In particle physics, a B-factory, or sometimes a beauty factory,[1] is a collider-based scientific machine designed to produce a large number (of the order of 109) of B mesons and analyze their properties. Tauons and D mesons are also copiously produced at B-factories, which allows precise studies of their properties.

Two B-factories were designed and built in the 1990s. 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.[2]

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|, and measurements of purely leptonic B meson decays.

Proposals for next-generation B-factories include the canceled SuperB designed to be built in Frascati near Rome in Italy, and Belle II in Japan.

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