described below. The name ‘quark’ is now used to describe six different ‘flavours’, or types, of particle that make up bigger subatomic particles.
Time 2000
STS
The quark model was proposed by Murray Gell-Mann and George Zweig in 1964 but it was Gell-Mann who won the argument of choosing the name for the fundamental constituents. If Zweig had got his way, we would be calling them ‘aces’ rather than ‘quarks’!
10–10 metres
FIG. 32.16 Overview of diminishing dimensions as we travel from the atomic diameter inwards
There are six quarks and six accompanying antiquarks. Table 32.3 shows the symbol and charge of each type.
STS
The names up/down, top/ bottom and strange/charm were arbitrarily given in pairs to each set of quarks. Top and bottom were very nearly called ‘truth’ and ‘beauty’!
up
Quark Symbol Charge Antiquark Symbol Charge + 2
u
down d top
t
bottom b strange s charm c
__ 3
− 1 + 2 − 1 − 1 + 2
__ 3
__ 3
__ 3
__ 3
__ 3
anti-up
anti-down anti-top
anti-bottom anti-strange anti-charm
__ u
__ d
_ t
__ b
_ s
__ c
TABLE 32.3 Symbol and charge of each type of quark and antiquark
Looking at the quark structure, you will notice that they have fractional charges of either + 2
__ 3 or – 1
__ 3 . In order for particles to be stable, they require whole integer
charges. It is for this reason that all particles made from quarks or antiquarks are joined in such a way as to have integer net charges. For example, a proton is made
up of two ‘up’ quarks and one ‘down’ quark. This adds up to 376 FUSION
