Particle Physics Questions
Q9.
(a)
(i) Name two baryons.
Any two, eg, proton, neutron
(1 mark)
(ii) State the quark structure of the pion π+
u ̅d
(1 mark)
(b) The K+ kaon is a strange particle.
(i) Give one characteristic of a strange particle that makes it different from a particle that is not strange.
It contains a strange quark
or
It has a longer half-life than expected
or
It decays via a weak interaction
(1 mark maximum)
(ii) One of the following equations represents a possible decay of the K+ kaon.
K+ → π+ + π0
K+ → µ+ + v µ
State, with a reason, which one of these decays is not possible.
(2 marks)
(c) Another strange particle, X, decays in the following way:
X → π – + p
(i) State what interaction is involved in this decay.
Weak nuclear interaction
(1 mark)
(ii) Show that X must be a neutral particle.
Charge is always conserved.
The products are a negative pion and a proton (which is positive) therefore the net product charge is zero. The particle X must therefore be neutral (have zero charge).
(1 mark)
(iii) Deduce whether X is a meson, baryon, or lepton, explaining how you arrive at your answer.
X must be a baryon as the proton is a baryon making the baryon number of the products +1 and baryon number has to be conserved, the baryon number of X must also be +1.
(2 marks)
(iv) Which particle in this interaction is the most stable?
The proton
(1 mark)
(Total 10 marks)
About this site
No strange particles in the products so strangeness is not conserved - therefore weak not strong...
