Physicists at accelerators in Japan and the United States have detected a subatomic particle that may be unlike any seen before.
Some evidence suggests that the particle contains two pairs of more fundamental particles–quarks and antiquarks–bound together. If that's verified, then the new find would be the first four-quark particle known.
Until recently, quarks and antiquarks were observed only in groups of twos or threes. However, twice this year, researchers have reported possible five-quark particles (SN: 10/18/03, p. 245: New Quarktet: Subatomic oddity hints at pentaparticle family).
The discovery of yet other combinations of quarks and antiquarks could illuminate the force that binds quarks and antiquarks together. Physicists call this the strong force.