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MC_DECAY_ETA

Analysis of Kinematic distributions in $\eta$ and $\eta^\prime$ meson decays
Experiment: ()
Status: VALIDATED
Authors:
  • Peter Richardson
No references listed
Beams: * *
Beam energies: ANY
Run details:
  • Any type of process producing eta/eta prime mesons

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}