Eur. Phys. J. C (2025) 85: 636
https://doi.org/10.1140/epjc/s10052-025-14364-x

Letter

Fully-heavy hadronic molecules $B_c^{(\ast )+}B_c^{(\ast )-}$ bound by fully-heavy mesons

School of Physics, Southeast University, 210094, Nanjing, China

^a hxchen@seu.edu.cn

Received: 16 April 2025
Accepted: 21 May 2025
Published online: 10 June 2025

Abstract

A lot of exotic hadrons have been reported in the past twenty years, which bring us the renaissance of the hadron spectroscopy. Most of them can be understood as hadronic molecules, whose interactions are mainly due to the exchange of light mesons, and specifically, light vector mesons through the coupled-channel unitary approach within the local hidden-gauge formalism. It is still controversial whether the interaction arising from the exchange of heavy mesons is capable of forming hadronic molecules. We apply the coupled-channel unitary approach to study the fully-heavy $b\overline{b}c\overline{c}$ system, where the exchanged mesons can only be the fully-heavy vector mesons $J/\psi$, $B_c^{\ast }$, and $\mathrm{{\rm Y}}$. Especially, the $J/\psi$ meson is much lighter than the $B_c^{(\ast )}$ mesons, so the present study can be taken as a general investigation on the question whether a lower-mass fully-heavy meson is able to bind two higher-mass fully-heavy hadrons. Our results suggest the existence of the fully-heavy hadronic molecules $|B_c^{+}{B}_c^{-};J^{\mathit{PC}}=0^{++}⟩$, $|B_c^{\ast +}{B}_c^{-}-c.c.;J^{\mathit{PC}}=1^{+-}⟩$, and $|B_c^{\ast +}B_c^{\ast -};J^{\mathit{PC}}=2^{++}⟩$ as well as the possible existence of $|B_c^{\ast +}{B}_c^{-}+c.c.;J^{\mathit{PC}}=1^{++}⟩$. These states are potential to be observed in the $J/\psi \mathrm{{\rm Y}}$, ${\mu }^{+}{\mu }^{-}J/\psi$, and ${\mu }^{+}{\mu }^{-}\mathrm{{\rm Y}}$ channels in future ATLAS, CMS, and LHCb experiments.