Rivet analyses referenceKLOE2_2014_I1317236Form factor for the decay $\phi\to\eta e^+e^-$Experiment: KLOE2 (DAPHNE) Inspire ID: 1317236 Status: VALIDATED Authors:
Beam energies: ANY Run details:
Measurement of the form factor $\left|F_{\phi\eta }(q^2)\right|$ for the decay $\phi\to\eta e^+e^-$ by the KLOE experiment at DAPHNE Source code: KLOE2_2014_I1317236.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4
5namespace Rivet {
6
7
8 /// @brief form factor for phi-> eta
9 class KLOE2_2014_I1317236 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(KLOE2_2014_I1317236);
14
15
16 /// @name Analysis methods
17 /// @{
18
19 /// Book histograms and initialise projections before the run
20 void init() {
21 // Initialise and register projections
22 declare(UnstableParticles(), "UFS");
23 // Book histograms
24 book(_h_m, 1, 1, 1);
25 book(_weight,"TMP/weight");
26 }
27
28 void findDecayProducts(const Particle & mother, unsigned int & nstable, unsigned int & neta,
29 unsigned int & nep, unsigned int & nem, unsigned int & ngamma,
30 FourMomentum & ptot) {
31 for(const Particle & p : mother.children()) {
32 int id = p.pid();
33 if (id == PID::EMINUS ) {
34 ++nem;
35 ++nstable;
36 ptot += p.momentum();
37 }
38 else if (id == PID::EPLUS) {
39 ++nep;
40 ++nstable;
41 ptot += p.momentum();
42 }
43 else if (id == PID::ETA) {
44 ++neta;
45 ++nstable;
46 }
47 else if (id == PID::GAMMA) {
48 ++ngamma;
49 ++nstable;
50 }
51 else if ( !p.children().empty() ) {
52 findDecayProducts(p, nstable, neta,nep,nem,ngamma,ptot);
53 }
54 else
55 ++nstable;
56 }
57 }
58
59
60 /// Perform the per-event analysis
61 void analyze(const Event& event) {
62 static double me = 0.5109989461*MeV;
63 static double mphi = 1019.461*MeV;
64 static double meta = 547.862*MeV;
65
66 // Loop over phi mesons
67 for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==333)) {
68 unsigned nstable(0),neta(0),nep(0),nem(0),ngamma(0);
69 FourMomentum ptot;
70 findDecayProducts(p,nstable,neta,nep,nem,ngamma,ptot);
71 if(nstable==3 && nem==1 && nem==1 && neta==1) {
72 double q = ptot.mass();
73 double beta = sqrt(1.-4*sqr(me/q));
74 double p = sqrt(sqr(1.+sqr(q)/(sqr(mphi)-sqr(meta)))-4.*sqr(mphi*q/(sqr(mphi)-sqr(meta))));
75 double fact = beta*MeV/q*(1.+2.*sqr(me/q))*pow(p,3);
76 _h_m->fill(q/MeV,1./fact);
77 }
78 else if(nstable==2 && ngamma ==1 && neta==1) {
79 _weight->fill();
80 }
81 }
82 }
83
84
85 /// Normalise histograms etc., after the run
86 void finalize() {
87 static double alpha= 7.2973525664e-3;
88 scale(_h_m, 1.5*M_PI/alpha/ *_weight);
89 }
90
91 /// @}
92
93
94 /// @name Histograms
95 /// @{
96 Histo1DPtr _h_m;
97 CounterPtr _weight;
98 /// @}
99
100
101 };
102
103
104 RIVET_DECLARE_PLUGIN(KLOE2_2014_I1317236);
105
106
107}
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