Physics (AS & A Level) · May / June 2016 · Paper 13 · Question 40

The magnitude of the charge on the proton may be regarded as +1 unit. On this basis, the charges on the up (u) quark, down (d) quark and their antiquarks ($\bar{u}$ and $\bar{d}$) are not whole units. Which row in the table shows the correct values for the charges on the u, d, $\bar{u}$ and $\bar{d}$ quarks?

1. Au: +2/3, d: −1/3, ū: +2/3, d̄: −1/3
2. Bu: −2/3, d: +1/3, ū: +2/3, d̄: −1/3
3. Cu: +2/3, d: −1/3, ū: −2/3, d̄: +1/3
4. Du: −2/3, d: +1/3, ū: −2/3, d̄: +1/3

As printed in the paper