The first beam in the Large Hadron Collider (LHC) at CERN, Geneva was successfully steered around the full 27 kilometers of the world's most powerful particle accelerator on 10 September 2008. Protons will be eventually accelerated to 14 TeV for the collider experiments. These experiments at the world's highest energy will generate a state similar to the very early stages of the Big Bang, with which physicists will try to uncover some unknown particles, such as Higgs boson, the origin of the mass, or supersymmetric particles, one of the candidates of the dark matter of the Universe.
In addision to the energy of the particle beam, a parameter called "Luminosity", which describes the rate of particle collisions, is of particular importance at the colliders such as KEKB and LHC. Producing new particles or the rate of finding certain decay products of them are so rare that an efficiency of a collision becomes essential. One of effective schemes for increasing the luminosity at LHC is called "Crab Crossing". Beams in most colliders consist of a number of sets of particles called "bunches". Bunches in LHC, as well as in KEKB collides to each other by having a finite crossing angle. Having beam collisions with the crossing angles make the separation of the beams easy after the collisions . On the other hand, there will be limitations on the luminosity because these bunches do not overlap completely. Crab crossing had been devised to deal with the overlapping, making bunches tilted toward the middle line of the crossing orbits of two beams. Tilted bunches are effectively overlapped with the head-on collisions. Crab cavity is an instrument for tilting the beam bunches. KEK had developed these cavities prior to other institutes in the world, made two crab cavities in 2006 and has started an experiment on crab crossing at KEKB since 2007.
Following the effort at KEKB, scientists working for LHC also start thinking about usage of crab cavities for their detector. As LHC has much higher energy than KEKB, the cavities of the LHC require a several times higher voltages than those of the KEKB. Now a study group consisted by CERN staff and scientists in the USA is taking designs of LHC crab cavities. A collaboration is proposed between the researchers at KEKB and at LHC, to participate in designing and production those cavities.
Considering of such backgrounds, TV conferences were held between CERN and KEK on July 15 and August 5, 2008. Scientists relating this field in both laboratories participated in these conferences, having made wide-raging discussions as for improvements for the future, items for tests, performance of cavities and their problems. They agreed to delegate three scientists of KEK to the workshop for LHC crab cavity validation held at CERN on August 21, 2008. On the workshop there were detailed discussions on the status of experiments of the KEKB crab crossing and the operation of their cavities. The group from CERN discussed on their schedule for the realization of the crab crossing at CERN, the group from USA discussed on their designs and outputs of the cavities and the group from UK discussed on compact crab cavities they will need in future. In this December a scientist of CERN will visit KEK to take part in the operation of the KEKB crab crossing. The mutual cooperation on crab crossings between CERN and KEK is getting more and more strength, such like upgrades of the KEKB crab crossing, and tests items coming into an issue in LHC at KEKB crab crossing.
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