PX156 - F4 - quarks

properties

• make up all matter

• feel all forces

• carry 3 charges: $Q,T_W,$ colour

• 3 types of colour charges:

  • red ($r$)
  • green ($g$)
  • blue ($b$)

• come with anti-particles: $\overline{u},\overline{d},\overline{c},\overline{s},\overline{t},\overline{b}$

  • charges have opposite signs:
  • colours: $\overline{r},\overline{g},\overline{b}$

• eg:

  • $u:Q=+\frac{2}{3}e,T_W=+1.2,r$
  • $\overline{u}:Q=-\frac{2}{3}e,T_W=-1.2,\overline{r}$

• $Q,T_W$ and colour are all conserved quantities

flavour number

• similar to lepton number

• can use $\pm 1$ for $u,d$
• the numbers are assigned to quarks of the same flavour
• for other flavours, the number will be zero

conservation of flavour

• flavour is conserved for electromagnetic and strong interactions
• it is violated by the weak interaction
• flavour non-conservation does not automatically imply that an interaction cannot happen