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Quarks And Leptons Notes

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Unit 1: 2 Quarks and leptons



Any particle experiencing the strong nuclear force

React by the weak interaction (& electromagnetic if charged)


Made up of three quarks


A quark-antiquark pair

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

Protons (1919) Particle Antiparticle

Neutrons (1932)


Pion πmeson (1947)

Kaon Kmeson (1948)




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+ +

• 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- +



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