SU(4), …

9.4 $S U (4)$ , …

Once we have three ﬂavours of quarks, we can ask the question whether more ﬂavours exists. At the moment we know of three generations of quarks, corresponding to three generations (pairs). These give rise to SU(4), SU(5), SU(6) ﬂavour symmetries. Since the quarks get heavier and heavier, the symmetries get more-and-more broken as we add ﬂavours.

Table 9.2: The properties of the three quarks.



Quark	label	spin	$Q ∕ e$	mass (GEV/c $^{2}$ )

Down	$d$	$\frac{1}{2}$	$- \frac{1}{3}$	0.35
Up	$u$	$\frac{1}{2}$	$+ \frac{2}{3}$	0.35
Strange	$s$	$\frac{1}{2}$	$- \frac{1}{3}$	0.5
Charm	$c$	$\frac{1}{2}$	$+ \frac{2}{3}$	1.5
Bottom	$b$	$\frac{1}{2}$	$- \frac{1}{3}$	4.5
Top	$t$	$\frac{1}{2}$	$+ \frac{2}{3}$	93

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9.4 SU(4), …

9.4 $S U (4)$ , …