2.1.5 Classification of Particles

Question 1

What are hadrons?

Answer 1

Particles that can feel the strong nuclear force.

They are made up of smaller particles called quarks.

Question 2

What are the two types of hadrons?

Answer 2

Baryons and Mesons (classified by the amount of quarks that make them up)

Question 3

What are some baryons?

Answer 3

Nucleons (protons and neutrons) and Sigmas.

Question 4

Are baryons stable?

Answer 4

All baryons are unstable and decay into other particles apart form free protons which are the only stable ones.

All baryons end up decaying into a proton apart from protons.

Question 5

What are antibaryons?

Answer 5

The antiparticles of baryons (antiprotons, antineutrons, etc…)

However, they annihilate when they meet their pair so antibaryons are not found in normal matter.

Question 6

What is baryon number?

Answer 6

A quantum number that must be conserved (the number of baryons).

Question 7

What particles have baryon number +1?

Answer 7

Protons, neutrons and other baryons

Question 8

What particles have baryon number 0?

Answer 8

Particles that are not baryons

Question 9

What particles have baryon number -1?

Answer 9

Antibaryons

Question 10

What is neutron decay?

Answer 10

In neutron-rich conditions, neutrons decay into a proton, an electron and an antineutrino.
This is a weak interaction.

Question 11

What is a meson?

Answer 11

A type of hadron that interacts with baryons via the strong force. They are all unstable.

Question 12

What are pions?

Answer 12

The lightest mesons. They are three versions:

π+, π0 and π- (π+’s antiparticle).

Question 13

What are kaons?

Answer 13

Heavier and more unstable pions. ty have a very short lifetime and decay into pions.

Question 14

How do you detect mesons?

Answer 14

High energy particles from space called cosmic rays constantly hit the Earth interacting with the molecules in the atmosphere and producing cosmic showers including pions and kaons. this can be observed in cloud chambers.

Question 15

What are leptons?

Answer 15

Fundamental particles that do not feel the strong nuclear force.

Question 16

What are 2 examples of leptons?

Answer 16

Electrons (which are stable leptons) and muons (that are like heavy electrons and unusable)

Question 17

What interactions do neutrinos only take part in?

Answer 17

Weak interactions

Question 18

What is a lepton number?

Answer 18

A quantum number that must be conserved for muon leptons and for electron leptons.

Question 19

What are the symbol, relative charge, lepton electron and lepton muon number of each of these particles:

• electron
• electron neutrino
• muon
• muon neutrino

Answer 19

Electron:

• symbol: e-
• charge: -1
• lepton electron: +1
• lepton neutrino: 0

Electron neutrino:

• symbol: ν e
• charge: 0
• lepton electron: +1
• lepton neutrino: 0

Muon:

• symbol: μ-
• charge: -1
• lepton electron: 0
• lepton neutrino: +1

Muon neutrino:

• symbol: ν μ
• charge: 0
• lepton electron: 0
• lepton neutrino: +1

Question 20

What are strange particles?

Answer 20

Particles that have a property called strangeness.
They are created via the strong interaction. and decay through the weak interaction.
Strangeness is a quantum number that must always be conserved (in strong interactions) so they are always created in pairs.

Question 21

What do I need to remember about particle physics?

Answer 21

Appreciation that particle physics relies on the collaborative efforts of large teams of scientists and engineers to validate new knowledge.