- A quark with a charge of - 1/3 and a mass about 10,000 times that of the electron. Also known as beauty quark. See dining table at subatomic particle.
- A quark having a fractional electric cost of -1/3 and a mass about 4,100 to 4,400 MeV. Symbolization: b
- a quark with a charge of -1/3 and a mass about 10,000 times that of an electron