BaBar particle detector. Wide angle view of engineers working on the open BaBar particle detector at the Stanford Linear Accelerator Center (SLAC), California, USA. It is hoped that BaBar will help to explain why there is more matter than antimatter in the universe. BaBar will detect the B mesons and their antimatter equivalents, anti-B mesons, that result from the collisions of accelerated electrons and positrons. The collisions will occur at the detector's centre. Different B meson and anti-B meson decay rates would help to explain the greater amount of matter in the universe. When BaBar is in use the large iron doors at far left and right are closed.