Magnetic Monopoles and Free Quarks
A bar magnet is a magnetic dipole with a north pole and a south pole at its opposite ends. Can you cut the magnet to create isolated magnetic monopoles? Nobody has been able to do this yet: each part of the cut magnet develops new north and south poles, regenerating a new dipole. (However, some speculative extensions of the standard model do propose the existence of magnetic monopoles.) Moving the "separate monopoles or quarks" slider on the magnet graphic shows what happens when you pull a magnet apart.[more]
Free quarks, the building blocks of hadrons, have a somewhat analogous behavior. The charges responding to the strong interaction come in three "colors", conventionally designated as red, green, and blue. There also exist the corresponding "anticolors": anti-red, anti-green, and anti-blue. Carrying further the analogy with chromatic colors, these are sometimes called cyan, magenta, and yellow, respectively. (Compare magnetic and electric charges, in which just one "color" and one "anticolor" suffice.) Only color-neutral hadrons have been found in nature, consisting of color-anticolor pairs in mesons or red-green-blue triplets in baryons. The quarks are bound by gluons, shown as helices, and are continually interchanging colors in their dynamical interactions.
Each colored quark has six possible "flavors", not shown in this Demonstration. The most common quark flavors are up () and down (). Of higher energies are the strange (), charm (), bottom (), and top () quarks.
If, usually in a scattering process, one attempts to remove a quark from a hadron, the quark bond will stretch until enough energy is available to create a new quark-antiquark pair; the new antiquark cancels the color of the departing quark, while the new quark reconstitutes the original hadron. This is shown in the meson and baryon graphics.[less]