We show that the Pomeron exchanges play a unique role in vector charmonium scatterings. Such a mechanism can provide a natural explanation for the nontrivial structures in the di-$J/\psi$ spectrum observed by the LHCb Collaboration. The narrow structure $X(6900)$, as a dynamically generated resonance pole, can arise from the Pomeron exchanges and coupled-channel effects between the $J/\psi$-$J/\psi$, $J/\psi$-$\psi (2S)$ scatterings. A pole structure near the di-$J/\psi$ threshold is also found. Meanwhile, we predict that $X(6900)$ can produce significant threshold enhancement in the $J/\psi$-$\psi (2S)$ energy spectrum which can be searched for at LHCb.

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X(6900)的性质及其在LHCb上的产生机制

我们表明 Pomeron 交换在矢量 Charmonium 散射中发挥着独特的作用。这种机制可以为二元结构中的非平凡结构提供自然的解释。$J/\psi$LHCb 合作组织观察到的光谱。狭窄的结构$X(6900)$，作为动态产生的共振极，可以由波梅隆交换和耦合通道效应产生 $J/\psi$——$J/\psi$, $J/\psi$——$\psi (2秒)$散射。靠近 di- 的杆结构$J/\psi$阈值也找到了。同时，我们预测$X(6900)$ 可以产生显着的阈值增强 $J/\psi$——$\psi (2秒)$ 可以在 LHCb 上搜索的能谱。