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Particle Physics Questions

Q8. The κ– meson has strangeness –1.

(a) State the quark composition of a meson.

A quark–antiquark pair (or this can be written q and ̅q - but it is best to write in good English than to use abbreviations)

(1 mark)

(b) State the baryon number of the κ– meson.

0 (it is not a baryon so the baryon number is zero)

(1 mark)

(c) What is the quark composition of the κ– meson?

It is negative so charge overall must be negative - therefore you need the strange quark to be a quark not an antiquark... that means you need another -2/3 to make up a charge of -1, so you need an anti-up.

̅u s

 

(1 mark)

(d) Complete this equation for the decay of a κ– meson.

κ– → _ _ _ _ + _ _ _ _ + _ _ _ _

When a kaon decays it does so via a weak interaction and strangeness is not conserved.

There will be a lepton involved (weak interaction) so either an electron or muon will be produced (because the kaon is negative).... together with an antilepton (to conserve lepton number).

The strangness is not conserved, so a pion will be formed - having to be neutral as the charge went to the lepton.

κ– → π0 + e– + ̅νe

 

or

 

κ– → π0 + µ– + ̅ν µ

(2 marks)

(Total 5 marks)