Rivet analyses referenceMC_DECAY_ETAAnalysis of Kinematic distributions in $\eta$ and $\eta^\prime$ meson decaysExperiment: () Status: VALIDATED Authors:
Beams: * * Beam energies: ANY Run details:
Analysis of Kinematic distributions in $\eta$ and $\eta^\prime$ meson decays. The mass distributions in the decays $\eta,\eta^\prime\to \gamma\pi^+\pi^-$, $\gamma\gamma\pi^0$, $\pi^0\pi^0\pi^0$, $\pi^+\pi^-\pi^0$ and $\eta^\prime\to\pi^+\pi^-\eta$, $\pi^0\pi^0\eta$ are produced. Based on an +old Herwig++ internal analysis. Source code: MC_DECAY_ETA.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/UnstableParticles.hh"
4
5namespace Rivet {
6
7
8 class MC_DECAY_ETA : public Analysis {
9 public:
10
11 /// Constructor
12 RIVET_DEFAULT_ANALYSIS_CTOR(MC_DECAY_ETA);
13
14
15 /// @name Analysis methods
16 /// @{
17
18 /// Book histograms and initialise projections before the run
19 void init() {
20
21 // Initialise and register projections
22 declare(UnstableParticles(), "UFS");
23
24 // Book histograms
25 double meta[2]={547.45, 957.78};
26 for(unsigned int ix=0;ix<2;++ix) {
27 std::ostringstream title; title << "_" << ix;
28 _mgammagamma.push_back(Histo1DPtr());
29 book(_mgammagamma.back(), "mgammagamma" +title.str(),200,0.,meta[ix]);
30 _mpi0gamma.push_back(Histo1DPtr());
31 book(_mpi0gamma.back(), "mpi0gamma" +title.str(),200,0.,meta[ix]);
32 _mpipgamma.push_back(Histo1DPtr());
33 book(_mpipgamma.back(), "mpipgamma" +title.str(),200,0.,meta[ix]);
34 _mpimgamma.push_back(Histo1DPtr());
35 book(_mpimgamma.back(), "mpimgamma" +title.str(),200,0.,meta[ix]);
36 _photonenergy.push_back(Histo1DPtr());
37 book(_photonenergy.back(), "photonenergy"+title.str(),200,0.,meta[ix]);
38 _mpippim.push_back(Histo1DPtr());
39 book(_mpippim.back(), "mpippim" +title.str(),200,0.,meta[ix]);
40 _dpippim.push_back(Histo1DPtr());
41 book(_dpippim.back(), "dpippim" +title.str(),200,200.,meta[ix]);
42 _dpi0pi0.push_back(Histo1DPtr());
43 book(_dpi0pi0.back(), "dpi0pi0" +title.str(),200,200.,meta[ix]);
44 _dpi0pip.push_back(Histo1DPtr());
45 book(_dpi0pip.back(), "dpi0pip" +title.str(),200,200.,meta[ix]);
46 _dpi0pim.push_back(Histo1DPtr());
47 book(_dpi0pim.back(), "dpi0pim" +title.str(),200,200.,meta[ix]);
48 }
49 _dpi0pi0.push_back(Histo1DPtr());
50 book(_dpi0pi0.back(), "dpi0pi0_2",200,200.,500. );
51 _dpippim.push_back(Histo1DPtr());
52 book(_dpippim.back(), "dpippim_2",200,200.,500. );
53 book(_dpipeta, "dpipeta",200,500.,meta[1]) ;
54 book(_dpimeta, "dpimeta",200,500.,meta[1]) ;
55 book(_dpi0eta, "dpi0eta",200,500.,meta[1]) ;
56 }
57
58 void findDecayProducts(const Particle & mother,
59 unsigned int & nstable,
60 Particles& pip, Particles& pim,
61 Particles& pi0, Particles& eta,
62 Particles& gamma) {
63 for(const Particle & p : mother.children()) {
64 int id = p.pid();
65 if ( id == PID::ETA ) {
66 eta.push_back(p);
67 ++nstable;
68 }
69 else if ( id == PID::PHOTON ) {
70 gamma.push_back(p);
71 ++nstable;
72 }
73 else if (id == PID::PIPLUS) {
74 pip.push_back(p);
75 ++nstable;
76 }
77 else if (id == PID::PIMINUS) {
78 pim.push_back(p);
79 ++nstable;
80 }
81 else if (id == PID::PI0 ) {
82 pi0.push_back(p);
83 ++nstable;
84 }
85 else if (id == PID::K0S || id == PID::K0L ||
86 id == PID::KPLUS || id == PID::KMINUS)
87 ++nstable;
88 else if ( !p.children().empty() ) {
89 findDecayProducts(p,nstable,pip,pim,pi0,eta,gamma);
90 }
91 else
92 ++nstable;
93 }
94 }
95
96 /// Perform the per-event analysis
97 void analyze(const Event& event) {
98 // Loop over f_1 mesons
99 for(const Particle& meson : apply<UnstableParticles>(event, "UFS").
