Phy107Lect35

Phy107Lect35 - From Last Time Particles are quanta of a quantum field The vacuum is not empty Uncertainty principle says particles can

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Mon. Dec 6 Phy107 Lecture 35 From Last Time… • Particles are quanta of a quantum field • The vacuum is not ‘empty’ – Uncertainty principle says particles can spontaneously appear for short times • Antiparticles • Matter is made of leptons and quarks • Three ‘generations’ of leptons/quarks • Forces are due to exchange of bosons
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Mon. Dec 6 Phy107 Lecture 35 Today • Generations of leptons and quarks • Composite particles: Hadrons, Baryons, and mesons (made of quarks) • Electrons and neutrinos • More strong and weak interactions – Gluons, W and Z particles
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Mon. Dec 6 Phy107 Lecture 35 Three generations of particles Light Heavier Heaviest
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Mon. Dec 6 Phy107 Lecture 35 Quarks Light (Gen. I) Heavy (Gen. II) Heaviest (Gen. III) Quarks ‘paired’ in generations same way as electron and neutrino
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Mon. Dec 6 Phy107 Lecture 35 Heavy, Heavier, Heaviest 6 different kinds of quarks. Matter is composed mainly of up quarks and down quarks bound in the nuclei of atoms . Masses vary dramatically (from ~0.005 to 175 [GeV/ c 2 ]) Heavier quarks are unstable, rapidly decay to lighter quarks up down strange charm bottom top 0.001 0.01 0.1 1 10 100 1000 0 1 2 3 4 5 6 7 Mass [ GeV /c 2 ] Gold atom Silver atom Proton Example: t b (~10 -23 [s]) b c (~10 -12 [s]) c s (~10 -12 [s]) s u (~10 -7- 10 -10 [s]) More on quark decays later…
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Mon. Dec 6 Phy107 Lecture 35 Protons/Neutrons are composite
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Mon. Dec 6 Phy107 Lecture 35 Hadrons / Baryons • The forces which hold the protons and neutrons together in the nucleus are VERY strong . •They interact via the STRONG FORCE . • Protons and neutrons are among a class of particles called “hadrons ( Greek for strong ). • Hadrons interact very strongly with other hadrons! Baryons are hadrons which contain 3 quarks (no anti-quarks). Anti-baryons are hadrons which contain 3 anti-quarks (no quarks ).
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Mon. Dec 6 Phy107 Lecture 35 Protons & Neutrons To make a proton: We bind 2 up quarks of Q = +2/3 and 1 down quark of Q = -1/3 . The total charge is 2/3 + 2/3 + (-1/3) = +1 ! To make a neutron: We bind 2 down quarks of Q= -1/3 with 1 up quark of Q = +2/3 to get: (-1/3) + (-1/3) + (2/3) = 0 !
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Mon. Dec 6 Phy107 Lecture 35 Are there baryons other than protons and neutrons? Other quarks can combine to form other baryons. For example : u s d This combination is called a Lambda baryon, or Λ 0 for short (What is the charge of this object?) u This combination is called a Delta baryon, or Δ ++ for short What’s this one’s charge?
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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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Phy107Lect35 - From Last Time Particles are quanta of a quantum field The vacuum is not empty Uncertainty principle says particles can

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