
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(_nJPsi, "TMP/jpsi");
25 }
26
27
28 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
29 for (const Particle &child : p.children()) {
30 if(child.children().empty()) {
31 --nRes[child.pid()];
32 --ncount;
33 }
34 else
35 findChildren(child,nRes,ncount);
36 }
37 }
38
39 /// Perform the per-event analysis
40 void analyze(const Event& event) {
41 const FinalState& fs = apply<FinalState>(event, "FS");
42 map<long,int> nCount;
43 int ntotal(0);
44 for (const Particle& p : fs.particles()) {
45 nCount[p.pid()] += 1;
46 ++ntotal;
47 }
48 const FinalState& ufs = apply<FinalState>(event, "UFS");
49 for (const Particle& p : ufs.particles()) {
50 if(p.children().empty()) continue;
51 // find the j/psi
52 if(p.pid()==443) {
53 map<long,int> nRes = nCount;
54 int ncount = ntotal;
55 findChildren(p,nRes,ncount);
56 // J/psi pi0pi0
57 if(ncount!=2) continue;
58 bool matched = true;
59 for(auto const & val : nRes) {
60 if(abs(val.first)==111) {
61 if(val.second !=2) {
62 matched = false;
63 break;
64 }
65 }
66 else if(val.second!=0) {
67 matched = false;
68 break;
69 }
70 }
71 if(matched) {
72 _nJPsi->fill();
73 break;
74 }
75 }
76 }
77 }
78
79
80 /// Normalise histograms etc., after the run
81 void finalize() {
82 double sigma = _nJPsi->val();
83 double error = _nJPsi->err();
84 sigma *= crossSection()/ sumOfWeights() /picobarn;
85 error *= crossSection()/ sumOfWeights() /picobarn;
86 Estimate1DPtr mult;
87 book(mult, 1, 1, 12);
88 for (auto& b : mult->bins()) {
89 if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
90 b.set(sigma, error);
91 }
92 }
93 }
94
95 /// @}
96
97
98 /// @name Histograms
99 /// @{
100 CounterPtr _nJPsi;
101 /// @}
102
103
104 };
105
106
107 RIVET_DECLARE_PLUGIN(BESIII_2015_I1377204);
108
109
110}
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