Rivet analyses referenceBESIII_2016_I1504943$\eta^\prime \to\gamma\gamma\pi^0$ decaysExperiment: BESIII (BEPC) Inspire ID: 1504943 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
Measurement of the $\gamma\gamma$ mass distribution in the $\eta^\prime \to\gamma\gamma\pi^0$ decay by the BESIII collaboration. Source code: BESIII_2016_I1504943.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4#include "Rivet/Projections/DecayedParticles.hh"
5
6namespace Rivet {
7
8
9 /// @brief eta' -> gamma gamma pi0
10 class BESIII_2016_I1504943 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1504943);
15
16
17 /// @name Analysis methods
18 /// @{
19
20 /// Book histograms and initialise projections before the run
21 void init() {
22 // Initialise and register projections
23 UnstableParticles ufs = UnstableParticles(Cuts::pid==331);
24 declare(ufs, "UFS");
25 DecayedParticles ETA(ufs);
26 ETA.addStable(PID::PI0);
27 ETA.addStable(PID::K0S);
28 declare(ETA, "ETA");
29 // Book histograms
30 for(unsigned int ix=0;ix<3;++ix)
31 book(_h_br[ix],1,1,1+ix);
32 book(_h_m, 2, 1, 1);
33 book(_netap, "TMP/netap");
34 }
35
36 /// Perform the per-event analysis
37 void analyze(const Event& event) {
38 static const map<PdgId,unsigned int> & mode = { {111,1}, { 22,2} };
39 DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
40 // loop over particles
41 for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
42 _netap->fill();
43 // select right decay mode
44 if ( !ETA.modeMatches(ix,3,mode)) continue;
45 const Particles & gam = ETA.decayProducts()[ix].at(22);
46 double mass2 = (gam[0].momentum()+gam[1].momentum()).mass2();
47 _h_m->fill(mass2);
48 _h_br[0]->fill(.5);
49 if(any(ETA.decaying()[ix].children(), hasAbsPID(PID::OMEGA))) _h_br[1]->fill(.5);
50 if(ETA.decaying()[ix].children().size()==3) _h_br[2]->fill(0.5);
51 }
52 }
53
54
55 /// Normalise histograms etc., after the run
56 void finalize() {
57 // eta' width in kev
58 double gammaEtap = 0.188e3;
59 scale(_h_m, gammaEtap/ *_netap);
60 for(unsigned int ix=0;ix<3;++ix)
61 scale(_h_br[ix], 1e4/ *_netap);
62 }
63
64 /// @}
65
66
67 /// @name Histograms
68 /// @{
69 Histo1DPtr _h_m,_h_br[3];
70 CounterPtr _netap;
71 /// @}
72
73
74 };
75
76
77 RIVET_DECLARE_PLUGIN(BESIII_2016_I1504943);
78
79}
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