Phy107Lect36_6per

Phy107Lect36_6per - From Last Time. Discussed quarks and...

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1 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. Wed. Dec 8 Phy107 Lecture 36 Today • The weak interaction • Neutrinos • Quark decay • Detecting quarks and the W, Z bosons Wed. Dec 8 Phy107 Lecture 36 The Weak Force EM STRONG WEAK 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” 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 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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2 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. 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 Wed. Dec 8 Phy107 Lecture 36 • Interaction range determined by particle mass.
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Phy107Lect36_6per - From Last Time. Discussed quarks and...

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