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 // find scattered leptons and calc Q2
64 const Beam& beams = apply<Beam>(event, "Beams");
65 double q12 = -1, q22 = -1;
66 if (!findScattered(beams.beams().first, q12)) vetoEvent;
67 if (!findScattered(beams.beams().second, q22)) vetoEvent;
68 if(q22>q12) swap(q12,q22);
69 // check the final state
70 const FinalState & fs = apply<FinalState>(event, "FS");
71 map<long,int> nCount;
72 int ntotal(0);
73 for (const Particle& p : fs.particles()) {
74 nCount[p.pid()] += 1;
75 ++ntotal;
76 }
77 // find the meson
78 const FinalState& ufs = apply<FinalState>(event, "UFS");
79 for (const Particle& p : ufs.particles(Cuts::pid==331)) {
80 if(p.children().empty()) continue;
81 map<long,int> nRes = nCount;
82 int ncount = ntotal;
83 findChildren(p,nRes,ncount);
84 bool matched = true;
85 for(auto const & val : nRes) {
86 if(abs(val.first)==11) {
87 if(val.second!=1) {
88 matched = false;
89 break;
90 }
91 }
92 else if(val.second!=0) {
93 matched = false;
94 break;
95 }
96 }
97 if (matched) {
98 // 2<Q2<10 for both photons bin
99 if(q12>2.&&q12<10.&&q22>2.&&q22<10.) {
100 _h_etap->fill(0,1./sqr(8.));
101 }
102 // 10<Q2<30 for both photons bin
103 else if(q12>10&&q12<30.&&q22>10.&&q22<30.)
104 _h_etap->fill(1,1./sqr(20.));
105 // 10<Q12<30 2<Q22<10
106 else if(q22>2.&&q22<10.&&q12>10.&&q12<30.)
107 _h_etap->fill(2,1./8./20./2.);
108 // 2<Q22<30 30<Q12<60
109 else if(q22>2.&&q22<30.&&q12>30.&&q12<60.)
110 _h_etap->fill(3,1./28./30./2.);
111 // 30<Q2<60 for both photons
112 else if(q22>30.&&q22<60.&&q12>30.&&q12<60.)
113 _h_etap->fill(4,1./sqr(30.));
114 }
115 }
116 }
117
118 /// Normalise histograms etc., after the run
119 void finalize() {
120 scale(_h_etap, 1e4*crossSection()/femtobarn/sumW());
121 }
122
123 ///@}
124
125
126 /// @name Histograms
127 ///@{
128 Histo1DPtr _h_etap;
129 unsigned int _ncount=0;
130 ///@}
131
132
133 };
134
135
136 RIVET_DECLARE_PLUGIN(BABAR_2018_I1691222);
137
138}
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