Omega baryon
Omega baryons (often called simply omega particles) are a family of subatomic hadrons which are represented by the symbol Ω and are either charge neutral or have a +2, +1 or −1 elementary charge. Additionally, they contain no up or down quarks. Omega baryons containing top quarks are also not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s, which is about a twentieth of the timescale necessary for the strong interactions required for hadronization, the process by which hadrons form from quarks and gluons.
The earliest observed omega baryon was the Ω−
, made of three strange quarks. It was first observed in 1964. The discovery was a great triumph in the study of quarks, since it was found only after its existence, mass, and decay products had been predicted in 1961 by the American physicist Susumu Okubo and independently Murray Gell-Mann in a less accurate formula. A charmed omega particle (Ω0
c) was discovered in 1985, in which a strange quark is replaced by a charm quark. The Ω−
decays only via the weak interaction and therefore has a relatively long lifetime. Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.
Since omega baryons do not have any up or down quarks, they all have isospin 0.
The naming convention of baryons has become such that those with no light (i.e. up or down) valence quarks are called omega baryons. By default, the quarks are strange quarks, but those with one or more the strange quarks replaced by charm or bottom quarks have a subscript c or b, respectively.