Particle Physics - energy and mass

Question 1

What is the name of the event where energy is converted into mass?

Answer 1

Creation Events

Question 2

What is the name of the event where mass is converted into energy?

Answer 2

Annihilation Events

Question 3

What is the composition of a proton? And what about an antiproton?

Answer 3

• Proton; x2 up, x1 down

- Antiproton: x2 anti-up, x1 anti-down

Question 4

What is the composition of a neutron? And what about an antineutron?

Answer 4

• Neutron: x1 up, x2 down

- Antineutron: x1 anti-up, x2 anti-down

Question 5

What three things must be conserved in creation/annihilation/decay events?

Answer 5

• Baryons; number of baryons
• Leptons; number of leptons
• Charge; total charge

Question 6

State whether this event is possible (considering conservation laws);

(p) + (e) -> (n)

Answer 6

Proton + electron -> neutron

• Charge; (+1) + (-1) -> (0)
• Baryons; (+1) + (0) -> (+1)
• Leptons; (0) + (+1) -> (0)

Leptons are not conserved in this event.

Question 7

State whether this event is possible (considering conservation laws);

(γ) -> (e^-)

Answer 7

Gamma -> electron

• Charge; (0) -> (-1)
• Baryons; (0) -> (0)
• Leptons; (0) -> (+1)

Charge and leptons are not conserved in this event.

Question 8

State whether this event is possible (considering conservation laws);

(π^0) -> (p) + (p bar)

Answer 8

Pion -> proton + antiproton

• Charge; (0) -> (+1) + (-1)
• Baryons; (0) -> (+1) + (-1)
• Leptons; (0) -> (0) + (0)

All are conserved in this event.

Question 9

State whether this event is possible (considering conservation laws);

(n bar) + (γ) -> (p bar) + (e^+)

Answer 9

Antineutron + gamma -> antiproton + positron

• Charge; (0) + (0) -> (-1) + (+1)
• Baryons; (-1) + (0) -> (-1) + (0)
• Leptons; (+1) + (0) -> (-1) + (+1)

Leptons are not conserved in this event.

Question 10

State whether this event is possible (considering conservation laws);

(K^+) -> (μ^+) + (ν of μ)

Answer 10

Kaon* -> positive muon + muon neutrino
*don’t think you actually have to remember this so don’t worry

• Charge; (+1) -> (+1) + (0)
• Baryons; (0) -> (0) + (0)
• Leptons; (0) -> (-1) + (+1)

All are conserved in this event.

Question 11

State whether this event is possible (considering conservation laws);

(uud) -> (u (d bar)) + (udd)

Answer 11

Up Up Down -> Up Anti-down + Up Down Down

• Charge;
  uud: (+2/3 e +2/3 e -1/3 e) = + e
  u d-bar: (+2/3 e +1/3 e) = + e
  udd: (+2/3 e -1/3 e -1/3 e) = 0
  … so …
  (+e) -> (+e) + 0
• Baryons; (+1) -> (0) + (+1)
• Leptons; (0) -> (0) + (0)

All are conserved in this event.

Question 12

In this event;

(p) + (e) -> (n)

Leptons are not conserved.

How can you conserve leptons in this example and in what form will they come? Basically, how would the equation be balanced.

Answer 12

Product will have a neutrino as well as the neutron to balance leptons.

The conservation equation;

(p) + (e) -> (n) + (ν any)