Nature of $X(6900)$ and its production mechanism at LHCb

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-$J\mathrm{/}\psi$ 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 $J\mathrm{/}\psi$-$J\mathrm{/}\psi$, $J\mathrm{/}\psi$-$\psi (2S)$ scatterings. A pole structure near the di-$J\mathrm{/}\psi$ threshold is also found. Meanwhile, we predict that $X(6900)$ can produce significant threshold enhancement in the $J\mathrm{/}\psi$-$\psi (2S)$ energy spectrum which can be searched for at LHCb.