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 behavior 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, usually HERA-B is not considered a B-factory. Two B-factories were designed and built in the 1990s, and they operated from late 1999 onward: the Belle experiment at the KEKBcollider in Tsukuba, Japan, and the BaBar experiment at the PEP-II collider at SLAC in California, United States. They were both electron-positron colliders with the center of mass energy tuned to the ϒ resonance peak, which is just above the threshold for decay into two B mesons. BaBar prematurely ceased data collection in 2008 due to budget cuts, but Belle ran until 2010, when it stopped data collection both because it had reached its intended integrated luminosity and because construction was to begin on upgrades to the experiment.
Current experiments
Three "next generation" B-factories were to be built in the 2010s and 2020s: SuperB near Rome in Italy; Belle II, an upgrade to Belle, and SuperPEP-II, an upgrade to the PEP-II accelerator. SuperB was canceled, and the proposal for SuperPEP-II was never acted upon. However, Belle II successfully started taking data in 2018 and is currently the only next-generation B-factory in operation. In addition to Belle II there is the LHCb-experiment at the LHC, which started operations in 2010 and studies primarily the physics of bottom-quark containing hadrons, and thus could be understood to be a B-factory of this "next generation." But LHCb is not usually referred to as a B-factory as the experiment and the corresponding collider are not used solely for the study of b-quark particles but have other purposes beside b-quark physics.
