Lecture23

Lecture23 - Physics 344 Foundations of 21st Century...

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Physics 344 Foundations of 21 st Century Physics: Relativistic and Quantum Systems Instructor: Dr. Mark Haugan Office: PHYS 282 haugan@purdue.edu TA: Dan Hartzler Office: PHYS 7 dhartzle@purdue.edu Grader: Fan Chen Office: PHYS 222 chen926@purdue.edu Office Hours: If you have questions, just email us to make an appointment. We enjoy talking about physics! Help Session: Thursdays 2:00 – 4:00 in PHYS 154 Reading: nd edition or rd edition
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The Standard Model of Particle Physics It seemed natural at this point to take a brief tour of what we understand about the structure of matter at the most fundamental level to draw together a number of situations and ideas we’d encountered before. One thing we’ve established is that the few examples of particle decays and reactions we used earlier to illustrate 4-momentum conservation are examples of a very rich class of particle phenomena. Decay processes cropped up again in the form of radioactivity as we began the study of the microscopic structure of ordinary matter and quantum mechanics that will occupy us the rest of the semester. We’ve discussed some patterns particle physicists discovered in these decay and reaction processes that led them to introduce new conserved particle properties that provide an initial explanation of the observed patterns. These properties include baryon number, lepton number, lepton and quark flavors and quark color. At a deeper level, the existence of these conserved quantities were clues regarding the fundamental interactions among leptons and quarks that drive observed particle decays and reactions.
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The properties of flavor and color actually turn out to be the analogues of charge in electrodynamics and determine how particles with flavor or color couple to the particles that mediate the Weak and Strong interactions. We wrap up our tour of the Standard Model by saying a few words about the sense in which these interactions a analogous to electrodynamics because it connects with comments we made about all fundamental interactions when we were discussing causality in relativity. The discussion will be sketchy because we don’t yet understand how even the quantum theory of electrodynamics work, but we will take a few initial steps toward remedying that immediately. We will continue our study of the quantum structure of matter and quantum mechanics by blending together what we know about Maxwell’s classical theory of electromagnetic fields and about photons into a quantum mechanics of single-photon states of the electromagnetic field.
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Quark Flavor Conservation The table at the bottom of the second hand out shows quark flavor assignments made by the Standard Model. The flavor numbers of baryons and mesons are
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Lecture23 - Physics 344 Foundations of 21st Century...

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