KEKB (accelerator)

KEKB is the name of a particle accelerator used in the Belle experiment to study CP violation. It is called a B-factory for its copious production of B-mesons which provide a golden mode to study and measure the CP violation due to its property of decaying into other lighter mesons. KEKB is basically an asymmetric electron–positron collider, with electrons having the energy of 8 GeV and positrons having the energy of 3.5 GeV, giving 10.58 GeV centre-of-mass energy, which is equal to the mass of Upsilon(4S).

There are basically two rings for accelerating electrons and positrons. The ring for electrons, having energy of 8 GeV, is called the high-energy ring (HER), while the ring for positrons, having energy of 3.5 GeV, is called low-energy ring (LER). The HER and LER are constructed side-by-side in the tunnel, which has been excavated already in the past for the former TRISTAN accelerator. (TRISTAN was the first site to confirm vacuum polarization around an electron.) [cite journal
last=Levine | first=I. | coauthors=TOPAZ Collaboration
title=Measurement of the Electromagnetic Coupling at Large Momentum Transfer
journal=Physical Review Letters | year=1997
volume=78 | pages=424–427
doi=10.1103/PhysRevLett.78.424 ] The circumference of each ring is 3016 m, having four straight sections. In the KEKB, there is only one interaction point in the ""Tsukuba area"", where the Belle experiment is located. The other areas (called "Fuju", "Nikko" and "Oho") are currently not actively used by an experiment.

The KEKB accelerator is located at the "High Energy Accelerator Research Organisation (KEK)" in Tsukuba, Ibaraki Prefecture, Japan.

Since the energy of the electrons and positrons is asymmetric, the B meson pairs are created with a Lorentz boost factor of 0.425.

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