新强子态谱学的唯象研究

In recent decade, the research of new hadron states is one of the leading edges as well as hot topics of the hadron physics in both experimental and theoretical sides. The observations of the new hadron states provide a good opportunity for searching of the highly excited hadron states predicted by the traditional quark model. However, these observations are also great challenges for the quark model. On the theoretical side, the study on the new hadron states not only reveals the inner structures of these new hadron states, but also enlarges our understanding of the QCD at low energy. In the present program, we will study on the spectrum of new hadron state from three different aspects, which are highly excited hadrons, deuteron-like molecular states and hadron-hadron resonances. We will adopt the modified relativistic quark model to study the hadron spectrum. By comparing the hadron spectrum and decay behavior with the observed new hadron states, we can further categorize the new hadron states as highly excited hadrons. For some near thresholds new hadron states, we will study the near thresholds hadron-hadron interaction with effective field theory. With complex scaling method, we evaluate the possibilities of bound states composed of near threshold hadron pair and resonances resulted from the near threshold hadron-hadron interaction. These investigations on the new hadron states play an important role in explaining the natures of the observed new hadron states. Based on the inner structures of the new hadron states, we can further predict their spectrum and decay behavior. These predictions can provide useful information for further experimental measurements in the BESIII, LHCb and forthcoming Belle II.

新强子态性质的研究是近十多年来强子物理实验和理论研究的前沿和热点之一。新强子态的发现为寻找传统夸克模型预言的强子高激发态提供了良好的机遇，同时也对传统夸克模型提出了新的挑战。对新强子态的理论研究能够揭示新强子态的内部结构，加深我们对低能QCD理论的理解和认识。本项目将从强子高激发态、类氘分子态和强子-强子共振态等方面对新强子态的谱学开展研究。利用修改的相对论夸克模型研究强子高激发态的谱学并与实验观测到的新强子态比较，进而确定其在强子谱中的位置。结合实验观测到的近阈新强子态，我们将利用有效场论的方法来研究阈值附近的强子-强子相互作用，利用复标度方法研究形成束缚态或者强子-强子共振态的可能性。这些研究对解释实验上观测到的新强子态的性质有重要意义，同时本项目的研究能够结合新强子态的内部结构计算其谱学和衰变行为，为BESIII、LHCb和Belle II上的相关实验提供一定的理论支持。

自从2003年Belle合作组发现X(3872)以来，实验上发现了越来越多的新强子态，这些新强子态对现有的夸克模型提出了挑战，同时为我们寻找传统强子的激发态和QCD奇特态提供了很好的机遇。本项目从主要从质量谱、衰变行为和产生行为等角度对新强子态的性质开展了一系列研究。我们利用有效拉氏量来描述强子之间的相互作用，并计算强子之间的相互作用势，通过求解Bethe-Salpeter方程来确定是否可以形成束缚态；我们还利用夸克模型直接计算四夸克态的质量谱，我们的计算发现某些四夸克态的质量低于相应的介子对的阈值，因此他们不能直接裂变为介子对，具有较长的寿命；我们在分子态的框架下对一些近阈的新强子态的衰变行为进行了研究，并与相关的实验观测比较来确定其为分子态的可能性，同时我们还预言了一些实验上未观测到的衰变行为；对于目前实验上已经观测到的新强子态，我们除了研究其质量和衰变行为外，我们还研究了其产生行为，并预言了新强子态的一些新的产生过程。本项目的这些研究一方面对目前实验观测提出了理论解释，另一方面预言一些新的现象，为实验上进一步观测新强子态提供理论支持。