Annihilation And Lifetime Of Antibaryon Bound In Nuclei

The modern nuclear structure is focusing on the properties of the unstable exotic nu-clear. As a special exotic nuclei, the properties of nuclei containing antibaryon(s) in additionto nucleons is an interesting topic in nuclear physics. This study is the crossing ?eld of nu-clear physics and particle physics. To estimate the lifetime and annihilation probability ofthe bound antibaryon further, it is desirable to investigate it based on a full quantum ?eldtheory. In this thesis, we proposed to study the the lifetime and annihilation process of thebound antibaryon in nuclei by using qunatum hadron dynamics. Based on the relativisticmean ?eld theory (RMF), with and without Dirac sea e?ect, we calculated the annihilationprobability and lifetime of deeply bound antinucleon embedded in system 16O + pˉ.In this thesis, the annihilation of bound state anti-nucleon was investigated in thefollowing aspects: the phase space of available energy in annihilation process, the averagedensity of nuclear medium, the strength of antibaryon-meson interaction, the annihilationcon?nement in high density zone of nuclear center. In addition, all possible initial state andall di?erent combination of ?nal state meson were considered into the following calculations:the annihilation probability of the anti-nucleon in di?erent channels, the branch ratios of?nal meson and average lifetime of the bound state anti-nucleon.First, the in?uence of phase space of available energy to annihilation was studied. Theannihilation probability is not increasing monotonically with the available energy phasespace. The annihilation probabilities of di?erent initial state distinct explicitly, the annihi-lation probabilities ofκp = ?1 initial state exceed the other initial states. And the branchratioπ,ω,ρmesons were in?uenced extraordinarily by the variation of available energy. Secondly, the in?uence of high nuclear density was investigated. Calculation showsthat the annihilation probability strongly depends on the e?ective mass of meson which wasgenerated in the annihilation channels. the contribution of the Dirac sea to the annihilationprobability makes the annihilation probability insensitive to the variation of energy spaceand nuclear density, and makes the lifetime of the antibaryon short. Without the Diracsea e?ect, the annihilation probability of antinucleon is very sensitive to nuclear density.Annihilation probability was suppressed strongly by the increasing generating threshold ofmeson which was included in annihilation channels, the lower probability means the longerlifetime of antibaryon. In the case of insu?cient energy space, e?ective mass of all meson mayoutrun the available energy, this situation leads to a total close of annihilation channels. Allmeson annihilation channels tends to be suppressed strongly near a critical nuclear densityρc = 2.685ρ0 and it may exist stably when the average density is larger than this criticalvalue. Namely, it forms a stable system which contains real nucleon and real antinucleonpossibly.Thirdly, the in?uence of antibaryon-meson coupling constants was studied. The varia-tion of interaction strength a?ects the lifetime of antinucleon signi?cantly. Particularly, thelifetime of antibaryon increases quickly in the weak interaction situation. The lifetime ofantibaryon isτ～10fm/c when the interaction strength of antibaryon-meson is as weak asone tenth of baryon-meson interaction strengthξ～0.1.Finally, the annihilation con?nement in high density region of nuclear center was studiedin the aspect of antinucleon distribution. Because the total increase of all meson generatingthreshold in the center of nuclear, the lifetime becomes signi?cantly long. The contradis-tinctive calculation with three di?erent parameterizations show the lifetime of antibaryonembedded in 16O + pˉis at leastτ> 6fm/c(NLZ2), or even exist stably(TM1). The relatedphenomena should be experimentally observed near and beyond the critical nuclear densityunder the condition of no Dirac sea e?ect was pointed out based on our theoretical results.Therefore, we suggest the antinucleon localized in 16O + pˉcan exist stably.