Exotic four-quark particle spotted at Large Hadron Collider

Rare tetraquark is one of dozens of non-elementary particles discovered by the accelerator, and could help to test theories about strong nuclear force. The Large Hadron Collider (LHC) is also a big hadron discoverer. The atom smasher near Geneva, Switzerland, is most famous for demonstrating the existence of the Higgs boson in 2012, a discovery that slotted into place the final keystone of the current classification of elementary particles. But the LHC has also netted dozens of the non-elementary particles called hadrons — those that, like protons and neutrons, are made of quarks.

https://www.nature.com