Chapter 2 - Quarks and Leptons

Question 1

How are cosmic rays a source of high energy particles?

Answer 1

Cosmic rays are fast-moving protons or small nuclei. They collide with gas atoms in the atmosphere, creating showers of particles and antiparticles that can be detected by ground level

Question 2

How can cosmic ray showers be detected?

Answer 2

• Use of two geiger counters placed one above the other, separated by absorbing lead.
• If both counters detect radiations simultaneously then it’s most likely that a particle from a cosmic ray shower has been detected

Question 3

What 2 classifications are particles put in?

Answer 3

Hadrons and leptons

Question 4

What are hadrons?

Answer 4

Particles + antiparticles that interact through the strong interaction.
- Interact through all 4 fundamental interactions (if charged)

Question 5

What are leptons?

Answer 5

Particles + antiparticles that don’t interact through strong interaction

Question 6

What are the basic properties of hadrons and leptons?

Answer 6

Hadrons - strong and heavy
Leptons - weak and light

Question 7

What 2 groups are hadrons split into?

Answer 7

Baryons and mesons

Question 8

What are baryons?

Answer 8

Protons and all the other hadrons that decay into protons, directly or indirectly

Question 9

What are mesons?

Answer 9

Hadrons that do not include protons in their decay products
- kaons and pions

Question 10

Are hadrons fundamental particles?

Answer 10

No their made of quarks (composite)

Question 11

Why don’t protons decay?

Answer 11

It’s stable

Question 12

What are the rules for baryon number?

Answer 12

• Total baryon number in any particles interaction never changes
• Proton and the neutron (and all other baryons) have baryon number +1
• Antibaryons have a baryon number -1
• Other particles have baryon number 0

Question 13

What are the 4 fundamental interactions?

Answer 13

• gravitational interaction
• electromagnetic interaction
• strong interaction
• weak interaction

Question 14

Which particle doesn’t decay into another?

Answer 14

Neutrino and proton

Question 15

What is a pion?

Answer 15

The pion or pi meson, is a particle which can be positively charged (pi+), negatively charged (pi-) or neutral (pi0) and has rest mass greater than a muon but less than a proton

Question 16

What do mesons do?

Answer 16

Interact with baryons via the strong force

Question 17

What is the exchange particle for the strong nuclear force?

Answer 17

Pion

Question 18

What do kaons decay into?

Answer 18

Pions

Question 19

Are leptons fundamental particles?

Answer 19

Yes

Question 20

Name the leptons

Answer 20

Electrons(e-), positron(e+), muon, antimuon, electron neutrino, electron antineutrino, muon neutrino, muon antineutrino

Question 21

What are muons?

Answer 21

Muon is a negatively charge particle with a rest mass over 200x the rest of an electron

Question 22

State the rules of lepton number

Answer 22

• lepton - lepton number +1
  (electron and muon lepton number counted separately
• antiparticle have lepton number -1
• electron and muon lepton number must be conserved

Question 23

What does a muon decay into?

Answer 23

Electron

Question 24

What are strange particles?

Answer 24

Particles that are created via the strong interaction and decay through the weak interaction

Question 25

What is a kaon?

Answer 25

Kaon or k meson; which can be positive (k+), negative (k-) or neutral (k0) and has a rest mass greater than a pion but still has less than a proton

Question 26

Why are the strange particles always created in pairs?

Answer 26

Strange particles created via strong interaction, in which strangeness is conserved - so strange particles can only be created in particle - antiparticle pairs

Question 27

What do strange particles decay by? What is significant in this?

Answer 27

Weak interaction
strangeness is not conserved (can change by +1, -1 or 0)

Question 28

What are conserved in particle interactions?

Answer 28

Energy and momentum

Question 29

What are the 4 particle numbers to think about in particle interactions?

Answer 29

Baryon number, lepton number, charge and strangeness

Question 30

What are quarks? What types of quarks are there?

Answer 30

• Fundamental particles that are building blocks of hadrons
• Up, down and strange and their antiquarks

Question 31

Why does a proton have a +1 charge?

Answer 31

Overall charge of quarks that make it up have an overall charge of +1

Question 32

What are he charges and baryon number of 3 quarks?

Answer 32

up - charge: +2/3 baryon number: +1/3
down: charge: -1/3 baryon number: +1/3
strange charge:-1/3 baryon number: +1/3

Question 33

What is the quark composition of baryons?

Answer 33

Made up of 3 quarks

Question 34

What is the quark composition of a proton and a neutron?

Answer 34

proton - uud
neutron - udd

Question 35

What is the quark composition of meson?

Answer 35

• one quark and 1 antiquark

Question 36

What is the quark composition of a pion and a kaon?

Answer 36

pion - combination of up, down, antiup and antidown quarks. pi- - du^ pi+ -ud^ and pi0 - uu^ or dd^.

kaon - addition of strange particle k- - su^ , k+ - us^ and k0 - ds^ or sd^

Question 37

What happens in terms of quark’s character in beta minus and plus decay?

Answer 37

minus - d turns into u
plus - u turns into d

Question 38

Give some characteristics of a strange particle that makes it different from a particle that is not strange

Answer 38

• Contains a strange quark
• Shorter half life than expected
• Decays via weak interaction

Question 39

Which interaction allows quark flavour/character to be changed?

Answer 39

Weak interaction