哈密顿有效场论对核子激发态研究的改进方案

The study of nucleon excited states is closely related to the property of nuclear force and plays an important role in revealing the strong interaction between basic particles. We propose to systematically study the masses, widths, related scattering, and other information of nucleon excited states, and thus obtain their properties such as the structure and components. Lattice QCD (LQCD) starts from the first principle in the standard model of particle physics and provides the new reliable information. Hamiltonian effective field theory (HEFT) analyzes both the new data from LQCD and the traditional data from the scattering experiment at the same time, and it can help us understand the nucleon excited states deeply and check the reliability of some phenomenological models. There are some successful but preliminary studies with HEFT, and systematical improvement to HEFT will definitely make us gain more delicate and physical picture of nucleon excited states. In detail, we propose to mainly consider the interfering effect of few excited states, description of two-to-two particle interaction in dynamical mechanism rather than with phenomenological model, higher-order corrections, and so on. We also plan to extend HEFT in order to analyze the quark distribution function provided by LQCD. The inclusion of these new considerations will push forward the previous studies with HEFT and make clearer conclusions. Improved HEFT can be easily extended as a powerful tool for analyzing other hadrons, and help to develop the hadron physics.

核子激发态的研究与核力的性质紧密相关，对揭示基本粒子间的强相互作用有重大意义。本申请项目旨在系统地研究核子激发态的质量、宽度、相关散射等信息，从而进一步理解以及明确这些态的结构成分等性质。格点量子色动力学从粒子物理标准模型第一性原理出发，提供了可靠的新信息。哈密顿有效场论利用这些新数据，同时结合传统的散射实验数据，可以给出对核子激发态的新理解，检验某些经验模型的合理程度。哈密顿有效场论已有一些初步的成功研究，系统的细化及扩展该理论势必会巩固和加深我们对核子激发态的认识。具体地，本项目计划在该理论中重点考虑多个核子激发态的干涉效应，两粒子相互作用的动力学机制描述而非模型描述，以及高阶修正等；也计划拓展该理论用来分析格点量子色动力学产生的夸克分布函数。预计这些新因素的加入能弥补之前研究的不足，得出更加明确的结论。改进的哈密顿有效场论亦可推广做为研究其它强子的有效工具，推动强子物理的进展。

强子相互作用、结构、质量谱等是粒子物理中彼此联系且十分重要的问题。哈密顿有效场论结合散射实验数据与格点量子色动力学在有限体积的结果，在处理强子相互作用以及核子激发态的结构与质量谱等问题上取得了很大的成功。在本项目的资助下，我们发展了哈密顿有效场论，用其研究K型氢原子与氘原子，发现由于近阈共振态的存在，反冲效应对K型氘原子基态的寿命起重要作用；我们用有效场论处理核子激发态的电磁跃迁与强子相互作用，结果显示圈图贡献对于强子的电磁性质及强相互作用有一定的修正；我们研究了含隐粲夸克对核子激发态及其他奇特强子态的质量，发现不同模型下强子相互作用的差别对强子质量谱影响很大，同时注意到有一些奇特强子态质量在不同的框架下变化不大。