1.6 - HADRONS AND LEPTONS

Question 1

What particles are affected by the strong nuclear force?

Answer 1

Hadrons only

Question 2

What is the exchange particle of gravity?

Answer 2

Graviton

Question 3

What particles are affected by gravity?

Answer 3

All types

Question 4

Is particle physics concerned with gravity?

Answer 4

Not really - it is usually ignored because it is very feeble unless large masses are involved.

Question 5

What is the mass of a W boson?

Answer 5

About 100 times that of a proton.

Question 6

Compare and explain the ranges of a W boson and a photon.

Answer 6

• W boson - Very short range because it has a large mass. This means it requires a lot of energy to create and can’t travel very far.
• Photon - Infinite range because it has zero mass.

Question 7

What are hadrons?

Answer 7

Particles that feel the strong nuclear force. They are not fundamental.

Question 8

What are hadrons made of?

Answer 8

Quarks

Question 9

Are hadrons fundamental particles?

Answer 9

No, they are made of quarks.

Question 10

What are the two types of hadrons?

Answer 10

• Baryons

* Mesons

Question 11

What is the difference between baryons and mesons?

2 REASONS

Answer 11

• Baryons - Made of 3 quarks and decay into a proton directly or indirectly
• Mesons - Made of a quark and antiquark and do NOT decay into a proton

Question 12

Name some baryons.

Answer 12

• Protons
• Neutrons
• Other particles (e.g. Sigmas)

Question 13

What is the only stable baryon?

Answer 13

Proton - this means all baryons will decay in sequence and eventually form a proton.

Question 14

Are antibaryons found in ordinary matter?

Answer 14

No, because they annihilate with baryons.

Question 15

What values are particles given in baryon number conservation?

Answer 15

• Baryons = +1
• Antibaryons = -1
• Other particles = 0

Question 16

What are some examples of antibaryons?

Answer 16

• Antiprotons

* Antineutrons

Question 17

Why does beta decay happen?

Answer 17

Neutrons are not stable baryons, but protons are, so a neutron will decay into a proton.

Question 18

Are mesons stable?

Answer 18

No

Question 19

What are the different types of meson?

Answer 19

Pions and kaons

Question 20

What is another name for a pion?

Answer 20

Pi-meson

Question 21

What is another name for a kaon?

Answer 21

K-meson

Question 22

What is the difference between pions and kaons?

Answer 22

• Pions - Lighter, less unstable, not strange

* Kaons - Heavier, more unstable, strange, very short lifetime

Question 23

What is the antiparticle for π+

Answer 23

π-

Question 24

What is the antiparticle for π0

Answer 24

Itself

Question 25

What happens to kaons?

Answer 25

They decay into pions.

Question 26

Where were pions and kaons seen?

Answer 26

Cosmic rays interact with molecules in the atmosphere and produce "showers" of lots of high-energy particles, including pions and kaons. = cosmic ray showers

Question 27

How did scientists find pions and kaons? How are they seen now?

Answer 27

Cloud chamber used to observe the tracks of the particles. Now: Two Geiger counters on top of each other with absorbing lead between them. If both counters detect radiation simultaneously it is likely to be a particle from a cosmic ray shower (rather than just random noise like background radiation)

Question 28

How do mesons interact with baryons?

Answer 28

Through the strong force.

Question 29

What are the general rules for determining the type of interaction in a reaction?

Answer 29

* If any leptons involved at all -> Weak interaction * If strangeness isn't conserved -> Weak interaction * All others -> Strong interaction

Question 30

What are leptons?

Answer 30

Particles that do not feel the strong interaction. They are fundamental.

Question 31

What are the different leptons?

Answer 31

* Electrons * Muons * Neutrinos * Tau

Question 32

What happens to muons?

Answer 32

The eventually decay into electrons. This is because muons are unstable.

Question 33

What can muons be described as?

Answer 33

Heavy electrons.

