[BBC Science News] Physicists have discovered a new class of subatomic particle. There are hundreds of subatomic particles known and most are composites of simpler particles. They all fit into two categories — baryons and mesons. Baryons are made of three quarks and mesons are comprised of two quarks — a quark and an anti-quark.
More than 99.9% of the mass of everyday objects is contained within the nucleus of atoms. This means that most of our body mass comes from subatomic particles that are made up of quarks. [And since I’m not a physicist: what’s the other 0.1%?]
The new particle is the so-called pentaquark — five quarks in formation. Until now, physicists had only seen quarks packed into two- or three-quark combinations.