AQA AS Level Physics Paper 2, November 2021: Question 8

1 mark · Medium difficulty · Multiple Choice

Identify the possible decay products of a baryon with quark structure dss decaying via the weak interaction.

Practise this question

Question

Multiple-choice question 8 asking for the possible decay products of a baryon with quark structure dss that decays by the weak interaction, giving options A (Lambda-zero plus pi-minus), B (neutron plus pi-minus), C (Lambda-zero plus e-minus), and D (K-plus plus K-zero).
Question text

08 A particular baryon has a quark structure dss and decays by the weak interaction.

What are possible decay products of this baryon?

The quark structure of Λ0 is uds.

[1 mark]

A Λ0 + π−

B n + π−

C Λ0 + e−

D K+ + K0

Mark scheme

Show the mark scheme Mark scheme for question 8 showing the correct answer is A.

08 A Λ0 + π−

How to answer it

Weak Interaction Decay of a Strange Baryon

What this question tests

This question assesses your knowledge of particle physics, specifically quark structures of hadrons, conservation laws in particle interactions (charge, baryon number, strangeness), and characteristics of the weak interaction (where strangeness can change by 0 or ±1).

Question 08 — Multiple Choice

Analysis & Correct Answer

✅ Correct Answer: A (Λ⁰ + π⁻)

Option A is correct because it conserves baryon number, charge, and allows strangeness to change by 1 through the weak interaction.

💡 Key Knowledge

  • Baryon dss: This is a cascade particle (specifically the Ξ⁻ particle, having quark content dss).
  • Strangeness: Each strange quark (s) has a strangeness of S = -1. Therefore, dss has a total strangeness of S = -2 .
  • Weak Interaction Rule: Strangeness can change by ΔS = 0 or ±1 in a weak decay.

🧠 Exam Technique

  • Check conservation laws systematically: Charge ( Q ), Baryon Number ( B ), and Strangeness ( S ).
  • Use the given information: You are told the quark structure of Λ⁰ is uds (which has S = -1 ).
  • A pion ( π⁻ ) has quark/antiquark structure d u-bar and S = 0 .

❌ Common Errors

  • Assuming strangeness must be strictly conserved (forgetting that weak interactions can violate strangeness conservation by ΔS = ±1 ).
  • Failing to count the number of strange quarks correctly (dss contains two strange quarks, so S = -2 ).
Mark Allocation: [1 mark] awarded for selecting option A.

Topics

Physics · 3.2 Particles and radiation

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.