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Pair Production

Pair Production. Here a photon passes by a nucleus and converts to a particle anti particle pair. Virtual particles. A system particles that don’t have enough energy to exist are virtual. How can a particle exist without energy?

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Pair Production

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  1. Pair Production Here a photon passes by a nucleus and converts to a particle anti particle pair.

  2. Virtual particles • A system particles that don’t have enough energy to exist are virtual. • How can a particle exist without energy? • A system can be in a state of higher energy without violating a law of physics • As long as it “de-excites” to a lower state within a very small time interval. • The same relationship is true for momentum and space. • These are known as “Heisenberg’s uncertainty principles.

  3. So what if a particle “decayed into two similar mass particles?

  4. So what if a particle “decayed into two similar mass particles? • Momentum must be conserved, • So pi = pf • Also Ei = Ef • But if the new particles have mass, there could be a problem: m2 m1 m3

  5. E2=(pc)2 + (mc2) m2 p2 • If P1 = (p2 + p3) = p • E1 = (E2 + E3) ? • E12= (pc)2 + (m1c2)2 • (E2 + E3)2 = (pc)2 + ((m2 +m3)c2)2 • So E1 = (E2 + E3) if m1 = m2 + m3 • But in pair production m1 = 0 photon, and m2 and m3 have mass! m1 p1 m3 p3

  6. E2=(pc)2 + (mc2)2 m2 p2 • If P1 = (p2 + p3) = p • Let (E2 + E3)-E1 = DE • DE Dt > h/2p • So DE can be greater than zero as long as The particles exist for less time than Dt < h/(2p DE) m1 p1 m3 p3

  7. The virtual particles must recombine You would never know it happens ….unless another particle “interferes” by changing the momentum and energy of the system!

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