Phy107Lect39_6per

# Phy107Lect39_6per - Final Exam Sat Dec 18 2:45-4:45 pm 1300...

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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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