QCEphysics

Particle interactions

define the concept of lepton number and baryon number

recall the conservation of lepton number and baryon number in particle interaction

- The conservation of baryon number and conservation of lepton number states that in any interaction, the number is conserved.

explain the following interactions of particles using Feynman diagrams

- electron and electron
- electron and positron
- a neutron decaying into a proton

Electron and electron

- As an electron approaches another electron, they move closer. The electrostatic repulsion between them gets stronger and stronger until they exchange a photon (electromagnetic force carrier), which pushes each electron away from each other.

Electron and positron

- Bhabha scattering

• "Time reversed" arrow for positron, however it is approaching electron as the lines get closer. At the moment of interaction, they exchange a virtual photon and scatter off each other with velocities changed.

- Annihilation

• The electron and positron approach each other. Rather than scattering, they annihilate each other, forming a photon. The photon's energy creates a new electron-positron pair. This is the same way the energy from the Big-Bang was converted to particle-antiparticle pairs.

Neutron decaying into a proton