[matthewh (OP)]

Today we had Susan ask us:

Normally the answer for “what are electrons, protons and neutrons made of” is “quarks”. But if that is the case, then what are quarks made of?

Let us know what you think!

[evan_au]

Short answer: At this point, we really don't know.

To explore tinier things (like "what is inside a quark?"), you need higher energies.

The largest energies we can achieve at present are at the Large Hadron Collider, up to 14 TeV.
- It is able to explore "jets" that occur when quarks are scattered during proton collisions
- It is able to explore the "quark gluon plasma" that occurs when heavy ions collide
- But it does not have enough energy to peer inside a single quark
- In fact, some theories suggest that you can never examine just a single quark - they always seem to hang around in groups with integer electrical charge

One of the challenges with colliding protons is that each proton has 3 quarks, so it is actually a collision of 6 quarks, and the results are very "messy".

Some researchers suggest that to produce "cleaner" collisions at higher energies, it would be better to use electrons - this contributed to the initial discovery of quarks.
See: https://en.wikipedia.org/wiki/Quark#History

Some researchers suggest that hypothetical "preons" might make up the more familiar particles, but there is no experimental evidence for them at this time.
See: https://en.wikipedia.org/wiki/Preon

[jeffreyH]

Mesons are made up from two quarks. One quark and one anti-quark. They are very unstable and decay into electrons and neutrinos. The proton appears to be the only stable composite particle made of quarks. Free neutrons also decay after around 15 minutes.

If the proton wasn't stable then we wouldn't be here discussing physics.

Find out about mesons here. https://en.m.wikipedia.org/wiki/Meson

Find out about composite particles here. https://en.m.wikipedia.org/wiki/List_of_particles#Composite_particles

[jeffreyH]

I have a question here. What are the decay products of two colliding antiprotons?

[evan_au]

What are the decay products of two colliding antiprotons?

Statistically speaking, they are the same as the products of two colliding protons - only they are all antiparticles.
- Bearing in mind that some particles (eg photons) are their own antiparticle.

There are some very slight deviations for decays involving the Weak nuclear force
- Physicists are on the lookout for these asymmetries, as they are trying to understand why the universe today is almost totally matter, rather than antimatter
- These small asymmetries might account for part of it, but are probably not the whole story

See: https://en.wikipedia.org/wiki/Baryon_asymmetry

[alancalverd]

Big fleas have little fleas
Upon their backs to bite 'em
And little fleas have lesser fleas
Et sic ad infinitum

[evan_au]

what are quarks made of?

One theory that tries to explain all the subatomic particles that we see is string theory.

At present there is no experimental evidence for it, and the theory has great difficulty representing any of the familiar subatomic particles, like electrons, photons or quarks.

It's main claim to fame (so far) is that it is able to reproduce the graviton and general relativity.
See: https://en.wikipedia.org/wiki/String_theory

[Fussball]

A quark is a size zero particle. It is not made of anything.

[evan_au]

Maybe Stting Theory can represent photons?
...or maybe they have just defined some constraints on string theory if it is to ever successfully describe a photon...
https://en.wikipedia.org/wiki/Relationship_between_string_theory_and_quantum_field_theory