Rivet analyses referenceBESIII_2014_I1287631$e^+e^-$ mass distribution in $J/\psi\to e^+e^-$ $+\eta^\prime,$ $\eta$ or $\pi^0$Experiment: BESIII (BEPC) Inspire ID: 1287631 Status: VALIDATED NOHEPDATA Authors:
Beam energies: ANY Run details:
$e^+e^-$ mass distribution in $J/\psi\to e^+e^-$ $+\eta^\prime,$ $\eta$ or $\pi^0$. Data read from plots in paper.Mass distributions are not efficiency corrected. Source code: BESIII_2014_I1287631.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 -> eta', eta, pi0 e+e-
10 class BESIII_2014_I1287631 : public Analysis {
11 public:
12
13 /// Constructor
14 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2014_I1287631);
15
16
17 /// @name Analysis methods
18 /// @{
19
20 /// Book histograms and initialise projections before the run
21 void init() {
22 UnstableParticles ufs = UnstableParticles(Cuts::abspid==PID::JPSI);
23 declare(ufs, "UFS");
24 DecayedParticles psi(ufs);
25 psi.addStable(PID::PI0);
26 psi.addStable(PID::ETA);
27 psi.addStable(PID::ETAPRIME);
28 declare(psi, "PSI");
29 for(unsigned int ix=0;ix<5;++ix)
30 book(_h[ix], 1, 1, ix+1);
31 book(_h[5],2,1,1);
32 book(_c,"TMP/den");
33 }
34
35
36 /// Perform the per-event analysis
37 void analyze(const Event& event) {
38 // define the decay mode
39 static const map<PdgId,unsigned int> & mode0 = { {PID::ETAPRIME,1},{ PID::PHOTON,1} };
40 static const map<PdgId,unsigned int> & mode1 = { {PID::ETAPRIME,1},{ 11,1}, { -11,1}};
41 static const map<PdgId,unsigned int> & mode2 = { {PID::ETA ,1},{ 11,1}, { -11,1}};
42 static const map<PdgId,unsigned int> & mode3 = { {PID::PI0 ,1},{ 11,1}, { -11,1}};
43 DecayedParticles psi = apply<DecayedParticles>(event, "PSI");
44 // loop over particles
45 for(unsigned int ix=0;ix<psi.decaying().size();++ix) {
46 unsigned int imode=0;
47 if(psi.modeMatches(ix,2,mode0)) {
48 _c->fill();
49 continue;
50 }
51 else if(psi.modeMatches(ix,3,mode1)) {
52 imode=1;
53 }
54 else if(psi.modeMatches(ix,3,mode2)) {
55 imode=2;
56 }
57 else if(psi.modeMatches(ix,3,mode3)) {
58 imode=3;
59 }
60 else
61 continue;
62 // e+ e-
63 const Particle & em = psi.decayProducts()[ix].at( 11)[0];
64 const Particle & ep = psi.decayProducts()[ix].at(-11)[0];
65 double q = (ep.momentum()+em.momentum()).mass();
66 if(imode==1) {
67 _h[0]->fill(q);
68 _h[1]->fill(q);
69 double me = em.mass();
70 double beta = sqrt(1.-4.*sqr(me/q));
71 double mJpsi = psi.decaying()[ix].mass();
72 double mEta = psi.decayProducts()[ix].at(331)[0].mass();
73 double p = sqrt(sqr(1.+sqr(q)/(sqr(mJpsi)-sqr(mEta)))-4.*sqr(mJpsi*q/(sqr(mJpsi)-sqr(mEta))));
74 double fact = beta*GeV/q*(1.+2.*sqr(me/q))*pow(p,3);
75 _h[5]->fill(q,1./fact);
76 }
77 else if(imode==2) {
78 _h[2]->fill(q);
79 _h[3]->fill(q);
80 }
81 else {
82 _h[4]->fill(q);
83 }
84 }
85 }
86
87
88 /// Normalise histograms etc., after the run
89 void finalize() {
90 for(unsigned int ix=0;ix<5;++ix)
91 normalize(_h[ix],1.,false);
92 static double alpha= 7.2973525664e-3;
93 scale(_h[5], 1.5 *M_PI/alpha/ *_c);
94 }
95
96 /// @}
97
98
99 /// @name Histograms
100 /// @{
101 Histo1DPtr _h[6];
102 CounterPtr _c;
103 /// @}
104
105
106 };
107
108
109 RIVET_DECLARE_PLUGIN(BESIII_2014_I1287631);
110
111}
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