In particle physics, a B-factory, or sometimes a beauty factory, is a particle collider experiment designed to produce and detect a large number of B mesons so that their properties and behaviour can be measured with small statistical uncertainty. Tauons and D mesons are also copiously produced at B-factories.
A sort of "prototype" or "precursor" B-factory was the HERA-B experiment at DESY that studied B-meson physics in the 1990s-2000s before the actual B-factories were constructed/operational. However, uually HERA-B is not considered a B-factory.
Two B-factories were designed and built in the 1990s, and they operated from late 1999 onwards. They are both based on electron-positron colliders with the centre of mass energy tuned to the ϒ(4S) resonance peak, which is just above the threshold for decay into two B mesons (both experiments took smaller data samples at different centre of mass energies). The Belle experiment at the KEKB collider in Tsukuba, Japan, and the BaBar experiment at the PEP-II collider at SLAC laboratory in California, United States, completed data collection in 2010 and 2008, respectively.
The B-factories yielded a rich harvest of results, including the first observation of CP violation outside of the kaon system, measurements of the CKM parameters |Vub| and |Vcb|, measurements of purely leptonic B meson decays and searches for new Physics.
Next-generation B-factories, to be built in the 2010s and 2020s, are the subsequently canceled SuperB that was designed to be built in Frascati near Rome in Italy, and Belle II, an upgrade to Belle, which began operations in 2018. In addition to these there is the LHCb-experiment at the LHC, which started operations in 2010 and is active as of 2019 and studies primarily the physics of bottom-quark containing hadrons, and thus could be understood to be a B-factory of this "next generation" (generation of 2010s and 2020s). But LHCb is not usually referred to as a B-factory as the experiment and (perhaps more importantly) the corresponding collider (that is, the LHC) are not used solely for the study of b-quark particles but have other purposes beside b-quark physics.
- J.T. Volk; et al. (1987). "Letter of Intent for a Tevatron Beauty Factory" (PDF). Fermilab Proposal #783.