Belle is an international collaborative experiment at the KEKB B-factory at Tsukuba, Japan, which took data from 1999 to 2010. Two Australian groups are members of the Belle Collaboration, our own group here in Sydney, and a groups at the University of Melbourne (the EPP group).
The primary purpose of Belle was to investigate small differences between the decay properties of particles and antiparticles, in order to try to shed some light on the imbalance between matter and anti-matter in the universe, and also to improve our understanding of these interactions.
Belle's work is carried out by studying the decays of B-mesons resulting from the collision of electrons and positrons at the KEKB B-factory. B-mesons are very short-lived - they normally decay within 2 trillionths of a second - but the mesons produced at the KEK B-factory still travel a few tenths of a millimetre before decaying, far enough to be measured using modern silicon vertex detectors. These studies have furnished proof for CP-violation in the B-meson system, in addition to the CP-violation in the K-meson system which has been known about since the 1960s. This is a significant addition to our understanding of particle physics, which is summarised in the Standard Model.
Below is shown an early interaction in the Belle detector.