BRAINCAKEAnnihilation
When a particle meets its antiparticle, they annihilate: their mass is converted completely into energy, usually in the form of photons. For an electron and a positron:
e- + e+ → γ + γ
Two photons are produced, not one. If the particles are at rest, their total momentum is zero, so the photons must move off in opposite directions with equal energies, so that momentum is conserved. A single photon always carries momentum, so it could not be the only product.
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Key terms in this lesson
- lepton number
- A quantum number assigned +1 to leptons, -1 to antileptons and 0 to other particles, conserved in every interaction.
More in Particle Physics
- Relativistic Energies and GeV
- Mass in MeV/c2
- Particles and Antiparticles
- Pair Production
- The Standard Model
- Quarks
- Leptons
- Baryons and Mesons
All 19 lessons in Particle Physics · All Edexcel A-level Physics topics