A mysterious “X” particle comprising four quarks and first seen in 2003, has been found in the quark-gluon plasma produced in heavy-ion collisions at the Large Hadron Collider (LHC).
The observation was made by physicists working on CERN’s Compact Muon Solenoid (CMS) experiment.
Further studies of the particle could help explain how familiar hadrons such as protons and neutrons formed from the quark-gluon plasma believed to have been present in the early universe.