Quarks and Leptons

Question 1

For a proton, give:

i) the symbol
ii) charge
iii) its antiparticle, charge and symbol
iv) rest energy (in MeV)
v) interactions it is involved in

Answer 1

i) p
ii) +1
iii) antiproton, -1, p̄
iv) 938
v) Strong, weak decay, electromagnetic

Question 2

For a neutron, give:

i) the symbol
ii) charge
iii) its antiparticle, charge and symbol
iv) rest energy (in MeV)
v) interactions it is involved in

Answer 2

i) n
ii) 0
iii) antineutron, 0, n̄
iv) 939
v) Strong, weak decay

Question 3

For an electron, give:

i) the symbol
ii) charge
iii) its antiparticle, charge and symbol
iv) rest energy (in MeV)
v) interactions it is involved in

Answer 3

i) e⁻
ii) -1
iii) positron, +1, e⁺
iv) 0.511
v) weak, electromagnetic

Question 4

For a neutrino, give:

i) the symbol
ii) charge
iii) its antiparticle, charge and symbol
iv) rest energy (in MeV)
v) interactions it is involved in

Answer 4

i) ν
ii) 0
iii) antineutrino, 0, v̅
iv) 0
v) weak

Question 5

For a muon, give:

i) the symbol
ii) charge
iii) its antiparticle, charge and symbol
iv) rest energy (in MeV)
v) interactions it is involved in

Answer 5

i) μ⁻
ii) -1
iii) antimuon, +1, μ⁺
iv) 106
v) weak, electromagnetic

Question 6

For a pi messon, give:

i) the symbol
ii) charge
iii) its antiparticle, charge and symbol
iv) rest energy (in MeV)
v) interactions it is involved in

Answer 6

i) π⁺, π⁰, π⁻
ii) +1, 0, -1
iii) π⁺ for π⁻
π⁻ for π⁺
π⁰ for π⁰
iv) 140, 135, 140
v) strong, electromagnetic (for π⁺, π⁻)

Question 7

For a K messon, give:

i) the symbol
ii) charge
iii) its antiparticle symbol
iv) rest energy (in MeV)
v) interactions it is involved in

Answer 7

i) K⁺, K⁰, K⁻
ii) +1, 0, -1
iii) K⁺ for K⁻
K⁻ for K⁺
K⁰ for K̅⁰
iv) 494, 498, 494
v) strong, electromagnetic (for K⁺, K⁻)

Question 8

What 2 categories do matter and antimatter split into ?

Answer 8

Hadrons and Leptons

Question 9

What 2 categories do hadrons split into?

Answer 9

Baryons and Mesons

Question 10

Define a baryon

Answer 10

Baryons are protons and all other hadrons (including neutrons) that decay into protons, either directly or indirectly

Question 11

Define a meson

Answer 11

Mesons are hadrons that do not include protons in their decay products (e.g. K and π mesons)

Question 12

For the collision of 2 particles, using the conservation of energy, give the equation for the rest energy of the products

Answer 12

Product rest E = Total E before - KE of products

Question 13

What is 1 GeV equal to in MeV?

Answer 13

1000 MeV

Question 14

Describe the quark composition for a baryon

Answer 14

3 quarks or 3 antiquarks

Question 15

Describe the quark composition for a meson

Answer 15

A quark and an anti-quark

Question 16

Give the quark composition for a:

i) proton
ii) antiproton

Answer 16

i) p = uud

ii) p̄ = ūūd̄

Question 17

Give the quark composition for a:

i) neutron
ii) antineutron

Answer 17

i) n = udd

ii) n̄ = ūd̄d̄

Question 18

Give the quark composition for:

i) π⁺
ii) π⁻
iii) π⁰

Answer 18

i) π⁺ = ud̄
ii) π⁻ = ūd
iii) π⁰ = uū or dd̄

Question 19

Give the quark composition and strangeness for:

i) K⁺
ii) K⁻
iii) K⁰
iv) K̄⁰

Answer 19

i) K⁺ = us̄ (Strangeness +1)
ii) K⁻ = ūs (Strangeness -1)
iii) K⁰ = ds̄ (Strangeness +1)
iv) K̄⁰ = d̄s (Strangeness -1)

Question 20

Give the 3 types of leptons (not including neutrinos or anti-leptons)

Answer 20

e⁻ (Electron)
μ⁻ (Muon)
τ⁻ (Tau)

Question 21

Give the products for the reaction between a neutrino/anti-neutrino and a hadron and give an example

Answer 21

The neutrino/anti-neutrino can change into or form a corresponding charged lepton

                        e.g. νₑ + n →p + e⁻

Question 22

Give the products for the decay of a muon

Answer 22

A muon neutrino, an electron and an anti-electron neutrino

μ⁻ → e⁻ + νₑ + ν(μ)

Question 23

State the conservation of lepton number

Answer 23

The lepton number is always conserved

Question 24

In what interactions is strangeness always conserved?

Answer 24

Strong interactions

Question 25

State the 3 types of quark, and give their charge and strangeness

Answer 25

Up (u), charge +⅔, strangeness 0
Down (d), charge -⅓, strangeness 0
Strange (s), charge -⅓, strangeness -1

Question 26

Describe β⁻ decay in terms of quarks

Answer 26

In a neutron-rich nucleus, a down quark changes into an up quark, releasing a β⁻ particle and a ν̄ₑ. It interacts by the W⁻ force

Question 27

Describe β⁺ decay in terms of quarks

Answer 27

In a proton-rich nucleus, an up quark changes into a down quark, releasing a β⁺ particle and a νₑ. It interacts by the W⁺ force

Question 28

Give the rules of conservation for all particle interactions

Answer 28

• Energy is conserved (in all changes)
• Lepton number is always conserved
• Baryon number is always conserved
• Strangeness is conserved in any strong interaction