Strange particles and strangenessAQA A-Level Physics: Subtopic test

1. 1
   In a collision experiment a fast-moving proton collides with a stationary proton, and the reaction p + p → p + p + K⁺ + K⁻ is observed. The strangeness of K⁺ is +1.

   (a)

   What is the strangeness of K⁻?

   [1 mark]

   • A−1
   • B0
   • C+1
   • D+2

   (b)

   Which interaction is responsible for the production of the kaons in this reaction?

   [1 mark]

   • AGravity
   • BStrong
   • CWeak
   • DElectromagnetic

   (c)

   Explain why the K⁺ and K⁻ are produced together in this reaction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The neutral kaon K⁰ has strangeness +1 and decays into a π⁺ and a π⁻ with a mean lifetime of about 10⁻¹⁰ s. Reactions that produce kaons from collisions between hadrons typically take place in about 10⁻²³ s.

   (a)

   Which interaction is responsible for the decay of the neutral kaon into two pions?

   [1 mark]

   • AStrong
   • BElectromagnetic
   • CWeak
   • DGravitational

   (b)

   What is the change in strangeness in the decay K⁰ → π⁺ + π⁻?

   [1 mark]

   • A+1
   • B0
   • C+2
   • D−1

   (c)

   Suggest why kaons are described as strange particles, using the information given.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Physicists use conservation laws to decide which reactions can occur through the strong interaction. The strangeness of K⁺ and K⁰ is +1 and the strangeness of K⁻ is −1. Protons, neutrons and pions have strangeness 0.

   (a)

   Determine whether the reaction p + p → p + n + K⁺ can occur through the strong interaction.

   [3 marks]

   (b)

   The K⁻ is observed to decay into a π⁻ and a π⁰. Calculate the change in strangeness, state the interaction responsible and explain whether this change is allowed.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   At a particle accelerator, negative pions are fired at a liquid hydrogen target (protons) and the products are examined. The strangeness of K⁺ and K⁰ is +1 and the strangeness of K⁻ is −1. Protons, neutrons and pions have strangeness 0.

   (a)

   Explain what is meant by strange particles, how the quantum number strangeness describes their behaviour and how conservation of strangeness differs between the strong and weak interactions.

   [6 marks]

   (b)

   Evaluate whether each of the reactions π⁻ + p → K⁺ + K⁻ + n and π⁻ + p → K⁰ + n could take place through the strong interaction, and state what your conclusions show about the production of strange particles.

   [6 marks]

   Total for question 4: 12 marks

End of questions