正反重强子对构成的强子分子态能谱

A survey of heavy-antiheavy hadronic molecules

近二十年来,世界上众多高能物理实验发现了大量超出传统夸克模型的共振结构。为了理解这些性质奇特的共振结构,科学家们提出了很多方法和模型。其中,因为实验上发现的这些奇特态大多处在一对强子阈值附近,强子分子态的观点得到了很多关注。本文我们将以粲–反粲强子对为例来探究哪些系统可以形成分子态,进而给出粲–反粲强子分子态的能谱。我们考虑了所有由S波粲介子、粲重子以及窄的P波粲介子构成的粲–反粲强子对。我们假定它们之间的相互作用由介子交换主导,在最低阶近似下可简化为常数。通过求解常数相互作用的Bethe–Salpeter方程,我们可以找到振幅的极点进而确定该系统分子态的质量。最终我们发现,那些通过轻矢量介子交换在阈值附近产生吸引力的系统,会存在一个靠近阈值的极点。不同的系统,由于其相互作用强度不同,极点可能会处于能量复平面的第一黎曼面或者第二黎曼面,分别对应于束缚态或者虚态。我们总共发现了229个强子分子态。很多实验上发现的那些位于粲–反粲强子对阈值附近的共振结构可以很好地与我们的结果吻合。另外,我们需要强调所预言的一个ΛcˉΛc分子态,这个态可以很好地解释北京正负电子谱仪(BESIII)上测量的数据。

Many efforts have been made to reveal the nature of the overabundant resonant structures observed by the worldwide experiments in the last two decades.Haxdronic molecules attract special a>ttention 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 st reng th of interaction and the cutoff.In total,229 molecular st ates are predicted.The observed near-threshold structures with hidden-charm,like the famous X(3872)and Pc states,fit into the spectrum we obtain.We also highlight a ΛcˉΛc bound state that has a pole consistent with the cross section of the e^(+)e^(-)→ΛcˉΛc precisely measured by the BESIII Collaboration.