Rivet analyses referenceBESIII_2018_I1646687Mass and angular distributions in $J/\psi\to\gamma\gamma\phi$Experiment: BESIII (BEPC) Inspire ID: 1646687 Status: VALIDATED NOHEPDATA Authors:
Beam energies: (1.6, 1.6) GeV Run details:
Mass and angulr distributions in the decay $J/\psi\to\gamma\gamma\phi$ Source code: BESIII_2018_I1646687.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/Beam.hh"
4#include "Rivet/Projections/UnstableParticles.hh"
5#include "Rivet/Projections/DecayedParticles.hh"
6
7namespace Rivet {
8
9
10 /// @brief Jpsi -> gamma gamma phi
11 class BESIII_2018_I1646687 : public Analysis {
12 public:
13
14 /// Constructor
15 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1646687);
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 UnstableParticles ufs = UnstableParticles(Cuts::abspid==443);
25 declare(ufs, "UFS");
26 DecayedParticles PSI(ufs);
27 PSI.addStable(PID::PHI);
28 declare(PSI, "PSI");
29 declare(Beam(), "Beams");
30 book(_h_mass,1,1,1);
31 for(unsigned int ix=0;ix<2;++ix) {
32 book(_h_angle[ix],2,1,1+ix);
33 }
34 }
35
36
37 /// Perform the per-event analysis
38 void analyze(const Event& event) {
39 // get the axis, direction of incoming electron
40 const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
41 Vector3 axis;
42 if(beams.first.pid()>0)
43 axis = beams.first .momentum().p3().unit();
44 else
45 axis = beams.second.momentum().p3().unit();
46 // find the J/psi decays
47 static const map<PdgId,unsigned int> & mode = { { 22,2},{ 333,1}};
48 DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
49 if( PSI.decaying().size()!=1) vetoEvent;
50 if(!PSI.modeMatches(0,3,mode)) vetoEvent;
51 // particles
52 const Particle & phi = PSI.decayProducts()[0].at(333)[0];
53 const Particles & gam = PSI.decayProducts()[0].at( 22);
54 for(unsigned int ix=0;ix<2;++ix) {
55 double mPhiGamma = (gam[ix].momentum()+phi.momentum()).mass();
56 _h_mass->fill(mPhiGamma);
57 double cTheta = axis.dot(gam[ix==0 ? 1 : 0].p3().unit());
58 if(mPhiGamma>1.4 && mPhiGamma<1.6)
59 _h_angle[0]->fill(cTheta);
60 else if(mPhiGamma>1.75 && mPhiGamma<1.9)
61 _h_angle[1]->fill(cTheta);
62 }
63 }
64
65
66 /// Normalise histograms etc., after the run
67 void finalize() {
68 normalize(_h_mass,1.,false);
69 for(unsigned int ix=0;ix<2;++ix) {
70 normalize(_h_angle[ix],1.,false);
71 }
72 }
73
74 /// @}
75
76
77 /// @name Histograms
78 /// @{
79 Histo1DPtr _h_mass, _h_angle[2];
80 /// @}
81
82
83 };
84
85
86 RIVET_DECLARE_PLUGIN(BESIII_2018_I1646687);
87
88}
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