Quarks: six flavours

By the end of this lesson

By the end you can say what makes a particle fundamental, name all six quark flavours, and explain why a proton is not one.

Fundamental means "no pieces inside"

A fundamental particle has no internal structure: it is not made of anything smaller. An electron appears to be fundamental. A proton is not, because it is built from smaller particles called quarks.

You cannot see a single quark. Quarks are never found on their own: they are always bound together inside particles such as protons and neutrons. That is why they were proposed from the pattern in the data long before any experiment could hint at them.

Definition

Quark flavour

Quarks come in six types, called flavours. They are naturally arranged in three pairs, called generations:

generation	flavours	symbols
first	up and down	$\text{u}$ , $\text{d}$
second	charm and strange	$\text{c}$ , $\text{s}$
third	top and bottom	$\text{t}$ , $\text{b}$

The first generation is the lightest, and it is the one that makes up ordinary matter: protons and neutrons contain only up and down quarks. The other four flavours are produced in high-energy collisions and decay quickly.

Why ordinary matter uses only two of the six

Heavier versions of the same thing are unstable. A top quark decays almost immediately; only the lightest, most stable combination survives in bulk matter.

Think of it like the lightest elements being the common ones in the universe: stability decides what you find lying around. Up and down quarks happen to give stable protons and neutrons, so those are the quarks your body is made of.

Worked example: Example: counting the flavours

A question asks how many quark flavours exist and gives a list containing $\text{u}$ , $\text{d}$ , $\text{s}$ , $\text{c}$ , $\text{t}$ , $\text{b}$ and $\text{e}^-$ .

Have a go first?

Check 1 — names and counts

CalculateQuestion 1 · Recall

Multiple choiceQuestion 2 · Recall

Answer the 2 questions above to continue.