Particle Physics [97 marks]

1. Which is the correct Feynman diagram for pair annihilation and pair production?

2. What is correct about the Higgs Boson?

A. It was predicted before it was observed.

B. It was difficult to detect because it is charged.

C. It is not part of the Standard Model.

D. It was difficult to detect because it has no mass.

3. A particle of fixed energy is close to a potential barrier.

Which changes to the width of the barrier and to the height of the barrier will always make thetunnelling probability greater?

Identify the conservation law violated in the proposed reaction.

[1 mark]

[1 mark]

[1 mark]

4. Identify the conservation law violated in the proposed reaction.

p + p → p + n + µ

A. Strangeness

B. Lepton number

C. Charge

D. Baryon number

+ + + 0 +

5a.

The Feynman diagram shows electron capture.

Deduce that X must be an electron neutrino.

5b. Distinguish between hadrons and leptons.

State the quark structures of a meson and a baryon.

[1 mark]

[2 marks]

[2 marks]

6a. State the quark structures of a meson and a baryon.

6b.

A possible decay of a lambda particle ( ) is shown by the Feynman diagram.

Explain which interaction is responsible for this decay.

Λ0

6c. Draw arrow heads on the lines representing and d in the .u π−

6d. Identify the exchange particle in this decay.

[2 marks]

[2 marks]

[1 mark]

[1 mark]

6e. Outline one benefit of international cooperation in the construction or use of high-energy particle accelerators.

7a. A particular K meson has a quark structure s. State the charge, strangeness andbaryon number for this meson.

u

7b. The Feynman diagram shows the changes that occur during beta minus (β ) decay.

Label the diagram by inserting the four missing particle symbols and the direction of the arrowsfor the decay particles.

–

C-14 decay is used to estimate the age of an old dead tree. The activity of C-14 in the

[1 mark]

[2 marks]

[3 marks]

7c. C-14 decay is used to estimate the age of an old dead tree. The activity of C-14 in thedead tree is determined to have fallen to 21% of its original value. C-14 has a half-lifeof 5700 years.

(i) Explain why the activity of C-14 in the dead tree decreases with time.

(ii) Calculate, in years, the age of the dead tree. Give your answer to an appropriate number ofsignificant figures.

8a.

In beta minus (β ) decay a d quark decays into a u quark, an electron and an electronantineutrino.

Show that lepton number is conserved in this decay.

−

32 −

[4 marks]

[1 mark]

8b. A nucleus of phosphorus-32 decays by beta minus (β ) decay into a nucleus ofsulfur-32 . The binding energy per nucleon of is 8.398 MeV and for it is 8.450MeV.

(i) State what is meant by the binding energy of a nucleus.

(ii) Determine the energy released in this decay.

(3215P) −

(3216S) 32

15P 3216S

8c. Quarks were hypothesized long before their existence was experimentally verified.Discuss the reasons why physicists developed a theory that involved quarks.

9. Which Feynman diagram shows beta-plus (β ) decay?+

The reaction p + n → p + does not occur because it violates the conservation law+ 0 + 0

[3 marks]

[3 marks]

[1 mark]

10. The reaction p + n → p + does not occur because it violates the conservation lawof

A. electric charge.

B. baryon number.

C. lepton number.

D. strangeness.

+ 0 + π0

11. As quarks separate from each other within a hadron, the interaction between thembecomes larger. What is the nature of this interaction?

A. ElectrostaticB. Gravitational C. Strong nuclear D. Weak nuclear

12. Which particle is acted on by both the strong nuclear force and the Coulomb force?

A. AntineutrinoB. ElectronC. NeutronD. Proton

13. Which of the following is a correct list of particles upon which the strong nuclear forcemay act?

A. protons and neutronsB. protons and electronsC. neutrons and electronsD. protons, neutrons and electrons

14. Protons and neutrons are held together in the nucleus by the

A. electrostatic force.

B. gravitational force.

C. weak nuclear force.

D. strong nuclear force.

This question is about interactions and quarks.

[1 mark]

[1 mark]

[1 mark]

[1 mark]

[1 mark]

15a.

This question is about interactions and quarks.

A lambda baryon is composed of the three quarks uds. Show that the charge is 0and the strangeness is .

Λ0

−1

15b.

For the lambda baryon , a student proposes a possible decay of as shown.

The quark content of the meson is .

Discuss, with reference to strangeness and baryon number, why this proposal isfeasible.

Strangeness:

Baryon number:

Λ0 Λ0

Λ0 → p + K −

K − us

[2 marks]

[4 marks]

15c. Another interaction is

In this interaction strangeness is found not to be conserved. Deduce the nature of thisinteraction.

Λ0 → p + π−

16a.

This question is about particle interactions.

An electron and a positron interact to produce a muon and antimuon through a weak interaction.The weak interaction involves one of the virtual particles , or boson.

Describe what is meant by a virtual particle.

