Baryon Number - Baryon Number Vs. Quark Number

Baryon Number Vs. Quark Number

Quarks do not only carry electric charge, but also additional charges such as color charge and weak isospin. Because of a phenomenon known as color confinement, a hadron cannot have a net color charge; that is, the total color charge of a particle has to be zero ("white"). A quark can have one of three "colors", dubbed "red", "green", and "blue".

For normal hadrons, a white color can thus be achieved in one of three ways:

• A quark of one color with an antiquark of the corresponding anticolor, giving a meson with baryon number 0,
• Three quarks of different colors, giving a baryon with baryon number +1,
• Three antiquarks into an antibaryon with baryon number −1.

The baryon number was defined long before the quark model was established, so rather than changing the definitions, particle physicists simply gave quarks one third the baryon number. Nowadays it might be more accurate to speak of the conservation of quark number.

In theory, exotic hadrons can be formed by adding pairs of quark and antiquark, provided that each pair has a matching color/anticolor. For example, a pentaquark (four quarks, one antiquark) could have the individual quark colors: red, green, blue, blue, and antiblue.