Four-Charm-Quark Matter from the CMS Collaboration as a Witness of the Development of High-Precision Hadron Spectroscopy

Recent CMS observations in the di-$J\mathrm{/}\psi$ invariant mass spectrum reveal new structures at 6638 MeV ($X(6600)$)) and 7134 MeV, and confirm the $X(6900)$ at 6847 MeV. These findings provide crucial insights into four-charm-quark matter. The CMS Collaboration’s result serves as a testament to the progress in exploring exotic hadronic matter.