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

TL;DR

This paper proposes that Pomeron exchanges and coupled-channel effects explain the observed $X(6900)$ resonance in di-$J/psi$ spectra at LHCb, predicting a threshold enhancement in $J/psi$-$psi(2S)$ channels.

Contribution

It introduces a novel mechanism involving Pomeron exchanges and coupled-channel effects to explain the $X(6900)$ resonance as a dynamically generated state.

Findings

$X(6900)$ can be explained as a resonance pole from Pomeron exchanges.

A near-threshold pole structure is identified in the di-$J/psi$ spectrum.

Predicted threshold enhancement in $J/psi$-$psi(2S)$ spectrum at LHCb.

Abstract

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.