A team have confirmed the existence of a four-quark particle, named Z(4430). The finding, together with other exotic particles, challenges the idea that quarks only combine in pairs (mesons) or triplets.

Z(4430) was first spotted in 2008 at the Belle detector in Japan, but another detector in California failed to see it, casting doubt on the initial observations. A team working on the LHCb experiment at CERN, Europe's particle physics laboratory near Geneva in Switzerland, analysed about a billion high-energy proton–proton collisions. The scientists noticed that in about 4,000 cases there was a highly significant Z(4430) signal — about 14 standard deviations above background levels.

The authors determined that the particle is composed of four quarks because of its observed decay patterns, and is not an artefact of interactions between ordinary two-quark mesons.

Phys. Rev. Lett. 112, 222002 (2014)