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BESIII_2022_I2135117

Mass and angluar distributions in $J/\psi\to\gamma\eta\eta^\prime$
Experiment: BESIII (BEPC)
Inspire ID: 2135117
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 106 (2022) 7, 072012
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing J/psi, originally e+e-

Measurement of mass and angluar distributions in $J/\psi\to\gamma\eta\eta^\prime$ by BESIII. The background subtracted data were read from the plots in the paper.

Source code: BESIII_2022_I2135117.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 J/psi -> gamma eta eta'
10  class BESIII_2022_I2135117 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2135117);
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::abspid==443);
24      declare(ufs, "UFS");
25      DecayedParticles PSI(ufs);
26      PSI.addStable(PID::ETA);
27      PSI.addStable(PID::ETAPRIME);
28      declare(PSI, "PSI");
29      // histos
30      for(unsigned int ix=0;ix<3;++ix) {
31	book(_h_angle[ix],2,1,1+ix);
32	book(_h_mass [ix],1,1,1+ix);
33      }
34      book(_h_angle[3],1,1,4);
35    }
36
37
38    /// Perform the per-event analysis
39    void analyze(const Event& event) {
40      // find the J/psi decays
41      static const map<PdgId,unsigned int> & mode = { { 22,1},{ 221,1},{ 331,1}};
42      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
43      for(unsigned int ix=0;ix<PSI.decaying().size();++ix) {
44	if(!PSI.modeMatches(ix,3,mode)) continue;
45	const Particle  & eta  = PSI.decayProducts()[ix].at(221)[0];
46	const Particle  & etap = PSI.decayProducts()[ix].at(331)[0];
47	const Particle  & gam  = PSI.decayProducts()[ix].at( 22)[0];
48	double mEE = (eta.momentum()+etap.momentum()).mass();
49	double mEG = (gam.momentum()+eta .momentum()).mass();
50	if(abs(mEG-1.019461)<0.04) continue;
51	_h_mass[0]->fill(mEE);
52	_h_mass[1]->fill(mEG);
53	_h_mass[2]->fill((gam.momentum()+etap.momentum()).mass());
54	// angles
55	LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
56	FourMomentum pGamma = boost1.transform(gam.momentum());
57	FourMomentum pEE    = boost1.transform(eta.momentum()+etap.momentum());
58	LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pEE.betaVec());
59	Vector3 axis2 = boost2.transform(boost1.transform(eta.momentum())).p3().unit();
60	double cTheta = pGamma.p3().unit().dot(axis2);
61	_h_angle[3]->fill(cTheta);
62	if( mEE>1.5 && mEE<1.7)
63	  _h_angle[0]->fill(cTheta);
64	else if(mEE>1.7 && mEE<2.)
65	  _h_angle[1]->fill(cTheta);
66	else if(mEE>2. && mEE<3.2)
67	  _h_angle[2]->fill(cTheta);
68      }
69    }
70
71
72    /// Normalise histograms etc., after the run
73    void finalize() {
74      for(unsigned int ix=0;ix<4;++ix) {
75	normalize(_h_angle[ix],1.,false);
76	if(ix<3) normalize(_h_mass[ix],1.,false);
77      }
78    }
79
80    /// @}
81
82
83    /// @name Histograms
84    /// @{
85    Histo1DPtr _h_mass[3],_h_angle[4];
86    /// @}
87  };
88
89
90  RIVET_DECLARE_PLUGIN(BESIII_2022_I2135117);
91
92}