【作者】 杨威；

【导师】 孙保元；

【作者基本信息】 兰州大学 ， 物理学·粒子物理与原子核物理， 2024， 硕士

【摘要】 由于不受核子泡利不相容原理的限制,超子可以深入到原子核内部成为理解其结构的敏感探针。此外,超核研究也为人们理解不同种类的重子-重子相互作用提供重要途径。目前,人们广泛研究的超核中所包含的超子一般携带奇异夸克。除了含有奇异夸克的超子,实验上还发现了携带粲夸克的Λ_c~+超子。由于其性质和Λ超子类似,Λ_c~+超子也可能和原子核结合形成另一类超核,即含粲超核。对于含粲超核的研究不仅为人们理解原子核结构提供了新的视角,还丰富了人们对于不同种类重子之间相互作用的认识。由于含粲超子寿命极短,因此实验上没有明确的含粲超核信号。因此,人们主要在理论上对含粲超核的性质开展研究。对于超核结构的研究首先需要确定含粲超子-核子之间的相互作用。目前为止,人们采用一些理论模型开展了Λ_cN相互作用的研究。由于理论模型的差异,得到的Λ_cN相互作用也不尽相同,这对含粲超核性质的描述将产生不确定性。因此,选取比较可靠的Λ_cN相互作用对于含粲超核的描述非常重要。在缺乏实验信息的情况下,近期根据格点QCD模拟和手征有效场论得到的结果为人们研究超核性质提供了重要的参考。本论文基于原子核的相对论密度泛函理论,包括相对论平均场(RMF)及相对论Hartree-Fock(RHF)理论,将其拓展包含Λ_c~+超子自由度并用以研究超核结构性质。该理论中的核子-核子(NN),超子-核子(Λ_cN)有效相互作用采用密度依赖和非线性两种形式。结合所选取的核多体方法和微观第一性原理得到的核物质中Λ_c~+超子势,本论文对Λ_c~+超核的存在性和质量极限、影响超核稳定性的因素、Λ_c~+超子对原子核结构的影响等开展了理论研究。对于密度依赖的相对论平均场,发现由于耦合强度的密度依赖性引起的重排项贡献,对质量数较小的含粲超核稳定性具有重要影响。另外,重排项可以引起不同有效相互作用在超子势场描述中的差异。进一步,本论文采用非线性平均场对含粲超核结构开展理论探索。发现在核物质中Λ_c~+超子势描述方面,两种模型给出了不同的模型依赖性。在含粲超核存在范围预测上,当两种模型给出相似的核物质超子势行为时,非线性和密度依赖有效相互作用都给出了一致的范围。而后,基于非线性有效相互作用本论文又研究了势场约束的不确定性对超核性质描述的影响。发现饱和密度处势场的不确定性将对超子单粒子能级及其他性质造成一定影响。最后,本论文还初步讨论了相对论Hartree-Fock模型对于含粲超子势的描述。论文研究表明,核介质效应的不同处理方式对含粲超核结构描述将产生显著影响,并且在有限密度下对于Λ_cN相互作用的约束至关重要。相关研究结论在一定程度上加深了人们对于有限密度下Λ_cN相互作用的理解。更多还原

【Abstract】 Hyperons in hypernuclei are not subject to the nucleon’s Pauli exclusion principle,allowing them to penetrate deep into the interior of atomic nuclei,making them a sensitive probe for understanding the structure and other properties of atomic nuclei.Currently,the hyperon widely studied in hypernuclei generally carries strange quarks.In addition to hyperons with strangeness,baryons carrying charmed quarks,such as theΛ_c~+hyperon,have also been discovered in theories and experiments.The composition of charmed hyperons is very similar to that ofΛhyperons,with the only difference being the replacement of the quark with strangeness in theΛhyperon with a charmed quark.Due to their similar composition,Λ_c~+hyperons may also combine with atomic nuclei to form another type of hypernuclei,namely charmed hypernuclei.The study of charmed hypernuclei not only provides a new perspective for our understanding of the structure of atomic nuclei but also enriches our knowledge of the interactions between different types of baryons.Due to the short lifetime of charmed hyperons and the high experimental con-ditions required for the formation of hypernuclei with atomic nuclei,the current experimental data related to charmed hypernuclei is very limited.Therefore,people usually use different theoretical models to study the properties of charmed hypernu-clei.The study of hypernuclear structure requires the interaction between charmed hyperons and nucleons.So far,people have carried out related studies using differ-ent theoretical models.Due to the differences in the theoretical models used,the obtainedΛ_cN interaction is different.DifferentΛ_cN interactions will also introduce some uncertainty in the description of the properties of charmed hypernuclei.There-fore,selecting a more reliableΛ_cN interaction is very important for the description of charmed hypernuclei.Recently,the interaction ofΛ_c~+hyperons in nuclear matter calculated from first principles has provided a good reference for us to study the properties of hypernuclei.This paper is based on the relativistic density functional theory,including rela-tivistic mean field(RMF)and relativistic Hartree-Fock(RHF)theories,and extends them to hypernuclei containing charmed baryons,deriving the theoretical formulas for charmed hypernuclei.The effective interactions between nucleon-nucleon(NN)and hyperon-nucleon(Λ_cN)in the relevant theories adopt both density-dependent and nonlinear forms.By combining the selected nuclear many-body methods and the potential fields ofΛ_c~+hyperon in nuclear matter obtained from chiral effective field theory,research has been conducted on the existence and mass limits ofΛ_c~+hypernuclei,factors affecting the stability of hypernuclei,and the impact of hyperon on the structure of atomic nuclei.For the density-dependent relativistic mean field,it is found that the rearrangement terms contribution caused by the density depen-dence of the coupling constant plays an important role in the stability of charmed hypernuclei with smaller mass number.Additionally,by studying the contributions of various parts of the hyperon potential field,it is also found that the difference in the hyperon potential fields obtained from different effective interactions mainly stem from the difference in the rearrangement terms contribution.This indicates that different treatments of medium effects will have a significant impact on the description of the stability and single-particle properties of charmed hypernuclei.Furthermore,this paper conducts research on the structure of charmed hyper-nuclei using non-linear relativistic mean-field theory.It is found that in describ-ing the hyperon potential in nuclear matter,the non-linear and density-dependent models provide different density dependencies.To better satisfy the constraints of hyperon potential in nuclear matter,symmetry breaking effects were also considered by adjusting the effective interactions between hyperon and nucleons.Based on this consideration,when predicting the existence range ofΛ_c~+hypernuclei with similar hyperon potentials in nuclear matter,both non-linear and density-dependent models give consistent ranges.Subsequently,based on the non-linear interaction,the im-pact of the uncertainty of the constrained potential on the description of hypernuclei properties was studied.It is found that the uncertainty of the potential at satura-tion density has a significant impact on the single-particle energy levels of hyperons and other properties.Through this work,It is shown that different treatments of nuclear medium effects could lead to discrepancies in the theoretical description of hypernuclear structures,even when different models yield similar hyperon potentials within nuclear matter,indicating that constraints on theΛ_cN interaction at finite densities are crucial for the study ofΛ_c~+hypernuclear structures.更多还原