Q10.

(a) The positive kaon, K⁺, has a strangeness of +1.

(i) What is the quark structure of the K⁺?

A kaon is a meson - quark and antiquark structure.

It is strange and positive - therefore the strange quark component of it must be the antistrange. That gives it a charge of +¹/₃ - so the up quark must complete the meson.

u ̅s̅

(1 mark)

(ii) What is the baryon number of the K⁺?

It is not a baryon - so it will have a baryon number of zero - or you can look to the baryone nmber data in the table!

zero

(1 mark)

(iii) What is the antiparticle of the K⁺?

The antiparticle will have the quark-antiquark combination s ̅u̅ - making it a

negative kaon K^-

(1 mark)

(b) The K⁺ may decay into a neutrino and an antimuon in the following way:

K⁺ → v_μ + μ⁺

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

Classification	K+	vμ	μ+
lepton
charged particle
hadron
meson

 

for each correct line

(3 marks)

(ii) In this decay, charge, energy and momentum are conserved. Give another quantity that is conserved in this decay and one that is not conserved.

lepton number or baryon number are conserved

strangeness or kinetic energy is not conserved

(c) Another possible decay of the K+ is shown in the following equation,

K⁺ → π⁺ + X

(2 marks)

(i) Identify X by ticking one box from the following list.

electron	cannot be - it is charged
muon	cannot be - it is charged
negative pion	cannot be - it is charged
neutral pion
neutrino	cannot be - it is a lepton
neutron	cannot be - it is a baryon
positron	cannot be - it is charged

 

(1 mark)

(ii) Give one reason for your choice in part (c)(i).

It must be of neutral charge to obey charge conservation or cannot be a baryon to obey conservation of baryon number or cannot be alepton to obey conservation of lepton number

(1 mark maximum)

(Total 10 marks)