ismchapter13edition4 - Chapter 13 ! Particle Physics 13-1....

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301 Chapter 13 ! Particle Physics 13-1. (a) Because the two pions are initially at rest, the net momentum of the system is zero, both before and after annihilation. For the momentum of the system to be zero after the interaction, the momenta of the two photons must be equal in magnitude and opposite in direction, i.e., their momentum vectors must add to zero. Because the photon energy is , their energies are also equal. (b) The energy of each photon equals the rest energy of a B + or a B ! . (c) 13-2. (a) (b) (c) 13-3. (a) n p (b) p n (c) p p B 0 B ! B 0 n p n p p p 13-4. (a) assuming no neutrino (electron’s mass is included in that of 32 S) To a good approximation, the electron has all of the kinetic energy (b) In the absence of a neutrino, the 32 S and the electron have equal and opposite momenta.
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Chapter 13 ! Particle Physics 302 (Problem 13-4 continued) The momentum of the electron is given by: The kinetic energy of the 32 S is then: (c) As noted above, the momenta of the electron and 32 S are equal in magnitude and opposite in direction. 13-5. (a) A single photon cannot conserve both energy and momentum. (b) To conserve momentum each photon must have equal and opposite momenta so that the total momentum is zero. Thus, they have equal energies, each equal to the rest energy of a proton: (c) (d)
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Chapter 13 ! Particle Physics 303 13-6. (a) Conservation of charge: . Conservation of charge is violated, so the reaction is forbidden. (b) Conservation of charge: . Conservation of charge is violated, so the reaction is forbidden. 13-7 From Table 13-6: (a) 7 (1670) 30 MeV (b) E (2030) 175MeV (c) ) (1232) 120 MeV 13-8. (a) Weak interaction (b) Electromagnetic interaction (c) Strong interaction (d) Weak interaction 13-9. is caused by the electromagnetic interaction; is caused by the weak interaction. The electromagnetic interaction is the faster and stronger, so the B 0 will decay more quickly; the B ! will live longer. 13-10. (a) Electromagnetic interaction (b) Weak interaction (c) Electromagnetic interaction (d) Weak interaction (e) Strong interaction (f) Weak interaction 13-11. For neutrino mass m = 0, travel time to Earth is ,where . For neutrinos with mass , where .
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Chapter 13 ! Particle Physics 304 (Problem 13-11 continued) Substituting into , 13-12. The E + and E ! are members of an isospin multiplet, two charge states of the E hadron. Their mass difference is due to electromagnetic effects. The B + and B ! are a particle-antiparticle pair.
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Chapter 13 ! Particle Physics 305 13-13. (a) < : < e : !
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This note was uploaded on 10/05/2009 for the course PHYSICS 7C taught by Professor Lin during the Spring '08 term at University of California, Berkeley.

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ismchapter13edition4 - Chapter 13 ! Particle Physics 13-1....

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