Question

The quark content of the neutron is $\mathit{u}\mathit{d}\mathit{d}$. (a) What is the quark content of the antineutron? Explain your reasoning. (b) Is the neutron its own antiparticle? Why or why not? (c) The quark content of the $\mathit{\psi }$is $\mathit{c}\overline{\mathbf{c}}$. Is the $\mathit{\psi }$ its own antiparticle? Explain your reasoning.

Short answer

(a) The quark content of the antineutron is $\overline{\mathbf{u}\mathbf{d}\mathbf{d}}$.

(b) No, neutron does not have its own antiparticle.

(c) Yes, the particle $\psi$can be tis own antiparticle.

Step-by-step solution

(a) Determine the quark content of the antineutron 

A neutron is made up of quarks $udd$and for the antineutron, quarks in the composition $udd$are changed antiquarks $\overline{udd}$.

Thus, an antiparticle must contain antiquarks.

 (b) Determine if the neutron is its own particle

The baryon number of neutron $\left(B=+1\right)$is different from the baryon number of antineutron $\left(B=-1\right)$, therefore theneutron is not its own antiparticle.

(c) Determine if the particle ψ is its own particle

We know that the quark content of $\psi$is $c\overline{c}$, this means for the antiquark, the content is $\overline{c}c$, $\psi =c\overline{c}=\overline{c}c=\overline{\psi }$.

Therefore, the particle $\psi$can be its own antiparticle $\overline{\psi }$.