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Date November 2012 Marks available 1 Reference code 12N.3.HL.TZ0.22
Level Higher level Paper Paper 3 Time zone Time zone 0
Command term State Question number 22 Adapted from N/A

Question

This question is about quarks.

State the name of a particle that is its own antiparticle.

[1]
a.

The meson K0 consists of a d quark and an anti s quark. The K0 decays into two pions as shown in the Feynman diagram.

(i) State a reason why the kaon K0 cannot be its own antiparticle.

(ii) Explain how it may be deduced that this decay is a weak interaction process.

(iii) State the name of the particle denoted by the dotted line in the diagram.

(iv) The mass of the particle in (b)(iii) is approximately 1.6×10–25kg. Determine the range of the weak interaction.

[6]
b.

Markscheme

photon / graviton / Z / Higgs;

a.

(i) K0 has a strangeness of +1, its antiparticle has strangeness –1 and so are different;
the antiparticle is s, \(\overline d \) and so is different;

(ii) strangeness is violated in this decay;
this can only happen with the weak interaction;

(iii) Z0 / Z;

(iv) \(R = \left( {\frac{h}{{4\pi mc}} = } \right)\frac{{6.6 \times {{10}^{ - 34}}}}{{4 \times \pi  \times 1.6 \times {{10}^{ - 25}} \times 3.0 \times {{10}^8}}}\);
R≈10−18m;
Award [2] for a bald correct answer.

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Core » Topic 7: Atomic, nuclear and particle physics » 7.3 – The structure of matter
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