Quarks and leptons (topic 2) Flashcards

1
Q

What are cosmic rays?

A

High-energy particles (protons or small nuclei) travelling through space, from stars

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2
Q

What happens when cosmic rays enter the atmosphere?

A

They collide with gas atoms in the atmosphere, creating photons, and new short-lived particles and anti-particles

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3
Q

What are the three short-lived particles created by cosmic rays reaching earth’s atmosphere or protons colliding at high speeds?

A

Muon, pion, kaon

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4
Q

What are the characteristics of the muon? (2)

A
  • negatively charged
  • rest mass 200x larger than an electron
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5
Q

What are the characteristics of a pion? (2)

A
  • Can have positive, negative or neutral charge
  • rest mass greater than muon but less than proton
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6
Q

What are the characteristics of a kaon? (3)

A
  • can have positive, negative or neutral charge
  • rest mass greater than pion but less than proton
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7
Q

What is created by kaon decay? (2)

A

1) pions

2) muon antineutrino/neutrino antimuon pair

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8
Q

What is created by CHARGED pion decay?

A

muon antineutrino/neutrino antimuon pair

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9
Q

What is created by pion(0) decay?

A

high-energy photons

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10
Q

What is creates by muon decay?

A

electron and antineutrino

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11
Q

Hadrons (definition)

A

Particles/antiparticles that can interact through strong interaction
and are made up of quarks

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12
Q

Leptons (definition)

A

Particles/anitparticles that do NOT interact through the strong interaction and are NOT made up of quarks

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13
Q

What is conserved in ALL decays? (5)

A

Energy, momentum, charge, lepton number, baryon number

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14
Q

How do we find the rest energy of products of interactions?

A

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

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15
Q

Baryon (definition)

A

Hadrons that decay into protons (directly or indirectly)

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16
Q

Meson (definition)

A

Hadrons that cannot decay into protons (kaons and pions)

17
Q

What happens when leptons collide?

A

A quark and its antiqaurk are produced moving in opposite direction, producing a “shower” of hadrons in each direction.

18
Q

How are electron neutrinos and muon neutrinos different?

A

Muon neutrinos can only create muons. They cannot create electrons when interacting with protons/neutrons.

19
Q

What do current experiments indicate about leptons? How do we come to this conclusion?

A

Leptons appear to be fundamental, because they cannot break down into non-leptons

20
Q

Why can a neutrino only change into its corresponding lepton, not its corresponding antilepton?

A

Lepton number must be conserved. Anti leptons have lepton number -1, so must produce a particle with lepton number -1 in a lepton-hadron interaction.

21
Q

What happens in muon decay?

A

A muon becomes a muon neutrino/antimuon to antineutrino, and a electron/positron is created to conserve the charge + relevant (anti)neutrino. A muon cannot become an antimuon neutrino because lepton number or charge could not be conserved.

22
Q

How does lepton conservation work?

A

Leptons have lepton number +1, antileptons have lepton number -1. Electrons and muons + their respective neutrinos must be considered respectively as muon neutrinos can’t become electrons and vice versa.

23
Q

How is a kaon different from other strange particles?

A

It only decays into pions and has a rest mass lower than that of a proton.

24
Q

What is true for all strange particles?

A

They are produced in twos and decay through the weak interaction

25
How is strangeness conserved? (2)
Always conserved in strong interactions Can change by +1, -1 or not change during weak interactions
26
Properties of an u quark (3)
Charge = +2/3 Strangeness = 0 Baryon number = +1/3
27
Properties of a d quark (3)
Charge = -1/3 Strangeness = 0 Baryon number = +1/3
28
Properties of an s quark (3)
Charge = -1/3 Strangeness = -1 Baryon number = +1/3
29
Meson quark combinations
A quark-anti-quark pair
30
Baryon quark combinations
Three quarks OR three antiquarks
31
Which baryons are stable?
Only the proton - neutrons outside the nucleus will decay into protons through beta(-)
32
Kaon quark combinations
Kaons must include an (anti)/strange quark. Positive and K(0) have +1S, while anti-positive and anti(K(0)) have -1S.
33
Pion quark combinations
Only contain anti(up/down) quarks. All antimesons are also mesons, so pion+ is the antimeson of pion- and there are two pion(0)s.
34
Which baryon is the only one to include a strange particle?
Sigma
35
Where does beta(-) decay happen? Where does beta(+) decay happen?
B- = in a neutron-rich nucleus B+ = in a proton-rich nucleus
36
What happens in terms of quarks during beta- decay?
A down quark changes to an up quark
37
What must be conserved in STRONG interactions? (6)
Charge, energy, momentum, lepton number, baryon number, and strangeness
38
Why might number of quarks NOT be conserved in an interaction?
Annihilation or pair production