| Since the ccˉbound state of J/ψwas discovered in 1974, such asψ(2S),ψ(3770) andso on, have been subsequently discovered in experiment, and they are formed the charmo-nium family. Nowadays the measurements of their decays with large branching fractionsget more and more accurate, and thus provides us with a detailed evidence to understandtheir decay mechanisms and properties. For a J/ψproduced from e+e? annihilation,its decays into the baryon-antibaryon pair appears a specific angular distribution. Ex-perimental studies on the angular distribution will give us a plenty of knowledge aboutthe particle polarization, decay mechanisms, and shed light on the understanding of thestrong interactions. Especially, the decay of J/ψinto baryon-antibaryon pair is an ideallaboratory to study the violation of the helicity selection rule.In high energy physics experiments, the Monte-Carlo generators essential to do areliable simulation. According the energy scale to go or the specific process to use, eachexperiment collaboration designed their own event generators. In the upcoming comple-tion of the upgraded BESIII detector, the qualities of the Monte-Carlo event generatorsinstalled in the BOSS software is one of the most important key to achieve a reliabledetection e?ciency and systematic errors for doing accurate physics analysis. However,the most part of the available event generators at BESIII are constructed in the sense ofkinematical level. It is necessary to construct the event generator based on the dynami-cal information for charmonium decays, so that more dynamical e?ects and experimentaldetails are able to include in the event generators.To ensure that constructed event generator be able to describe the physics process asmuch as possible, one should pay more e?orts to study the decay mechanisms or model thedecay processes. For describing the charmonium decays mechanism, we can construct the transition amplitudes according to theirs respective process. The general way to constructtransition amplitude are covariant tensor method and helicity formalism. The helicityamplitude method allows one to construct the amplitude in a simple way, and allows oneto disentangle the angular distribution from the amplitude. For the generator models ofour building, we use the helicity formalism to construct all the transition amplitudes.Based on the above discussion, the main results of this work are as follows:1. Based on the Carimalo model, we calculate angular distributions for heavy quarko-nium decays into p Nˉ?(1440), decuplet baryon pairs, and octet-decuplet baryon pairs. Thegeneral formulae of angular distributions are explicitly given. And we discussed quarkmass e?ects in helicity violation in above decays. On the other hand, depending on theabove results, we build generator models for the charmonium decays into octet baryonpairs and decuplet baryon pairs in the framework of Monte Carlo event generator, Evt-Gen. Finally, we test them by looking for the baryon angular distribution. The fit valueαis well consistent with input value. Show our code is correct.2. For charmonium decays into octet-decuplet baryon pairs, we adopt the invari-ant N ? ? transition form factors that was developed by a Generalized-Vector-Meson-Dominance Model to build generator model. The generator model was test and the resultshows that the code is corrected code.3. We build a series of generator models for describing charmonium decaying intopseudoscalar meson pairs and vector meson pairs, as well asχcJ decaying into baryon-antibaryon pairs. Similarly, we construct the transition amplitudes with using the helicityformalism as done in precious decay mode. The results show the code are correted.4. For the decay J/ψ→γηc→γY Yˉ(Y :hyperon), we also construct the transitionamplitudes using the helicity formalism for decaysηc→ΛΛˉ,Σ0Σˉ0,Ξ?Ξˉ+, and presentthe angular distribution of these decays.
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