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Quarks And Leptons Notes

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Unit 1: 2 Quarks and leptons

CLASSIFICATION OF PARTICLES HADRONS

LEPTONS

Any particle experiencing the strong nuclear force

React by the weak interaction (& electromagnetic if charged)

Baryons

Made up of three quarks

Mesons

A quark-antiquark pair

-decay into protons (directly -do not include protons or indirectly) in their decay products

Protons (1919) Particle Antiparticle

Neutrons (1932)

p

Pion πmeson (1947)

Kaon Kmeson (1948)

n

(1955)

(1955)

Electron (1897)

Muon (1937)

Electron neutrino (1957)

Muon neutrino (1961)

(β-) Self

(β+) (positron) (1932)

Particles, antiparticles & neutrinos Antiparticles have:

• Identical mass

• Identical lifetime, if unstable

• Opposite in all other properties e.g. charge, spin etc. When a particle and and an anti-particle meet they annihilate each other. (pair annihilation)

LEPTONS NEUTRINO TYPES: Neutrino, γ created in a β+ (positron) emission (beta decay) and explains the range of energies and directions of the emitted positrons. This occurs when a proton changes into a neutron p ! n + β+ +
Properties

• Zero charge

• Near zero mass (1/2000 mass of electron)

• Velocity = speed of light (Possible if has zero mass)

• Virtually no interaction with matter (very hard to detect)

• Interact by means of the weak interaction (see later)

• Spin = ½ (allows classification as a fermion, if spin is 1,2,3 etc it is a boson) Antineutrino - created in a β- emission (electron) n !p + β- +

PHYSICS AS NOTES

5

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