KEKB

KEKB, short for KEK B Factory, was a particle accelerator complex at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Ibaraki Prefecture, Japan. It operated as an asymmetric-energy electron–positron collider designed to produce large numbers of B meson pairs for studies of CP violation. The collider worked with the Belle experiment at the interaction point, providing data used to test the Standard Model.

KEKB consisted of two storage rings, one for electrons and one for positrons, colliding at the Υ(4S) resonance with a center-of-mass energy near 10.58 GeV. The electron beam energy was about 8 GeV and the positron beam energy about 3.5 GeV, a configuration chosen to yield boosted B mesons, enabling time-dependent CP violation measurements. The design emphasized high luminosity to maximize B meson production, achieving record luminosities for its era, including a peak around 2 × 10^34 cm^-2 s^-1 in the late 2000s.

During its operation, KEKB and the Belle detector produced a large body of results on B meson decays, providing crucial tests of the CKM mechanism of quark mixing and CP violation in the Standard Model. The project played a central role in establishing the B-factory approach to flavor physics and contributed to a broad program of precision measurements in the B system.

After a period of upgrades and transition to higher luminosity, KEKB was complemented and eventually superseded by the SuperKEKB accelerator, paired with the Belle II detector. The KEKB complex is remembered for its impact on flavor physics and its pioneering demonstration of high-luminosity asymmetric colliders.