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Particle Questions that include Feynman Diagrams

Q7.

(a) The negative kaon, K–, has a strangeness of –1. Write down its quark composition.

su

(for any quark + antiquark combination OR for using an s quark in a two quark combination one mark was awarded - so have a go!)

(2 marks)

(b) The kaon, K– may decay into a muon and an antineutrino in the following way:

(i) Complete the following table using ticks and crosses as indicated in the first row.

 

 

K–

 

μ–

 

ν μ

charged particle

X

hadron

X

X

meson

X

X

baryon

X

X

X

lepton

X

 

One mark for each correct line - all ticks and crosses must be correct for a particular particle class to get the mark.

(ii) In the decay shown above, charge is conserved. Give another quantity that is conserved and a quantity that is not conserved in the decay of K–.

quantity conserved lepton number OR baryon number OR energy OR momentum

quantity not conserved strangeness

(6 marks)

(c) The Feynman diagram below represents the β+ decay process.

(i) What quantity changes continuously in moving from the bottom to the top of the diagram? Time

(ii) Name the particles represented by the letters A to D. (see diagram - they ask you to name them, not give the symbols for them - if in doubt give both!)

(iii) What type of interaction is responsible for β+ decay? Weak Interaction

(6 marks)

(Total 14 marks)