W− W+ Z0

16b. Draw a Feynman diagram which represents this interaction.

16c. Explain whether this interaction involves the , or boson.W− W+ Z0

This question is about quarks.

[1 mark]

[1 mark]

[2 marks]

[1 mark]

17a.

This question is about quarks.

An interaction between an electron and a positron can lead to the production of hadrons via thereaction

where u is an up quark. This process involves the electromagnetic interaction.

Draw a Feynman diagram for this interaction.

e− + e+ → u + u

17b. Outline, with reference to the strong interaction, why hadrons are produced in thereaction.

18.

This question is about particles and interactions.

When a free neutron decays to a proton, an electron is one of the decay products.

(i) State the name of the exchange particle and the interaction involved in this decay.

(ii) The interaction and the exchange particle in (a)(i) may arise when a quark decays. Describethe change in the quark structure of the neutron.

This question is about a K meson decay.

[2 marks]

[2 marks]

[2 marks]

19a.

This question is about a K meson decay.

The positive kaon K has a strangeness of +1. It can decay through the interaction

K → µ + ν .

Charge, energy and momentum are conserved in this decay.

State the quark structure of the K .

+

+ +µ

+

19b. Deduce one further quantity in this decay that is

(i) conserved.

(ii) not conserved.

20a.

This question is about particles and interactions.

(i) State what is meant by an antiparticle.

(ii) Some particles are identical to their antiparticles. Discuss whether the neutron and theantineutron are identical.

The Feynman diagram represents the decay .− → ++ −+ −

[1 mark]

[2 marks]

[3 marks]

20b. The Feynman diagram represents the decay .

Particles X and Y are exchange particles.

(i) Explain what is meant by an exchange particle.

(ii) Identify X.

(iii) Determine the electric charge of Y.

(iv) Calculate the change in strangeness in the decay of the K .

K − → π++π−+π−

–

This question is about particles.

[5 marks]

21a.

This question is about particles.

The Σ particle can decay into a π particle and another particle Y as shown in theFeynman diagram.

(i) Identify the exchange particle X.

(ii) Identify particle Y.

(iii) Outline the nature of the π .

+ 0

0

The π particle can decay with the emission of two gamma rays, each one of which0

[4 marks]

21b. The π particle can decay with the emission of two gamma rays, each one of whichcan subsequently produce an electron and a positron.

(i) State the process by which the electron and the positron are produced.

(ii) Sketch the Feynman diagram for the process in (c)(i).

0

21c. Discuss whether strangeness is conserved in the decay of the Σ particle in (a).+

22a.

This question is about elementary particles.

This quark is said to be an elementary particle.

State what is meant by the term elementary particle.

The strong interaction between two nucleons has a range of about 10 m.–15

[3 marks]

[1 mark]

[1 mark]

22b. The strong interaction between two nucleons has a range of about 10 m.

(i) Identify the boson that mediates the strong interaction.

(ii) Determine the approximate mass of the boson in (b)(i).

–15

23.

This question is about particle production.

In a particular experiment, moving kaon mesons collide with stationary protons. Thefollowing reaction takes place

where X is an unknown particle. This process involves the strong interaction. Thequark structure of the kaons is , , and .

(i) State the strangeness of the unknown particle X.

(ii) Particle X is a hadron. State and explain whether X is a meson or a baryon.

p + K − → K 0 + K + + X

K − = us K 0 = ds K + = us

24a.

This question is about quarks.

State the name of a particle that is its own antiparticle.

0 0

[3 marks]

[3 marks]

[1 mark]

24b. The meson K consists of a d quark and an anti s quark. The K decays into two pionsas shown in the Feynman diagram.

(i) State a reason why the kaon K cannot be its own antiparticle.

(ii) Explain how it may be deduced that this decay is a weak interaction process.

(iii) State the name of the particle denoted by the dotted line in the diagram.

(iv) The mass of the particle in (b)(iii) is approximately 1.6×10 kg. Determine the range of theweak interaction.

0 0

0

–25

25a.

This question is about the decay of a kaon.

A kaon (K ) is a meson consisting of an up quark and an anti-strange quark.

Suggest why the kaon is classified as a boson.

+

A kaon decays into an antimuon and a neutrino, K →µ +v . The Feynman+ +

[6 marks]

[2 marks]

25b. A kaon decays into an antimuon and a neutrino, K →µ +v . The Feynmandiagram for the decay is shown below.

(i) State the two particles labelled X and Y.

(ii) Explain how it can be deduced that this decay takes place through the weak interaction.

(iii) State the name and sign of the electric charge of the particle labelled A.

+ +

26.

This question is about the early universe and the Higgs boson.

The graph shows the variation of the logarithm of the temperature T of the universe with thelogarithm of the time t after the Big Bang.

Evidence for the Higgs boson might be discovered at the Large Hadron Collider(LHC) at CERN. Outline why such a discovery would be of crucial significance tothe standard model.

[6 marks]

[2 marks]

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