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AQA A-Level Physics > Chapter 2 - Quarks and Leptons > Flashcards

Chapter 2 - Quarks and Leptons Flashcards

1
Q

What are cosmic rays?

A

High-Energy particles that travel through space from stars

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2
Q

What happens when cosmic rays enter the Earth’s atmosphere?

A
  • Collide with gas atoms
  • Create new short-lived particles and anti-particles, as well as photons
  • Showers of these particles can be detected at ground level
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3
Q

What are most cosmic rays made up of?

A

Fast-moving protons or small nuclei

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4
Q

What is a muon (μ)?

A
  • Heavy electron
  • Rest mass over 200 times the rest mass of the electron
  • Negatively charged
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5
Q

What is a pion/π meson?

A
  • Can be positively charged (π+), negatively charged (π-), or neutral (π0)
  • Rest mass greater than a muon but less than a proton
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6
Q

What is a Kaon/K meson?

A
  • Can be positively charged (K+), negatively charged (K-), or neutral (K0)
  • Rest mass greater than a pion but less than a proton
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7
Q

How are pions and kaons created?

A
  • Produced in twos through the strong interaction
  • Protons moving at high speed crash into nuclei
  • Travel far beyond the nucleus in which they originate before they decay
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8
Q

Why are kaons known as strange particles?

A
  • Decay of kaons took much longer than expected
  • Decay included pions as the product
  • Therefore must decay via the weak interaction
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9
Q

How are strange particles created?

A
  • Created in particle accelerators
  • Protons collide head on with other protons at high speed
  • Kinetic energy of protons converted into mass
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10
Q

What can a Kaon decay into?

A
  • Pions, or
  • A muon and an antineutrino, or
  • An antimuon and a neutrino
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11
Q

What can a charged pion decay into?

A
  • A muon and an antineutrino, or
  • An antimuon and a neutrino
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12
Q

What can a neutral pion decay into?

A

High energy photons

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13
Q

What can a muon decay into?

A

A muon neutrino, an electron and an electron antineutrino

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14
Q

What can an antimuon decay into?

A

A muon antineutrino, a positron and an electron neutrino

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15
Q

What can a proton interact by?

A
  • Strong nuclear force
  • Weak nuclear force
  • Electromagnetic force
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16
Q

What can a neutron interact by?

A
  • Strong nuclear force
  • Weak nuclear force
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17
Q

What can an electron interact by?

A
  • Weak nuclear force
  • Electromagnetic force
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18
Q

What can a neutrino interact by?

A
  • Weak nuclear force
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19
Q

What can a muon interact by?

A
  • Weak nuclear force
  • Electromagnetic force
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20
Q

What can pions interact by?

A
  • Strong nuclear force
  • Weak nuclear force
  • Electromagnetic force (π+, π-)
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21
Q

What can kaons interact by?

A
  • Strong nuclear force
  • Weak nuclear force
  • Electromagnetic force (K+, K-)
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22
Q

What are Hadrons?

A
  • Particles and antiparticles that can interact through the strong nuclear force
  • Interact through all four fundamental forces
  • Protons, Neutrons, π mesons, K mesons
  • Strong and heavy
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23
Q

What are Leptons

A
  • Particles and antiparticles that cannot interact through the strong nuclear force
  • Interact through weak, gravitational and electromagnetic (if charged) interactions
  • Light and weak
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24
Q

How do hadrons tend to decay?

A

Through the weak interaction
- Apart from protons, which are stable

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25
Q

Total energy before a collision equation

A

Total energy of particles and antiparticles before a collision = total rest energy + total kinetic energy

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26
Q

Total energy after a collision equation

A

Total energy of particles and antiparticles after a collision = total rest energy + total kinetic energy

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27
Q

Rest energy of products equation

A

Rest energy of products = total energy before - kinetic energy of the products

28
Q

What are baryons?

A
  • Hadrons that decay into protons, either directly or indirectly
  • Protons, neutrons
29
Q

What are mesons?

A
  • Hadrons that do not include protons in their decay products
  • Short-lived particles with greater rest masses than protons
  • Kaons, pions
30
Q

What can leptons and anti-leptons interact to produce?

A
  • Hadrons
  • Produce a quark and antiquark, which move away in opposite directions and produce a shower of hadrons
31
Q

How can neutrinos differ from each other?

A
  • Neutrinos and antineutrinos produced in beta decays are different from those produced in muon decays
  • Those from muon and antimuon decay create only muons and no electrons when they interact with protons and neutrons
  • If there were only one type of neutrino and antineutrino, equal numbers of electrons and muons would be produced
  • Muon neutrino - ν (μ)
  • Electron neutrino - v (e)
32
Q

Lepton rules

A

Leptons:
- Can change into other leptons through the weak interaction
- Can be produced or annihilated in particle-antiparticle interaction
- Cannot break down into non-leptons - are fundamental

33
Q

What is a lepton number?

