Dong Xiang-Kun, Baru Vadim, Guo Feng-Kun, Hanhart Christoph, Nefediev Alexey
CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Zhong Guan Cun East Street 55, Beijing 100190, China.
School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
Phys Rev Lett. 2021 Apr 2;126(13):132001. doi: 10.1103/PhysRevLett.126.132001.
Recently, the LHCb Collaboration reported pronounced structures in the invariant mass spectrum of J/ψ pairs produced in proton-proton collisions at the Large Hadron Collider. In this Letter, we argue that the data can be very well described within two variants of a coupled-channel approach employing T matrices consistent with unitarity: (i) with just two channels, J/ψJ/ψ and ψ(2S)J/ψ, as long as energy-dependent interactions in these channels are allowed, or (ii) with three channels J/ψJ/ψ, ψ(2S)J/ψ, and ψ(3770)J/ψ with just constant contact interactions. Both formulations hint at the existence of a near-threshold state in the J/ψJ/ψ system with the quantum numbers J^{PC}=0^{++} or 2^{++}, which we refer to as X(6200). We suggest experimental tests to check the existence of this state and discuss what additional channels need to be studied experimentally to allow for distinctive tests between the two mechanisms proposed. If the molecular nature of X(6200), as hinted by the three-channel approach, is confirmed, many other double-quarkonium states should exist driven by the same binding mechanism. In particular, there should be an η_{c}η_{c} molecule with a similar binding energy.
最近，大型强子对撞机底夸克实验合作组报告了在大型强子对撞机质子 - 质子碰撞中产生的J/ψ对的不变质量谱中存在明显的结构。在本信函中，我们认为，在采用与幺正性一致的T矩阵的耦合通道方法的两个变体中，数据能够得到很好的描述：（i）仅使用两个通道，即J/ψJ/ψ和ψ(2S)J/ψ，只要允许这些通道中存在能量依赖的相互作用；或者（ii）使用三个通道J/ψJ/ψ、ψ(2S)J/ψ和ψ(3770)J/ψ，且仅具有常数接触相互作用。两种表述都暗示在J/ψJ/ψ系统中存在一个量子数为J^{PC}=0^{++}或2^{++}的近阈值态，我们将其称为X(6200)。我们建议进行实验测试以检验该态的存在，并讨论需要通过实验研究哪些额外的通道，以便对所提出的两种机制进行区分测试。如果如三通道方法所暗示的，X(6200)的分子性质得到证实，那么由相同束缚机制驱动的许多其他双夸克偶素态应该存在。特别是，应该存在一个具有相似结合能的η_{c}η_{c}分子。
