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

Abstract

Very recently, the CMS Collaboration reported a peaking phenomenon existing in the di-$J/\ensuremath{\psi}$ 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 $J/\ensuremath{\psi}$-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 $J/\ensuremath{\psi}J/\ensuremath{\psi}$. The present work provides a special viewpoint to decode these observed fully charm structures in the $J/\ensuremath{\psi}$-pair invariant mass spectrum.