Rivet analyses referenceBABAR_2018_I1691222$e^+e^-\to e^+e^-\eta^\prime$ via intermediate photons at 10.58 GeVExperiment: BABAR (PEP-II) Inspire ID: 1691222 Status: VALIDATED Authors:
Beam energies: (5.3, 5.3) GeV Run details:
Measurement of the cross section for the production of $\eta^\prime$ in photon-photon collisions, i.e. $e^+e^-\to \gamma\gamma e^+e^-$ followed by $\gamma\gamma\to\eta^\prime$, by the Babar experiment at 10.58 GeV. This measurement is doubly differential in the virtuality of the two photons. Source code: BABAR_2018_I1691222.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/FinalState.hh"
4#include "Rivet/Projections/UnstableParticles.hh"
5#include "Rivet/Projections/Beam.hh"
6
7namespace Rivet {
8
9
10 /// @brief e+e- > e+e- eta'
11 class BABAR_2018_I1691222 : public Analysis {
12 public:
13
14 /// Constructor
15 RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2018_I1691222);
16
17
18 /// @name Analysis methods
19 ///@{
20
21 /// Book histograms and initialise projections before the run
22 void init() {
23 // Initialise and register projections
24 declare(Beam(), "Beams");
25 declare(FinalState(),"FS");
26 declare(UnstableParticles(), "UFS");
27 // book the histograms
28 book(_h_etap,1,1,1);
29 }
30
31 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
32 for (const Particle &child : p.children()) {
33 if (child.children().empty()) {
34 --nRes[child.pid()];
35 --ncount;
36 } else {
37 findChildren(child,nRes,ncount);
38 }
39 }
40 }
41
42 bool findScattered(Particle beam, double& q2) {
43 bool found = false;
44 Particle scat = beam;
45 while (!scat.children().empty()) {
46 found = false;
47 for (const Particle & p : scat.children()) {
48 if (p.pid()==scat.pid()) {
49 scat=p;
50 found=true;
51 break;
52 }
53 }
54 if (!found) break;
55 }
56 if (!found) return false;
57 q2 = -(beam.momentum() - scat.momentum()).mass2();
58 return true;
59 }
60
61 /// Perform the per-event analysis
62 void analyze(const Event& event) {
63 if(_edges.empty()) _edges = _h_etap->xEdges();
64 // find scattered leptons and calc Q2
65 const Beam& beams = apply<Beam>(event, "Beams");
66 double q12 = -1, q22 = -1;
67 if (!findScattered(beams.beams().first, q12)) vetoEvent;
68 if (!findScattered(beams.beams().second, q22)) vetoEvent;
69 if(q22>q12) swap(q12,q22);
70 // check the final state
71 const FinalState & fs = apply<FinalState>(event, "FS");
72 map<long,int> nCount;
73 int ntotal(0);
74 for (const Particle& p : fs.particles()) {
75 nCount[p.pid()] += 1;
76 ++ntotal;
77 }
78 // find the meson
79 const FinalState& ufs = apply<FinalState>(event, "UFS");
80 for (const Particle& p : ufs.particles(Cuts::pid==331)) {
81 if(p.children().empty()) continue;
82 map<long,int> nRes = nCount;
83 int ncount = ntotal;
84 findChildren(p,nRes,ncount);
85 bool matched = true;
86 for(auto const & val : nRes) {
87 if(abs(val.first)==11) {
88 if(val.second!=1) {
89 matched = false;
90 break;
91 }
92 }
93 else if(val.second!=0) {
94 matched = false;
95 break;
96 }
97 }
98 if (matched) {
99 // 2<Q2<10 for both photons bin
100 if(q12>2.&&q12<10.&&q22>2.&&q22<10.) {
101 _h_etap->fill(_edges[0],1./sqr(8.));
102 }
103 // 10<Q2<30 for both photons bin
104 else if(q12>10&&q12<30.&&q22>10.&&q22<30.)
105 _h_etap->fill(_edges[1],1./sqr(20.));
106 // 10<Q12<30 2<Q22<10
107 else if(q22>2.&&q22<10.&&q12>10.&&q12<30.)
108 _h_etap->fill(_edges[2],1./8./20./2.);
109 // 2<Q22<30 30<Q12<60
110 else if(q22>2.&&q22<30.&&q12>30.&&q12<60.)
111 _h_etap->fill(_edges[3],1./28./30./2.);
112 // 30<Q2<60 for both photons
113 else if(q22>30.&&q22<60.&&q12>30.&&q12<60.)
114 _h_etap->fill(_edges[4],1./sqr(30.));
115 }
116 }
117 }
118
119 /// Normalise histograms etc., after the run
120 void finalize() {
121 scale(_h_etap, 1e4*crossSection()/femtobarn/sumW());
122 }
123
124 ///@}
125
126
127 /// @name Histograms
128 ///@{
129 BinnedHistoPtr<string> _h_etap;
130 vector<string> _edges;
131 ///@}
132
133
134 };
135
136
137 RIVET_DECLARE_PLUGIN(BABAR_2018_I1691222);
138
139}
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