7.3 The Structure of Matter

A young student of physics reads up about particles and anti-particles.

 In their physics lesson, they excitedly tell their teacher how they learned that a proton has an anti-particle called an anti-proton, and the neutron has an anti-particle called an anti-neutron.

 They go on to say that, since the neutron is neutrally charged, it is its own anti-particle.

Interactions between protons and neutrons can temporarily violate conservation laws.

One such interaction is shown.

The baryon decuplet is a vision tool used by particle physicists to classify groups of particles called baryons.

In the baryon decuplet, strangeness S is plotted on the horizontal axes and charge Q is plotted on the diagonal axe. Some information is missing.

(i)   State two particles that are their own antiparticle.

[2]

   (ii)         Explain why K⁰ is not its own antiparticle.

[1]

Heavier quarks can decay into lighter quarks by exchanging a virtual particle that meditates the type of interaction. This particle can then decay into a quark and its equivalent anti–quark.

Muons decay via the same interaction as the K⁰ meson into leptons. One such decay is