The $ar{ ext{Σ}}^0$ baryon, composed of the quark combination uds, is produced through the strong interaction between a $ ext{π}^+$ meson and a neutron - AQA - A-Level Physics - Question 11 - 2018 - Paper 1

To determine the quark composition of the particle X produced in the interaction, we can analyze the reaction:

1. The initial particles involved are:

   • The $ext{π}^+$ meson, which has a quark composition of uar{d}.
   • The neutron ($n$), which consists of the quark combination $udd$.

2. The final products of the reaction are:

   • The $ext{Σ}^0$ baryon, which is composed of $uds$.
   • The particle X, whose quark composition we need to find.

3. We can apply the conservation of baryon number and charge:

   • The total charge and baryon number before and after the interaction must remain the same.

4. Before the interaction:

   • The charge of the system is the sum of the charges of the particles: $+1$ (from $ext{π}^+$) + $0$ (from neutron) = $+1$.

5. After the interaction:

   • The $ext{Σ}^0$ baryon has charge $0$, so particle X must have a charge of $+1$ to balance the initial charge at $+1$.

6. Analyzing the answer choices:

   • A) $us̄$ (charge $0$)
   • B) $ud$ (charge $+1$)
   • C) $ud̄$ (charge $0$)
   • D) $ud̄s$ (charge $+1$)

7. Given that particle X needs to balance the reaction charge, the only suitable options are B or D:

   • Choice B ($ud$) does provide the required charge of $+1$.
   • Choice D ($ud̄s$) does as well; however, it consists of three quarks and is not the simplest form.

8. Therefore, the simplest and most appropriate answer is:

Answer: B - $ud$