Worksheet: Units for Particle Rest Masses

In this worksheet, we will practice using units of eV/c² to express the masses of subatomic particles and converting between eV/c² and kg.

Q1:

Particle Electron Muon Tauon
Mass 5 1 1 / 𝑐 k e V 1 0 6 / 𝑐 M e V 1 . 7 8 / 𝑐 G e V

The table shows the masses of the three charged leptons. What is the most massive lepton–antilepton pair that could be produced via pair production from a 150 MeV photon?

  • AA tauon–antitauon pair
  • BAn electron–positron pair
  • CA muon–antimuon pair

Q2:

What is 4 . 9 9 × 1 0 kg in keV/ 𝑐 ? Give your answer to 3 significant figures.

Q3:

A muon has a mass of 1 0 6 / 𝑐 M e V . What is the mass of a muon in kilograms? Give your answer to 3 significant figures.

  • A 6 . 3 2 × 1 0 kg
  • B 1 . 6 9 × 1 0 kg
  • C 1 . 6 9 × 1 0 kg
  • D 1 . 8 9 × 1 0 kg
  • E 1 . 8 9 × 1 0 kg

Q4:

The Feynman diagram shows a sigma baryon decaying into a neutron and a pion.

What particle is represented by 𝑋 in the diagram?

  • A ̄ 𝑠
  • B 𝑊
  • C 𝑊
  • D ̄ 𝑑
  • E 𝑑

What particle is represented by 𝑌 in the diagram?

  • A 𝑊
  • B 𝑊
  • C ̄ 𝑠
  • D 𝑑
  • E ̄ 𝑑

Q5:

The Feynman diagram shows an antitauon decaying into an antimuon. What particle is represented by 𝑋 in the diagram?

  • A 𝑔
  • B 𝜇
  • C 𝑊
  • D 𝛾
  • E 𝑊

Q6:

Is the interaction shown in the Feynman diagram possible? If not, why not?

  • AYes
  • BNo, because it doesn’t conserve electric charge
  • CNo, because it doesn’t conserve strangeness
  • DNo, because it doesn’t conserve the baryon number
  • ENo, because a W boson cannot decay into a pion

Q7:

Which of the following Feynman diagrams shows the interaction 𝜏 𝜇 𝜈 𝜈 + + ?

  • A
  • B
  • C
  • D

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