KEKB ( KEK B -factory ) was operated from 1998 to 2010 particle accelerator complex at KEK in Tsukuba Japanese research center, which was optimized for the production of B- mesons. These then in two separate storage rings with 3 -kilometers long in bunches ( bunches ) were accelerated to energies of 8 and 3.5 GeV with a linear accelerator electrons and positrons, and summarized in the Belle detector - crosses with two rings - specifically to brought collision. Due to the different energies of the electrons and positrons at the collision point, there was an asymmetric B- factory. Accelerator and detector were specially designed for the observation of CP violation in the decay of B mesons.
In the late 1980s were taken for the conversion of the existing particle accelerator at KEK TRISTAN ( 1986-1995 ), which were approved by the CEC in 1993, under the condition of maximum utilization of the existing infrastructure and technology of TRISTAN planning. Construction began in 1994 and 1998 was the KEKB and 1999, the Belle detector will be put into operation. The goal was the production of B- mesons and the observation of CP violation in the decay. To this end, in contrast to the previous project TRISTAN was a 200 - to 300 -fold higher required luminosity. KEKB was designed as a B- factory with asymmetric energies, for which two separate storage rings for electrons (8 GeV ) and positrons ( 3.5 GeV ) were built in the existing 3 km long tunnel of TRISTAN. Furthermore, an upgrade and extension of the former linear accelerator was necessary because at its maximum energy should be fed into the storage rings, the particles already; who was then serving as a pre TRISTAN Accumulation Ring was no longer needed.
After over ten years of successful operation, which culminated in the Nobel Prize for Physics in 2008 for Makoto Kobayashi and Toshihide Maskawa, the operation of the KEK B- factory in June 2010 has been set. As subsequent accelerator at KEK of SuperKEKB under construction, with the follow-up experiment Belle II; completion is scheduled for 2014.
Construction and operation
With the linear accelerator ( LINAC ), the electrons and positrons accelerated to its maximum energy of 8 and 3.5 and is fed to the high energy ring ( HER), respectively, in the 8 GeV Low Energy ring ( LER ) 3.5 GeV. The two separate storage rings have a circumference of 3016 meters and cross at the point of interaction ( Interaction Point) Belle Detekter (or later in the Belle II detector ) in the experimental hall Tsukuba. In the opposite experiment hall Fuji exchange rings at different heights its horizontal position, without the particles collide with each other. The linear accelerator was built for space reasons in the form of a J, and the electrons are deflected at an energy of from 1.7 GeV to 180 °. The positrons were produced by bombarding a 14 mm thick water-cooled tantalum plate with 3.7- GeV electrons in the under part of the LINAC and both types of particles accelerated to their final energies then in the main part of the linac. The LINAC had a total length of approximately 600 meters and was 200 meters longer than its predecessor ( TRISTAN ).
The target luminosity of 1034 cm -2 s- 1 was reached in 2003. Since crossing the bunches in the Belle detector at an angle of 22 mrad, while the Teilchpakete penetrate at point of interaction only partially, which limits the achievable rate of particle collisions. Through the installation of crab cavities in 2007, slightly rotate the respective bunches before the collision, could be achieved better penetration and increased to June 2009, the luminosity of about 2.1034 cm -2 s -1; this represented the time the world record represents ( with TRISTAN only 5.1031 cm -2 s- 1 were achieved and in 2006 at the BaBar experiment at the PEP - II 1.2 × 1034 cm -2 s -1).