Three of the world's biggest particle accelerators combined their data to confirm a new form of matter made of four quarks.
April 23, 2026
Original Paper
Enhanced evidence of X(7200) and improved measurements of X(6900) parameters from a combined LHCb-ATLAS-CMS analysis
arXiv · 2604.18061
The Takeaway
Most matter in the universe is made of quarks grouped in twos or threes, like protons and neutrons. Data from the LHCb, ATLAS, and CMS experiments now confirm the existence of a tetraquark made of four heavy charm quarks. This exotic particle challenges the simple models physicists use to describe the strong nuclear force. The evidence for this state is now so strong that it is statistically impossible for it to be a fluke. This discovery proves that the building blocks of the universe can stick together in much more complex ways than we imagined. It provides a new testing ground for the laws that hold the core of every atom together.
From the abstract
We report enhanced evidence for the $X(7200)$ state and significantly improved measurements of the $X(6900)$ resonance parameters through a combined analysis of the di-$J/\psi$ mass spectrum using published data from LHCb, ATLAS, and CMS. By performing simultaneous fits to all three experiments, we observe the $X(6900)$ with overwhelming significance ($>12\sigma$) and determine its mass and width with improved precision. For the $X(7200)$, we find consistent signals across multiple interference