Phy107Spr06Lect37

Phy107Spr06Lect37 - From Last Time The Standard Model D isc...

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1 Wed. Apr. 26, 2006 Phy107 Lect. 36 1 From Last Time… • Discussed quarks and their interactions • Six quarks, paired in three generations • Quarks have electric charge, participate in EM interaction by exchanging photons. • Quarks also have color charge, participate in color interaction by exchanging gluons. • Color charge as six varieties Red, green, blue, anti-red, anti-green, anti-blue Like colors repel, unlike colors attract. Wed. Apr. 26, 2006 Phy107 Lect. 36 2 The Standard Model • 6 leptons • 6 quarks • 4 interactions – Electromagnetic, Gravitational, Strong, Weak – ‘mediated’ by 13 exchange bosons, which are excitations of the corresponding fields. Wed. Apr. 26, 2006 Phy107 Lect. 36 3 Leptons • The cats have an electrical charge of - e • The fleas (neutrinos) have zero charge (neutral). Wed. Apr. 26, 2006 Phy107 Lect. 36 4 Lepton generations • Each electron-like particle and neutrino paired in a generation. e ν e μ ν μ τ ν τ Generation I Generation II Generation III Wed. Apr. 26, 2006 Phy107 Lect. 36 5 Question The difference between the different generations of leptons is A. their charge B. their mass C. their color D. their spin Wed. Apr. 26, 2006 Phy107 Lect. 36 6 EM interaction • Charged particles interact via the electromagnetic (EM) interaction – A charged particle couples to the photon field – It excites a photon (excited state of photon field) and loses energy. – Another charged particle can absorb the energy from the photon field (photon disappears). Only particles with an electric charge couple to the photon field.
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2 Wed. Apr. 26, 2006 Phy107 Lect. 36 7 Quarks Six different kind of quarks, analogous to the six leptons All quarks have an electric charge, they couple to photon field. But they also have a ‘color’ charge, and they couple to the gluon field. This is the ‘strong’ interaction Wed. Apr. 26, 2006 Phy107 Lect. 36 8 Quark generations • Six different quarks, but two per generation – Just like the leptons u d Generation I c s Generation II t b Generation III Charge +2/3 -1/3 Wed. Apr. 26, 2006 Phy107 Lect. 36 9 Four interactions • The four fundamental interactions all have associated fields and mediating particles. • Talked about – EM interaction between electrically charged particles by exchange of photons – Strong interaction between ‘color’ charged particles by gluon exchange Wed. Apr. 26, 2006 Phy107 Lect. 36 10 The weak interaction • Weak interaction is ‘not strong’, but is important. It can change one particle into another! • Muon, tau, can turn into neutrinos! • Quarks can turn into other quarks • Particles with a ‘weak charge’ couple to the ‘weak field’ • Excitations of the weak field are the Z and W bosons. Wed. Apr. 26, 2006 Phy107 Lect. 36 11 • "Although the weak interaction is much weaker than both the strong and the electromagnetic interactions, it is of great importance in many connections. The actual strength of the weak interaction is also of significance. The energy of the sun, all-important for life on earth, is produced when hydrogen fuses or burns into helium in a chain
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This note was uploaded on 01/05/2012 for the course PHYS 107 taught by Professor N/a during the Spring '08 term at Wisconsin.

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Phy107Spr06Lect37 - From Last Time The Standard Model D isc...

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