Rivet analyses referenceSND_2000_I503946Cross section for $e^+e^-\to\omega\pi^0\to\pi^0\pi^0\gamma$ at energies near the $\phi$ mass.'Experiment: SND (VEPP-2M) Inspire ID: 503946 Status: VALIDATED Authors:
Beam energies: (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5) GeV Run details:
1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/FinalState.hh"
4#include "Rivet/Projections/UnstableParticles.hh"
5
6
7namespace Rivet {
8
9
10 /// @brief e+e- -> omega pi0
11 class SND_2000_I503946 : public Analysis {
12 public:
13
14 /// Constructor
15 RIVET_DEFAULT_ANALYSIS_CTOR(SND_2000_I503946);
16
17
18 /// @name Analysis methods
19 /// @{
20
21 /// Book histograms and initialise projections before the run
22 void init() {
23
24 // Initialise and register projections
25 declare(FinalState(), "FS");
26 declare(UnstableParticles(), "UFS");
27 book(_numOmegaPi, 1,1,1);
28 for (const string& en : _numOmegaPi.binning().edges<0>()) {
29 double end = std::stod(en)*MeV;
30 if(isCompatibleWithSqrtS(end)) {
31 _ecms = en;
32 break;
33 }
34 }
35 if(_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
36 }
37
38 void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
39 for (const Particle &child : p.children()) {
40 if(child.children().empty()) {
41 nRes[child.pid()]+=1;
42 ++ncount;
43 }
44 else
45 findChildren(child,nRes,ncount);
46 }
47 }
48
49 /// Perform the per-event analysis
50 void analyze(const Event& event) {
51 const FinalState& fs = apply<FinalState>(event, "FS");
52
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 // three particles (pi0 pi0 gamma)
60 if(ntotal!=3) vetoEvent;
61 const FinalState& ufs = apply<FinalState>(event, "UFS");
62 for (const Particle& p : ufs.particles()) {
63 if(p.children().empty()) continue;
64 // find the omega
65 if(p.pid()==223) {
66 map<long,int> nRes;
67 int ncount(0);
68 findChildren(p,nRes,ncount);
69 // only omega to pi0 gamma mode
70 if(ncount!=2) continue;
71 if(nRes[111]!=1 || nRes[22]!=1) continue;
72 // omega pi0
73 if(nCount[111]-nRes[111]==1)
74 _numOmegaPi->fill(_ecms);
75 }
76 }
77 }
78
79
80 /// Normalise histograms etc., after the run
81 void finalize() {
82 scale(_numOmegaPi, crossSection()/ sumOfWeights() /nanobarn);
83 }
84
85 /// @}
86
87
88 /// @name Histograms
89 /// @{
90 BinnedHistoPtr<string> _numOmegaPi;
91 string _ecms;
92 /// @}
93
94
95 };
96
97
98 RIVET_DECLARE_PLUGIN(SND_2000_I503946);
99
100
101}
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