Are quarks as sub-atomic as it gets? necessarily?

[thetexan]

is there anything that says there cant be anything smaller than a quark? Can a quark be divided into sub-quark particles...in theory

[tom.stoer]

Yes, one could think about a substructure, but
1) there are no experimental indications
2) something would have to be rather strange, b/c usually you get something like E ~ 1/L where E is the energy of the bound state and L is the typical length scale; b/c L is extremely small, energy E and Mass m = E ~ 1/L should be large; in reality quarks are nearly massless, so there would have to be some additional mechanism ruling out large quark masses (it cannot be spontaneous symmetry breaking + Goldstone mechanism b/c this always creates massless bosons whereas quarks are spin 1/2 fermions)

[Drakkith]

If you look at the history of scattering experiments, there has continually been a hint that there are smaller particles. Alpha particle scattering off a nucleus led us to discover that the nucleus is actually a very very tiny portion of the atom yet contains over 99% of it's mass. Electron scattering off of protons led us to discover that there was an even smaller particle, the quark. So far, there has not been any more hints to further substructure as far as I know. But who knows, we are always smashing things into each other at higher and higher energy levels! Maybe we'll get a surprise!

[Meir Achuz]

There are many theory papers on substructure for quarks. I don't believe them, but search on preons in arxiv.org or google and stand back.

[VreemdeGozer]

I actually believe that the Rishon model is quite an interesting theory. It's based on the preon model, but has some differences which make it a lot more plausible.


http://www.weizmann.ac.il/home/harari/files/Nuclear_PhysicsB_Vol204.pdf (1981 paper)
http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-2310.pdf (1979 paper)