Particle Interactions Concept of exchange particles to explain forces between elementary particles The electromagnetic force; virtual photons as the exchange particle. The weak interaction limited β-, β+ decay, electron capture and electron-proton collisions; W+ and W- as the exchange particles. Simple Feynman diagrams to represent the above reactions or interactions in terms of particles going in and out and exchange particles.

1 Concept of exchange particles to explain forces between elementary particles.

2 Force Exchange Particle electromagnetic Photon (γ) weak interaction W+, W- Strong interaction Gluon (g)

3 The electromagnetic Interaction Possible areas of questioning Repulsion/Attraction of charged particles Annihilation Pair Creation

Simple Repulsion between like charged electrons Simple Repulsion between like charged electrons. The particle of exchange is the photon e- γ

Electromagnetic Interaction Annihilation and Pair Creation THESE PROCESSES ARE EXACT OPPOSITES OF ONE ANOTHER

Weak Interaction The weak interaction limited to β-, β+ decay, electron capture and electron-proton collisions; W+ and W- as the exchange particles.

β- decay Decay at the Quark Level udd uud

β+ decay Decay at the Quark Level W+ u udd uud

Electron Capture And Electron Proton Collisions At The Quark Level W- uud udd u e