Resonant Charmonium Pair Production: a Comprehensive Review of Theoretical and Experimental Advances

The narrow resonant-like structures were identified in the invariant mass spectra of di- $$J/\psi$$ and $$J/\psi{-}\psi(2S)$$ by three LHC collaborations. These findings point to the possible existence of fully-heavy tetraquarks with a $$c\bar{c}c\bar{c}$$ configuration. These new exotic resonances require detailed theoretical and experimental investigation. In this review, the latest experimental results and several theoretical approaches towards physics of new states are presented.