Lecture22 - 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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Particle Decays and Conservation Laws As the examples we considered last time suggest, particles decay spontaneously into other particles unless some conservation law prevents them from doing so. This paraphrases the rule of thumb we mentioned earlier. Patterns in the data on particle lifetimes and decay products of the kind we sampled last time led to the identification of laws for the conservation of several new particle properties that play roles in the Standard Model and in the theories of its three fundamental interactions. For completeness, we will list conservation laws familiar from previous work as well as the new Standard Model ones.
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4-Momentum Conservation This applies to all physical processes and, in the case of particle decays, imposes the obvious constraint that none of the decay products of an unstable particle can be more massive than the particle itself. We generally analyze decays in the rest frame of the unstable particle, in which case the system’s initial momentum is zero and its energy is the particle’s rest mass. Assuming that nothing else in the Universe interacts significantly with the initial unstable particle or with its decay products, the momentum of the system consisting of the decay products must be zero and its mass, which includes any kinetic energy they possess, must be equal to the mass of the initial unstable
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This note was uploaded on 12/09/2011 for the course PHYS 344 taught by Professor Garfinkel during the Fall '08 term at Purdue University-West Lafayette.

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Lecture22 - Physics 344 Foundations of 21st Century...

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