Rivet analyses referenceBESIII_2014_I1258603Cross section for $e^+e^-\to\gamma X(3872)$ between 4.01 and 4.36 GeVExperiment: BESIII (BEPC) Inspire ID: 1258603 Status: VALIDATED NOHEPDATA Authors:
Beam energies: (2.0, 2.0); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2) GeV Run details:
Measurement of the cross section for $e^+e^-\to\gamma X(3872)$ times the branching ratio into the $J/\psi\pi^+\pi^-$ mode for $X(3872)$. There is no consensus as to the nature of the $X(3872)$ $c\bar{c}$ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one $c\bar{c}$ state. This can be changed using the PID option if a different code is used by the event generator performing the simulation. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2014_I1258603.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 X(3872)
10 class BESIII_2014_I1258603 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2014_I1258603);
15
16
17 /// @name Analysis methods
18 /// @{
19
20 /// Book histograms and initialise projections before the run
21 void init() {
22 // set the PDG code
23 _pid = getOption<double>("PID", 9030443);
24 // projections
25 declare(FinalState(), "FS");
26 declare(UnstableParticles(), "UFS");
27 // counters
28 book(_sigma,1,1,1);
29 for (const string& en : _sigma.binning().edges<0>()) {
30 const double end = std::stod(en)*GeV;
31 if (isCompatibleWithSqrtS(end)) {
32 _ecms = en;
33 break;
34 }
35 }
36 if (_ecms.empty()) {
37 MSG_ERROR("Beam energy incompatible with analysis.");
38 }
39 }
40
41 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
42 for (const Particle &child : p.children()) {
43 if (child.children().empty()) {
44 --nRes[child.pid()];
45 --ncount;
46 }
47 else {
48 findChildren(child,nRes,ncount);
49 }
50 }
51 }
52
53 /// Perform the per-event analysis
54 void analyze(const Event& event) {
55 const FinalState& fs = apply<FinalState>(event, "FS");
56 map<long,int> nCount;
57 int ntotal(0);
58 for (const Particle& p: fs.particles()) {
59 nCount[p.pid()] += 1;
60 ++ntotal;
61 }
62 const FinalState& ufs = apply<FinalState>(event, "UFS");
63 bool found = false;
64 for (const Particle & psi : ufs.particles(Cuts::pid==443)) {
65 if (psi.children().empty()) continue;
66 map<long,int> nRes = nCount;
67 int ncount = ntotal;
68 findChildren(psi,nRes,ncount);
69 // check for J/psi pi+pi- mode
70 if (ncount==3) {
71 bool matched = true;
72 for (const auto& val : nRes) {
73 if (abs(val.first)==211 || val.first==PID::GAMMA) {
74 if (val.second !=1) {
75 matched = false;
76 break;
77 }
78 }
79 else if (val.second!=0) {
80 matched = false;
81 break;
82 }
83 }
84 if (matched) {
85 found = true;
86 break;
87 }
88 }
89 }
90 if (!found) vetoEvent;
91 // find the intermediate
92 for (const Particle& XX : ufs.particles(Cuts::pid==_pid)) {
93 if (XX.children().empty()) continue;
94 map<long,int> nRes = nCount;
95 int ncount = ntotal;
96 findChildren(XX,nRes,ncount);
97 if (ncount!=1) continue;
98 bool matched = true;
99 for (const auto& val : nRes) {
100 if (val.first==PID::GAMMA) {
101 if (val.second !=1) {
102 matched = false;
103 break;
104 }
105 }
106 else if (val.second!=0) {
107 matched = false;
108 break;
109 }
110 }
111 if (matched) {
112 _sigma->fill(_ecms);
113 break;
114 }
115 }
116 }
117
118
119 /// Normalise histograms etc., after the run
120 void finalize() {
121 scale(_sigma,crossSection()/ sumOfWeights() /picobarn);
122 }
123
124 /// @}
125
126
127 /// @name Histograms
128 /// @{
129 int _pid;
130 BinnedHistoPtr<string> _sigma;
131 string _ecms;
132 /// @}
133
134
135 };
136
137
138 RIVET_DECLARE_PLUGIN(BESIII_2014_I1258603);
139
140}
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