1.4 Hadrons and Leptons

Question 1

What is a hadron?

Answer 1

Particles that feel the strong nuclear force

Question 2

What are the two types of hadrons?

Answer 2

Baryons and mesons

Question 3

Are hadrons fundamental particles?

Answer 3

No, they are made up of quarks

Question 4

What particles are baryons?

Answer 4

Protons, neutrons and others with 3 quarks

Question 5

Are baryons unstable?

Answer 5

All baryons apart from a free proton can be unstable, so all decay to become other particles. Every baryon eventually decays into a proton

Question 6

What are antibaryons?

Answer 6

The antiparticles of protons, neutrons and other baryons are antibaryons.

Question 7

Does baryon number have to be conserved?

Answer 7

Total baryon number in any particle interaction never changes

Question 8

What is the baryon number of baryons, antibaryons and other particles?

Answer 8

Baryon number is just the number of baryons:
- baryons have a baryon number of +1
- antibaryons have a baryon number of -1
- other particles have a baryon number of 0

Question 9

What type of force is beta decay caused by?

Answer 9

The weak interaction

Question 10

What is beta positive decay?

Answer 10

A proton decays into a neutron, positron and electron neutrino

Question 11

What are mesons?

Answer 11

A type of hadron with two quarks. They interact with baryons via the strong force.

Question 12

Are mesons stable?

Answer 12

All mesons are unstable

Question 13

What are the types of mesons?

Answer 13

Pions, kaons and other mesons

Question 14

What are pions?

Answer 14

• the lightest mesons
• they are the exchange particle of the strong nuclear force

Question 15

What are kaons?

Answer 15

• heavier particles than pions
• more unstable than pions
• they have a short lifetime and decay into pions

Question 16

What are cosmic ray showers?

Answer 16

High energy particles from space called cosmic rays interact with particles in the atmosphere and produce ‘showers’ of high energy particles

Question 17

How do you observe the tracks of cosmic ray showers?

Answer 17

With a cloud chamber

Question 18

How can you detect cosmic ray showers?

Answer 18

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

Question 19

What are leptons?

Answer 19

Leptons are fundamental particles which don’t feel the strong force

Question 20

What are the types of leptons?

Answer 20

Electrons, muons and taus and their neutrinos

Question 21

Which leptons are the most stable?

Answer 21

Electrons are stable leptons, muons are heavier and more unstable.

Question 22

What do muons decay into?

Answer 22

Electrons

Question 23

What type of interactions do neutrinos take part in?

Answer 23

Neutrinos only take part in the weak interaction as they have zero mass and zero electric charge.

Question 24

What is lepton number?

Answer 24

The number of leptons

Question 25

What is the lepton number of electrons, muons, taus, their neutrinos and their antiparticles?

Answer 25

- electrons, muons and taus have lepton numbers of +1 - their neutrinos have lepton numbers of +1 - positrons, antimuons and antitaus have lepton numbers of -1 - other particles have lepton numbers of 0

Question 26

What are the types of lepton number?

Answer 26

- electron lepton number (+1 for electrons and electron neutrinos) - muon lepton number (+1 for muons and muon neutrinos) - tau lepton number (+1 for taus and tau neutrinos)

Question 27

Is lepton number conserved?

Answer 27

Both baryon number and all of the types of lepton number must be conserved in all particle interactions