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Phy107Lect36 - From Last Time Discussed quarks and their...

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Wed. Dec 8 Phy107 Lecture 36 From Last Time… Discussed quarks and their interactions Six generation, 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.
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Wed. Dec 8 Phy107 Lecture 36 Today The weak interaction • Neutrinos Quark decay Detecting quarks and the W, Z bosons
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Wed. Dec 8 Phy107 Lecture 36 The Weak Force EM STRONG WEAK
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Wed. Dec 8 Phy107 Lecture 36 Carriers of the weak force Like the Electromagnetic & Strong forces, the Weak force is also mediated by “force carriers”. For the weak force, there are three force carriers: W + W - Z 0 These “weak force” carriers carry electric charge also ! This “weak force” carrier is electrically neutral The “charge” of the weak interaction is called “weak charge”
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Wed. Dec 8 Phy107 Lecture 36 Massive particles The W + , W - , and Z o are very massive W + W - Z o 80.4 Mev/c 2 91.2 Mev/c 2 Top quark is heaviest fundamental particle. W, Z have ~ half the mass of the top quark
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Wed. Dec 8 Phy107 Lecture 36 What interacts? Any particle with a ‘weak charge’ will interact via the weak interaction. All quarks and leptons carry a weak charge. The weak interaction occurs by exchanging a W + , W - , or Z o But all quarks have electric charge, and half the leptons do. In this case, weak interaction overwhelmed by electromagnetic interaction.
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Wed. Dec 8 Phy107 Lecture 36 Exchanging the Z o Both of these contribute to the total interaction between electrons • Z o is uncharged particle like the photon, but has mass. But the electromagnetic interaction is much larger. Neutral weak int. Electromagnetic int. • Zero charge • Mass ~ 90 GeV / c 2 • Range ~ 10 -18 m • Zero charge • Mass = 0 GeV / c 2 • Range ~ inf.
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Wed. Dec 8 Phy107 Lecture 36 Range of the interaction Electron doesn’t have enough energy to create Z o. • Z o only present due to uncertainty relation (Energy uncertainty)x(Time uncertainty)~Planck cnst It can only exist for a time determined by Time uncertainty ~ Planck cnst Particle mass Farthest it can travel in that time is Range~(Light Speed)x Planck cnst Particle Mass ~ 10 -18 m
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Wed. Dec 8 Phy107 Lecture 36 Interaction range determined by particle mass.
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