100 particles(Cuts::pid==221||Cuts::pid==331)) {
101 unsigned int nstable(0);
102 Particles pip, pim, pi0, eta, gamma;
103 findDecayProducts(meson,nstable,pip, pim, pi0, eta, gamma);
104 unsigned int imeson = meson.pid()==221 ? 0 : 1;
105 // pi0 gamma gamma
106 if(nstable==3 && pi0.size()==1 && gamma.size()==2) {
107 _mgammagamma[imeson]->fill((gamma[0].momentum()+gamma[1].momentum()).mass()/MeV);
108 _mpi0gamma [imeson]->fill(( pi0[0].momentum()+gamma[0].momentum()).mass()/MeV);
109 _mpi0gamma [imeson]->fill(( pi0[0].momentum()+gamma[1].momentum()).mass()/MeV);
110 } // pi+pi-gamma analysis
111 else if(nstable==3 && pip.size()==1 && pim.size()==1 && gamma.size()==1) {
112 FourMomentum ptemp = pip[0].momentum()+pim[0].momentum();
113 double mpipi = ptemp.mass();
114 _mpippim[imeson]->fill(mpipi/MeV);
115 double egamma = 0.5*(meson.mass()*meson.mass()-mpipi*mpipi)/meson.mass();
116 _photonenergy[imeson]->fill(egamma/MeV);
117 _mpipgamma[imeson]->fill((pip[0].momentum()+gamma[0].momentum()).mass()/MeV);
118 _mpimgamma[imeson]->fill((pim[0].momentum()+gamma[0].momentum()).mass()/MeV);
119 }
120 else if(nstable==3&& pi0.size()==3) {
121 _dpi0pi0[imeson]->fill((pi0[0].momentum()+pi0[1].momentum()).mass()/MeV);
122 _dpi0pi0[imeson]->fill((pi0[0].momentum()+pi0[2].momentum()).mass()/MeV);
123 _dpi0pi0[imeson]->fill((pi0[1].momentum()+pi0[2].momentum()).mass()/MeV);
124 }
125 else if(nstable==3&& pip.size()==1&&pim.size()==1&&pi0.size()==1) {
126 _dpi0pip[imeson]->fill((pi0[0].momentum()+pip[0].momentum()).mass()/MeV);
127 _dpi0pim[imeson]->fill((pi0[0].momentum()+pim[0].momentum()).mass()/MeV);
128 _dpippim[imeson]->fill((pip[0].momentum()+pim[0].momentum()).mass()/MeV);
129 }
130 else if(nstable==3&& pi0.size()==2&&eta.size()==1) {
131 _dpi0pi0[2]->fill((pi0[0].momentum()+pi0[1].momentum()).mass()/MeV);
132 _dpi0eta ->fill((pi0[0].momentum()+eta[0].momentum()).mass()/MeV);
133 _dpi0eta ->fill((pi0[1].momentum()+eta[0].momentum()).mass()/MeV);
134 }
135 else if(nstable==3&& pip.size()==1&&pim.size()==1&&eta.size()==1) {
136 _dpippim[2]->fill((pip[0].momentum()+pim[0].momentum()).mass()/MeV);
137 _dpipeta ->fill((pip[0].momentum()+eta[0].momentum()).mass()/MeV);
138 _dpimeta ->fill((pim[0].momentum()+eta[0].momentum()).mass()/MeV);
139 }
140 }
141 }
142
143
