Mysterious X particle spotted in quark–gluon plasma at CERN – Physics World

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 and if confirmed, it could help researchers understand the structure of the exotic particle. 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. The exotic X particle – formally known as X(3872) because of it 3872 MeV mass – was first spotted by the Belle experiment in Japan. It has subsequently been studied by other experiments at electron–positron colliders and hadron colliders, but its nature is not fully understood.