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Unformatted text preview: 253a/Schwartz Due November 9, 2010 Problem Set 9 1. Consider the following diagram for e + e- → μ + μ- in QED a) What other diagrams contribute at the same order in perturbation theory? b) Show explicitly that the sum of this diagram and the diagram with the photons crossed is gauge invariant (independent of ξ ). 2. Parity Violation. We calculated that e + e- → μ + μ- has a 1 + cos 2 θ angular dependence. This agrees with experiment, as the simulated data in Figure 1 shows. However, the angular distribu- tion for scattering into muon neutrinos e + e- → ν μ ν ¯ μ is very different, as shown in the simulated data in Figure 2. (This simulation is somewhat idealized – interference has been dropped, but the physics is correct and has been observed.) Minus 1.0 Minus 0.5 0.0 0.5 1.0 100 200 300 400 500 600 cos Θ events Figure 1. e + e- → μ + μ- Minus 1.0 Minus 0.5 0.0 0.5 1.0 100 200 300 400 500 600 cos Θ events Figure 2. e + e- → ν μ ν ¯ μ a) At low energy, the total cross section σ tot for e + e- → ν μ ν ¯ μ scattering grows with...
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This note was uploaded on 02/04/2012 for the course PHYS 253A at Harvard.