Improved understanding of the peaking phenomenon existing in the new di-$J/\psi$ invariant mass spectrum from the CMS Collaboration

Abstract

Very recently, the CMS Collaboration reported a peaking phenomenon existing in the di-$J/\psi$ invariant mass spectrum from $pp$ collision, by which the $X(6900)$ structure announced by the LHCb Collaboration was confirmed, but also more enhancement structures were discovered. Facing such a novel phenomenon, in this work we indicate that these new features reflected from the CMS measurement provide a good implication for a dynamical mechanism which reproduces the novel peaking phenomenon in the reported $J/\psi$-pair mass spectrum well. This mechanism is due to special reactions, where different charmonium pairs directly produced by $pp$ collision may transit into the final state of $J/\psi J/\psi$. The present work provides a special viewpoint to decode these observed fully charm structures in the $J/\psi$-pair invariant mass spectrum.