image © CERN; image source
Electrons and Positrons
In the photograph above (hi-res version), each pair of spirals that originate from the same point is the track of an electron-positron pair. The positron is the antiparticle of the electron--it has the same mass as the electron, but the opposite charge. These pairs are formed when a photon--which leaves no track--changes into particles with mass. For more information about this photo, see the "antielectron (positron)" section of the "Gallery of Bubble Chamber (BC) Pictures" at CERN's Introduction to the BC Site and "Special pictures and their interpretation: Photons, electrons and positrons" at CERN's Archived Bubble Chamber Teaching Materials.
You can find more on antimatter at these CERN sites: Antimatter, Mirror of the Universe and The
History of Antimatter. To see the first observed positron track, go to the archives of From Physics Research for August 5, 2005.
Here are some interesting sites from the Physics to Go collection on elementary particle physics:
- Quarks Unbound -- Find out why particle physics is so exciting (from the Division of Particles and Fields, American Physical Society)
- The Particle Adventure -- All about particle physics (from the Lawrence Berkeley National Laboratory)
- Fermilabyrinth -- Particle physics games and puzzles (from Fermilab)