Particle Physics Questions


(a) Hadrons are a group of particles composed of quarks. Hadrons can either be baryons or mesons.

(i) What property defines a hadron?

Hadrons are particles that experience the strong (nuclear) force/interaction.

(ii) What is the quark structure of a baryon?

A Baryon is made up of three querks.

Do NOT talk of anti-quarks - three anti-quarks make up an anti-baryon. Do not speak of a limit to the flavour of quarks, there are a lot more baryons than the ones on your syllabua.

(iii) What is the quark structure of a meson?

A meson is made up of a quark and an anti-quark.

(3 marks)

(b) State one similarity and one difference between a particle and its antiparticle.

Similarity: the same (rest) mass or (rest) energy

Difference: opposite charge, opposite baryon number or opposite lepton number

(2 marks)

(c) Complete the table below which lists properties of the antiproton.

baryon number
quark structure
1.6 x 10-19

-1 for each mistake or omission

(2 marks)

(d) The is an example of a meson with strangeness –1.

It decays in the following way:

(i) State, with a reason, what interaction is responsible for this decay. (2 marks)

Weak interaction because strangeness is not conserved.

(ii) State two properties, other than energy and momentum, that are conserved in this decay.

  • charge
  • baryon number
  • (muon) lepton number

Any two

(2 marks)

(Total 11 marks)