All
elementary particles have a
baryon number. Baryons have a +1 value and antibaryons -1. Almost all other
particles have a baryon number of
zero except for
quarks and
antiquarks which have baryon numbers of 1/3 and -1/3, respectively. The baryon number for
quarks is derived from the fact that all baryons or
antibaryons are composed of exactly three
quarks or
antiquarks.
The baryon number is always conserved in particle interaction. This is a key concept in quantum physics because it governs the restrictions as to when and how many quarks get generated with each particle interaction.