New particle may be made of four quarks

A newly discovered particle may have an exotic composition. The a₁(1420) particle, reported January 23 online at arXiv.org, could be made up of four quarks — the fundamental constituents of protons, neutrons and many other particles — rather than two or three like the vast majority of quark-based particles of matter.

Physicists found evidence for a₁(1420) in a cascade of subatomic debris using the COMPASS detector at CERN, the European physics lab located outside Geneva. The negatively charged particle has a mass about 1.5 times that of a proton. The unusual way a₁(1420) decays, the researchers say, may indicate that the particle is composed of four quarks, much like a few other recently discovered particles.