 # Particle Physics Questions These questions incorporate several aspects of the particle physics topic.

I have made a separate page of questions that involve you drawing Feynman diagrams. These should be tackled after you have tried the ones on this page.

Q1.

(a) Describe how the strong nuclear force between two nucleons varies with the separation of the nucleons quoting suitable values for separation. (3 marks)

(b) An unstable nucleus can decay by the emission of an alpha particle.

(i) State the nature of an alpha particle.  (1 mark)

(ii) Complete the equation below to represent the emission of an alpha particle by a uranium nucleus. (2 marks)

(c) Uranium 238 decays in stages by emitting particles and particles, eventually forming a stable isotope of lead, called lead 206.

(i) State what is meant by 'isotope'. (2 marks)

(ii) If there are eight alpha decays involved in the sequence of decays from uranium 238 to lead 206 deduce how many decays are involved. (show your working!) (3 marks)

(Total 11 marks) Q2.

(a) Hadrons are a group of particles composed of quarks. Hadrons can either be baryons or mesons.

(i) What property defines a hadron?

(ii) What is the quark structure of a baryon?

(iii) What is the quark structure of a meson? (3 marks)

(b) State one similarity and one difference between a particle and its antiparticle. (2 marks)

(c) Complete the table below which lists properties of the antiproton.

 Charge/C baryon number quark structure antiproton

(2 marks)

(d) The is an example of a meson with strangeness –1.

It decays in the following way: (i) State, with a reason, what interaction is responsible for this decay. (2 marks)

(ii) State two properties, other than energy and momentum, that are conserved in this decay. (2 marks)

(Total 11 marks) Q3. The table gives information about some fundamental particles.

 particle quark structure charge strangeness baryon number u u d 0 Sigma + u u s + 1 u 0 0

(a) Complete the table by filling in the missing information.

(7 marks)

(b) Each of the particles in the table has an antiparticle.

(i) Give one example of a baryon particle and its corresponding antiparticle.

(1 mark)

(ii) State the quark structure of an antibaryon.

(1 mark)

(iii) Give one property of an antiparticle that is the same for its corresponding particle and one property that is different.

(2 marks)

(Total 11 marks) Q4.

(a) Pair production can occur when a photon interacts with matter. Explain the process of pair production.

(2 marks)

(b) Explain why pair production cannot take place if the frequency of the photon is below a certain value.

(3 marks)

(c) Energy and momentum are conserved during pair production. State two other quantities that must also be conserved.

(2 marks)

(Total 7 marks) Q5.

Sub-atomic particles can either be hadrons or leptons.

(a) State one difference between these two groups of particles.

(1 mark)

(b) Give an example of

(ii) an example of a lepton

(2 marks)

(c) Hadrons can be further divided into two groups. Name these two groups and state a difference between them.

(3 marks)

(Total 6 marks) Q6.

(a) The Σ+ particle is a baryon with strangeness –1.

(i) How many quarks does the Σ+ particle contain?

(1 mark)

(ii) How many of the quarks are strange?

(1 mark)

(b) The Σ+ decays in the following reaction

# Σ+ → π+ + n

(i) State two quantities that are conserved in this reaction.

(2 marks)

(ii) State a quantity that is not conserved in this reaction.

(1 mark)

(iii) What interaction is responsible for this reaction?

(1 mark)

(iv) Into what particle will the neutron formed in this reaction eventually decay?

(1 mark)

(Total 7 marks) Q7.

(a) Mesons that contain a strange (or antistrange) quark are known as K-mesons or kaons. Mesons are a sub-group of a larger group of particles.

(i) State the name of this larger group of particles.

(1 mark)

(ii) Determine the charge on a kaon with a quark structure of u̅ s

(1 mark)

(b) A proposed decay for this kaon is

# ̅u s → µ+ + vµ

(i) Apply the law of conservation of strangeness to the proposed decay.

(1 mark)

(ii) Comment on whether or not this decay is possible.

(1 mark)

(Total 4 marks) Q8. The κ meson has strangeness –1.

(a) State the quark composition of a meson.

(1 mark)

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

(1 mark)

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

(1 mark)

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

# κ– → _ _ _ _ + _ _ _ _ + _ _ _ _

(2 marks)

(Total 5 marks) Q9.

(a)

(i) Name two baryons.

(1 mark)

(ii) State the quark structure of the pion π+

(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.

(1 mark)

(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.

(1 mark)

(ii) Show that X must be a neutral particle.

(1 mark)

(iii) Deduce whether X is a meson, baryon, or lepton, explaining how you arrive at your answer.

(2 marks)

(iv) Which particle in this interaction is the most stable?

(1 mark)

(Total 10 marks) Q10.

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

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

(1 mark)

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

(1 mark)

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

(1 mark)

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

# K+ → vμ + μ+

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

# μ+

lepton   charged particle
meson

(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.

(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 muon negative pion neutral pion neutrino neutron positron

(1 mark)

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

(1 mark)

(Total 10 marks) Q11.

(a) Complete the table comparing some of the properties of the positive pion, π+, and the proton

 Name π+ Proton Relative charge +1 Baryon number Quark composition

(b)     When a positive pion interacts with a proton, a kaon can be produced, along with another strange particle, as shown in this equation What type of interaction is shown in this equation?

(1mark)

(c)     Deduce the relative charge, baryon number and strangeness of particle X.

(3marks)

(d)     Particle X can decay to produce a neutron and positive pion as shown in this equation What type of interaction is shown in this equation?

(1mark)

(2 marks)

(f)     The neutron and positive pion will then decay. The positive pion can decay into a positron and an electron neutrino. Write down the equation for the decay of the neutron.

(2 marks)

(g)     Explain why no further decays occur.

(2 marks)

(Total 16 marks) Q12.

The equation shows an interaction between a proton and a negative kaon that results in the formation of particle, X.

# K– + p → K+ + K0 + X

(a)

(i) State and explain whether X is a charged particle.

[2 marks]

(ii) State and explain whether X is a lepton, baryon or meson.

[2 marks]

(iii) State the quark structure of the K, K+ and the K0.

[3 marks]

(iv) Strangeness is conserved in the interaction. Determine, explaining your answer, the quark structure of X.

[3 marks]