Phy107Lect39_6per - Final Exam: Sat. Dec. 18, 2:45-4:45 pm,...

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1 Wed. Dec 15 Phy107 Lecture 39 Review Chap. 18: Particle Physics • Particles and fields: a new picture • Quarks and leptons: the particle zoo • The weak interaction • Unification and mass • The approach of string theory Final Exam : Sat. Dec. 18, 2:45-4:45 pm, 1300 Sterling Exam is cumulative, covering all material Wed. Dec 15 Phy107 Lecture 39 Particle physics • Have talked about several particles – Electron, photon, proton, neutron, quark • There are a plethora of others that we haven’t talked about. • Most of these are composite, meaning that they have internal constituents. • Just as an atom is not ‘fundamental’, but has internal constituents electron, proton, neutron. Wed. Dec 15 Phy107 Lecture 39 Pair production, annihilation • Every fermion has an anti-particle Exactly same mass, but opposite charge • Particle and anti-particle can ‘annihilate’ to form two photons. • Photon can ‘disappear’ to form electron-positron pair. Wed. Dec 15 Phy107 Lecture 39 Particles and fields • What are particles? • We say that particles are quanta of a corresponding field. • But what does this mean? • Think about photons. – One photon means the electromagnetic field has (Planck’s const)x(frequency) = h f of energy. – Two photons means 2h f of energy. – Three photons means 3h f of energy. Wed. Dec 15 Phy107 Lecture 39 Energy uncertainty • To make a very short pulse in time, need to combine a range of frequencies. • Frequency related to quantum energy by E =h f . • Heisenberg uncertainty relation can also be stated (Energy uncertainty)x(time uncertainty) ~ (Planck’s constant) In other words, if a particle of energy E only exists for a time less than h / E, it doesn’t require any energy to create it! Wed. Dec 15 Phy107 Lecture 39 The vacuum • Modern particle physics says that the vacuum is not as simple as one might think. • The vacuum is continually ‘fluctuating’, with virtual photons, electron-positron pairs, etc. • Vacuum is really empty at all.
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2 Wed. Dec 15 Phy107 Lecture 39 What are these particles? • Broadly divided into – Matter particles (Leptons and quarks) – Force particles (Photon, W, Z, gluons) • In the standard model, these particles are quite different • Leptons and quarks make up matter • Other particles are responsible for the fundamental forces. Wed. Dec 15 Phy107 Lecture 39 The Matter Particles • “ Matter is made of atoms “ Leptons e ν e Quarks d u “ Atoms are made of leptons and quarks “ “Atoms are made of leptons and quarks” Wed. Dec 15 Phy107 Lecture 39 The particle garden • Particle physics at this point has settled on a countable number of ‘fundamental particles’. • The bad news: – There are (6 leptons +6 quarks)+ (4 electroweak bosons +8 gluons +1 graviton) =25 fundamental particles, not counting antiparticles!
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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 University of Wisconsin.

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Phy107Lect39_6per - Final Exam: Sat. Dec. 18, 2:45-4:45 pm,...

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