The journal Nature has just published the latest results from the CMS Collaboration at the LHC (CERN) on tetraquarks of the (c,c,c,c) type, sometimes referred to as “fully-charmed.” These states have a mass of around 7 GeV and decay into four muons. The first theoretical works predicting this particle date back to 1981 and were initiated by Jean-Marc Richard, Emeritus Researcher at IP2I. Three spin-2 states are clearly identified. This is the first time that the quantum numbers of these tetraquarks have been determined so convincingly. The IP2I CMS team did not participate in this analysis, but it played a very important role in the construction of the CMS detector together with IP2I engineers and technicians, and subsequently in data analysis and detector upgrades for the future HL-LHC. Many theorists are now studying multiquark states involving heavy quarks, and their models can be confronted with the results presented in this CMS publication.

See the Nature article:  : https://www.nature.com/articles/s41586-025-09711-7

The CMS press release: https://cms.cern/news/cms-gets-acquainted-family-all-charm-tetraquarks

And the article in Le Monde: https://www.lemonde.fr/sciences/article/2025/12/17/des-chercheurs-du-cern-devoilent-l-intimite-des-tetraquarks-des-particules-tres-fugaces_6658287_1650684.html