[论文解读] A survey of heavy-antiheavy hadronic molecules

Xiang-Kun Dong, Feng-Kun Guo+1 more|arXiv (Cornell University)|Jan 4, 2021

Quantum Chromodynamics and Particle Interactions参考文献 4被引用 129

一句话总结

本文通过求解对壳Bethe-Salpeter方程，在矢量介子交换饱和的接触相互作用下，系统性预测了重-反重荷哈道分子态谱，聚焦于S波和P波的重介子与重重子，并发现了229个预测态，其中若干近阈结构能够拟合到该谱系。

ABSTRACT

Many efforts have been made to reveal the nature of the overabundant resonant structures observed by the worldwide experiments in the last two decades. Hadronic molecules attract special attention because many of these seemingly unconventional resonances are located close to the threshold of a pair of hadrons. To give an overall feature of the spectrum of hadronic molecules composed of a pair of heavy-antiheavy hadrons, namely, which pairs are possible to form molecular states, we take charmed hadrons for example to investigate the interaction between them and search for poles by solving the Bethe-Salpeter equation. We consider all possible combinations of hadron pairs of the $S$-wave singly-charmed mesons and baryons as well as the narrow $P$-wave charmed mesons. The interactions, which are assumed to be meson-exchange saturated, are described by constant contact terms which are resummed to generate poles. It turns out that if a system is attractive near threshold by the light meson exchange, there is a pole close to threshold corresponding to a bound state or a virtual state, depending on the strength of interaction and the cutoff. In total, 229 molecular states are predicted. The observed near-threshold structures with hidden-charm, like the famous $X(3872)$ and $P_c$ states, fit into the spectrum we obtain. We also highlight a $Λ_c\bar Λ_c$ bound state that has a pole consistent with the cross section of the $e^+e^- oΛ_c\bar Λ_c$ precisely measured by the BESIII Collaboration.

研究动机与目标

• 激发人们将近阈共振理解为由重-反重对组成的强子分子态。
• 提供覆盖S-波和P-波的重介子和重重子组合的统一分子态谱。
• 使用由共振饱和的接触相互作用势并求解Bethe-Salpeter方程以定位近阈极点。

提出的方法

• 构建在重夸自旋对称性和手征SU(3)不变的重-介子和重-重子拉格朗日量。
• 从由共振饱和的轻矢量交换估计相互作用势；保留一阶常数接触项。
• 求解在壳Bethe-Salpeter方程 T = V + VGT，以定位极点。
• 考虑HQFS，通过用有机态相互作用作为底态系统的代理，关联Charm和Bottom扇区。
• 聚焦近阈动力学，简化忽略耦合通道，以得到统一的首轮光谱。

实验结果

研究问题

• RQ1 在HQSS和手征约束下，哪些重-反重荷哈道对可以形成近阈分子态？
• RQ2 矢量介子交换饱和的接触相互作用如何在这些系统的Bethe-Salpeter方程中产生极点？
• RQ3 在所研究的重-介子和重-重子扇区中预测了多少个分子态，它们与观测到的近阈结构如何对齐？
• RQ4 该模型能否将X(3872)、P_c等已知态纳入预测谱？
• RQ5 是否存在与BESIII截面数据相一致的Λ_c Λ̄_c束缚态极点？

主要发现

• 在多种重-反重荷阈附近预测总计229个分子态。
• 如X(3872)和P_c态等隐秘魅力的近阈结构，符合所预测的谱。
• 分析强调一个Λ_c Λ̄_c束缚态极点，与BESIII关于e+e− → Λ_c Λ̄_c横截面测量相一致。
• 该方法展示了阈动态和极点结构如何与不变量质量分布中的线形相关。
• 一阶常数相互作用，在矢量介子交换的饱和与重排后，足以在近阈产生极点并给出有意义的线形。
• 该研究提供了一个统一框架，将若干著名的近阈态与更广泛的分子谱预测联系起来。