Q9.

(a) Baryons, mesons and leptons are affected by particle interactions.

Write an account of these interactions.

Your account should:

include the names of the interactions

identify the groups of particles that are affected by the interaction

identify the exchange particles involved in the interaction

give examples of two of the interactions you mention.

The quality of your written communication will be assessed in your answer.

For this type of question your writing should be legible and the spelling, punctuation and grammar should be sufficiently accurate for the meaning to be clear.

Your answer will be assessed holistically.

It will be assigned to one of three levels according to the following criteria:

High Level (Good to excellent): 5 or 6 marks

The information conveyed by the answer must be clearly organised, logical and coherent, using appropriate specialist vocabulary correctly. The form and style of writing must be appropriate to answer the question.

Content required:

Names strong, weak and electromagnetic interactions.

Identifies that:

- only hadrons (baryons and mesons) experience the strong interaction

- hadrons and leptons experience weak interaction.

- charged particles experience electromagnetic interaction.

Identifies all exchange particles - gluons (for the strong interaction), W+ and W- bosons (for the weak interaction) and virtual photons (for the electromagnetic interaction).

Gives examples of two of the interactions i.e. electrons repelling, electron capture, beta decay.

Intermediate Level (Modest to adequate): 3 or 4 marks

The information conveyed by the answer may be less well organised and not fully coherent.

There is less use of specialist vocabulary, or specialist vocabulary may be used incorrectly. The form and style of writing is less appropriate.

Low Level (Poor to limited): 1 or 2 marks

The information conveyed by the answer is poorly organised and may not be relevant or coherent. There is little correct use of specialist vocabulary. The form and style of writing may be only partly appropriate.

The examiner was told to use a grid to help check whether the candidate had made all of the relevant points in the answer. The assessor would then have to apply the requirement for good communication of the ideas to the 'grid' marking method. Just making the correct statements without coherence would not get you top marks.

interaction type	strong	weak	electromagnetic
experienced by	only hadrons (baryons and mesons)	hadrons and leptons	charged particles
exchange particle	gluon (pion was allowed instead of gluon - see gluon info)	W+ and W- bosons	virtual photon
example	responsible for binding protons/neutrons/baryons together	beta decay	electrons/protons repelling each other

 

Lower band

1 mark – names two interactions

OR one interaction and one property for that interaction

2 marks – names two interactions and one property for one interaction

Middle band

3 marks - names two interactions plus two properties

4 marks – names two interactions plus minimum of four properties (e.g. 3 properties plus 1 interaction

OR 2 properties plus 2 interactions), if three interactions quoted then properties can be spread between the 3 e.g. one property for each (3) plus one additional

Top band

5 marks – 3 interactions plus two properties for each (9 )

6 marks – must give first two properties for all three interactions AND correctly state two examples of interactions e.g. electron capture example of weak, strong nuclear responsible for binding protons/neutrons/baryons together (11 )

[6 marks]

(b) Draw a labelled Feynman diagram that represents a particle interaction

Any of the Feynman diagrams you are expected to learn for the syllabus were acceptable for this answer. The marks were allocated as follows:

first mark conservation at left hand junction of charge, baryon and lepton number

second mark conservation at right hand junction of charge, baryon and lepton number

third mark for correct exchange particle

[3 marks]

(Total 9 marks)