144 /// Normalise histograms etc., after the run
145 void finalize() {
146
147 // normalize to unity
148 for(unsigned int ix=0;ix<2;++ix) {
149 normalize(_mgammagamma[ix]);
150 normalize(_mpi0gamma[ix]);
151 normalize(_mpipgamma[ix]);
152 normalize(_mpimgamma[ix]);
153 normalize(_mpippim[ix]);
154 normalize(_photonenergy[ix]);
155 normalize(_dpippim[ix]);
156 normalize(_dpi0pi0[ix]);
157 normalize(_dpi0pip[ix]);
158 normalize(_dpi0pim[ix]);
159 }
160 normalize(_dpi0pi0[2]);
161 normalize(_dpippim[2]);
162 normalize(_dpipeta);
163 normalize(_dpimeta);
164 normalize(_dpi0eta);
165 }
166 /// @}
167
168
169 /**
170 * Histograms for the decay \f$\eta\to\pi^0\gamma\gamma\f$
171 */
172 /// @{
173 /**
174 * Histogram for the mass of \f$\gamma\gamma\f$
175 */
176 vector<Histo1DPtr> _mgammagamma;
177
178 /**
179 * Histogrma for the mass of \f$\pi^0\gamma\f$
180 */
181 vector<Histo1DPtr> _mpi0gamma;
182 /// @}
183
184 /**
185 * Histograms for the decay \f$\eta\to\pi^+\pi^-\gamma\f$
186 */
187 /// @{
188 /**
189 * Histogram for the mass of \f$\pi^+\gamma\f$
190 */
191 vector<Histo1DPtr> _mpipgamma;
192
193 /**
194 * Histogram for the mass of \f$\pi^-\gamma\f$
195 */
196 vector<Histo1DPtr> _mpimgamma;
197
198 /**
199 * Histogram for the mass of \f$\pi^+\pi^-\f$
200 */
201 vector<Histo1DPtr> _mpippim;
202
203 /**
204 * Histogram for the photon energy
205 */
206 vector<Histo1DPtr> _photonenergy;
207 /// @}
208
209 /**
210 * Histograms for the decay \f$\eta\pi\pi\pi\f$ and \f$\eta'\to\eta\pi\pi\f$.
211 */
212 /// @{
213 /**
214 * Histogram for the mass of \f$\pi^+\pi^-\f$
215 */
216 vector<Histo1DPtr> _dpippim;
217
218 /**
219 * Histogram for the mass of \f$\pi^0\pi^0\f$
220 */
221 vector<Histo1DPtr> _dpi0pi0;
222
223 /**
224 * Histogram for the mass of \f$\pi^0\pi^+\f$
225 */
226 vector<Histo1DPtr> _dpi0pip;
227
228 /**
229 * Histogram for the mass of \f$\pi^0\pi^-\f$
230 */
231 vector<Histo1DPtr> _dpi0pim;
232
233 /**
234 * Histogram for the mass of \f$\pi^+\eta\f$
235 */
236 Histo1DPtr _dpipeta;
237
238 /**
239 * Histogram for the mass of \f$\pi^-\eta\f$
240 */
241 Histo1DPtr _dpimeta;
242
243 /**
244 * Histogram for the mass of \f$\pi^0\eta\f$
245 */
246 Histo1DPtr _dpi0eta;
247 /// @}
248
249
250 };
251
252
253 RIVET_DECLARE_PLUGIN(MC_DECAY_ETA);
254
255}
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