Question 34

What is the mass and charge of neutrinos?

Answer 34

* Mass - Almost zero | * Charge - Zero

Question 35

How does lepton conservation work?

Answer 35

* There are 3 generations of lepton number - electron, muon and tau * Each lepton number must be conserved separately * Each normal lepton and its respective neutrino is given a lepton number of +1 * Each anti-lepton and its respective antineutrino is given a lepton number of -1

Question 36

What are the symbols for each lepton number?

Answer 36

* Electron lepton number = Le * Muon lepton number = Lmuon * Tau lepton number = Lt

Question 37

What are antiparticles of hadrons made from?

Answer 37

Antiquarks

Question 38

How do strange particles (e.g. kaons) interact?

Answer 38

* Created by the strong interaction | * Decay via the weak interaction

Question 39

Strange particles are always produced in pairs (e.g. K+ and K-). Why?

Answer 39

The strangeness cancels out to become 0, so that strangeness is conserved. Therefore, the reaction is a strong interaction.

Question 40

What are the types of quark?

Answer 40

* Up * Down * Strange

Question 41

What is the charge of an up quark?

Answer 41

+2/3

Question 42

What is the charge of a down quark?

Answer 42

-1/3

Question 43

What is the charge of a strange quark?

Answer 43

-1/3

Question 44

What is the charge of an anti-up antiquark?

Answer 44

-2/3

Question 45

What is the charge of an anti-down antiquark?

Answer 45

+1/3

Question 46

What is the charge of an anti-strange antiquark?

Answer 46

+1/3

Question 47

What is the strangeness of a strange quark?

Answer 47

-1

Question 48

What is the strangeness of an anti-strange antiquark?

Answer 48

+1

Question 49

What is unusual about strangeness?

Answer 49

* It is not ALWAYS conserved * Strange quarks are given a strangeness of -1 and anti-strange antiquarks are given a strangeness of +1. In weak force: it is not usually conserved and can change by +1, -1, or 0

Question 50

What quarks make up a proton?

Answer 50

uud

Question 51

What quarks make up an antiproton?

Answer 51

anti-u, anti-u, anti-d

Question 52

What quarks make up a neutron?

Answer 52

udd

Question 53

What quarks make up an antineutron?

Answer 53

anti-u, anti-d, anti-d

Question 54

What are baryons made of?

Answer 54

3 quarks

Question 55

What are mesons made of?

Answer 55

A quark and an antiquark

Question 56

What is the antiparticle of a pi-plus meson?

Answer 56

A pi-minus meson.

Question 57

Remember to revise the diagram on mesons.

Answer 57

Pg 14 of the revision guide

Question 58

What is a weak interaction in terms of quarks?

Answer 58

A weak interaction is something that changes the quark type (e.g. A neutron (udd) turning into a proton (uud))

Question 59

What properties are conserved in an interaction?

Answer 59

* Charge * Baryon number * Strangeness (only in strong interactions) * Lepton number (all 3 generations separately)

Question 60

How is baryon number conserved in pair production?

Answer 60

Question 61

How is charge conserved in pair production and neutron decay (e.g. beta minus)?

Answer 61

Question 62

Why is strangeness only conserved in strong interaction?

Answer 62

You can change the type of quark in weak interactions. | In strong interactions the strange quarks have to be conserved throughout.

Question 63

Can a quark exist on its own?

Answer 63

No.

Question 64

What is quark confinement?

Answer 64

The idea that quarks cannot exist not their own.

Question 65

Through which interaction do hadrons tend to decay?

Answer 65

Weak

Question 66

Describe the mass, range and charge of a W boson.

Answer 66

* Non-zero rest mass * 0.001fm range * Can be positively or negatively charged

Question 67

What are the quarks in a K0 meson?

Answer 67

* Anti-s | * d

Question 68

What are the quarks in an anti-K0 meson?

Answer 68

* s | * Anti-d