A

+1 for any lepton
-1 for any antilepton
0 for any non-lepton

34
Q

Lepton-Hadron interaction

A

In an interaction between a lepton and a hadron, a neutrino or antineutrino can change into a corresponding charged lepton

v(e) + n → p + e-
- LHS lepton number +1, RHS lepton number +1

ν(e) + n ⇏ ˉp + e+
- LHS lepton number +1, RHS lepton number -1 (positron)

35
Q

What happens in muon decay?

A

The muon changes into a muon neutrino. An electron is created to conserve charge and a corresponding antineutrino to conserve lepton number

μ- → e- + ˉv(e) + v(μ)
- LHS charge -1, RHS charge -1
- LHS lepton number +1, RHS lepton number +1

36
Q

Why is μ- → e- + v(e) + ˉv(μ) not possible?

A
  • A muon can only change into a muon neutrino, not a muon antineutrino
  • An electron can only be created with an electron antineutrino
37
Q

Decay and creation of strange particles

A
  • All decay through the weak interaction
  • Those that decay into pions only are kaons
  • Others, such as the sigma particle, were found to:
    • Have different rest masses greater than that of a proton
    • Decay in sequence or directly into protons and pions
  • Strange particles are created in twos
38
Q

When does conservation of strangeness apply?

A
  • Strangeness is always conserved in a strong interaction
  • Strangeness can change by 0, +1, or -1 in weak interactions
39
Q

What are quarks and antiquarks?

A

Smaller particles that make up other particles

40
Q

Properties of an up quark (u)

A
  • Charge +2/3
  • Strangeness 0
  • Baryon number +1/3
41
Q

Properties of a down quark (d)

A
  • Charge -1/3
  • Strangess 0
  • Baryon number +1/3
42
Q

Properties of a strange quark (s)

A
  • Charge -1/3
  • Strangeness -1
  • Baryon number +1/3
43
Q

Properties of an up antiquark (ˉu)

A
  • Charge -2/3
  • Strangeness 0
  • Baryon number -1/3
44
Q

Properties of a down antiquark (ˉd)

A
  • Charge +1/3
  • Strangeness 0
  • Baryon number -1/3
45
Q

Properties of a strange antiquark (ˉs)

A
  • Charge +1/3
  • Strangeness +1
  • Baryon number -1/3
46
Q

Quark composition of a meson

A
  • Mesons are hadrons, each consisting of a quark and an antiquark
  • The antiparticle of a meson is still a quark-antiquark pair and therefore another meson
47
Q

Quark composition of a π- meson

A

dˉu:
Charge -1
Strangeness 0
Baryon number 0

48
Q

Quark composition of a π+ meson

A

uˉd:
Charge +1
Strangeness 0
Baryon number 0

49
Q

Quark composition of a π0 meson

A

uˉu or dˉd:
Charge 0
Strangeness 0
Baryon number 0

*sˉs not called pions as they decay much faster than pions

50
Q

Quark composition of a K+ meson

A

uˉs:
Charge +1
Strangeness +1
Baryon number 0

51
Q

Quark composition of a K- meson

A

sˉu:
Charge -1
Strangeness -1
Baryon number 0

52
Q

Quark composition of a K0 meson

A

dˉs:
Charge 0
Strangeness +1
Baryon number 0

53
Q

Quark composition of a ˉK0 meson

A

sˉd
Charge 0
Strangeness -1
Baryon number 0

54
Q

Quark composition of baryons

A

Three quarks

55
Q

Quark composition of antibaryons

A

Three antiquarks

56
Q

Quark composition of a proton

A

uud
Charge +1
Strageness 0
Baryon number +1

57
Q

Quark composition of a neutron

A

udd
Charge 0
Strangeness 0
Baryon number +1

58
Q

Quark composition of an antiproton

A

ˉuˉuˉd
Charge +1
Strangeness 0
Baryon numver -1

59
Q

Quark composition of an antineutron

A

ˉuˉdˉd
Charge 0
Strangeness 0
Baryon number -1

60
Q

What does a neutron decay into?

A

A proton, releasing an electron and an electron antineutrino (β- decay)

61
Q

β- decay in quark terms

A

A down quark changes into an up quark:
- neutron changes into a proton, releasing an electron and an electron antineutrino

62
Q

β+ decay in quark terms

A

An up quark changes into a down quark:
- proton changes into a neutron, releasing a positron and an electron neutrino

63
Q

What is the conservation of lepton numbers?

A

In any change, the total lepton number for each lepton branch is equal to the total lepton number for that branch after the change

*muon lepton number and electron lepton number must both be conserved - they are not the same thing

64
Q

What is the conservation of strangess?

A

In any strong interaction, strangeness is always conserved

65
Q

What is the conservation of baryon numbers?

A

In any reaction, the total baryon number of the individual quarks is conserved

AQA A-Level Physics (4 decks)

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