Charge of the charm and bottom quarks

We have repeatedly remarked that the assmnption that the charm quark has electric charge 2/3 makes it the natural candidate to be the missing 

That the charm quark charge is 2/3 is also borne out by the size of the increase in the ratio R (see Fig. 14.1) on crossing the charm threshold (i.e. much bigger than would be the case for a Q = 1/3 quark). 

Because the b quark is part of an entirely new doublet, no natural assumption is possible in the sense that its partner (the top) is still missing. 

In contrast to the charm case, the bottom quark charge assignment Qh = —1/3 comes from the moderate increase of R above the b threshold. This assignment is confirmed by the charge of the B ub). 

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