Interactions News Wire #28-09
11 May 2009
http://www.interactions.org
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Source: KEK
Content: Press Release
Date Issued: 11 May 2009
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Using Crab Cavities, KEKB Breaks Luminosity World Record
A team of accelerator physicists at the KEK High Energy Physics Laboratory
in Tsukuba, Japan, has broken the world's luminosity record by utilizing
new accelerator devices called "crab cavities." The team at the KEKB
electron-positron collider, home to the world's highest luminosity
particle accelerator, installed the first pair of these futuristic
superconducting radio-frequency cavities over two years ago.
Until 2007, the electron and positron bunches in the KEKB accelerator
beams crossed at a 22 milliradian angle. The crossing angle itself has
been one of the novel features of KEKB design, providing an effective beam
separation after collision without a high detector background level, and
it has been successfully used to achieve its world luminosity record. To
boost the luminosity further, however, it was necessary to recover an
effective head-on collision while retaining the crossing angle.
To accomplish this goal, the KEKB researchers built special
superconducting radio-frequency (RF) cavities that kick each beam sideways
in the horizontal plane so that the bunches collide head-on at the
interaction point. These special RF cavities are called "crab cavities"
and were first suggested almost 30 years ago by R. Palmer for linear
electron-positron colliders. In 1989, K. Oide and K. Yokoya proposed the
use of crab cavities in storage rings. This was followed by designs and
prototype models of the crab cavity developed by K. Akai as a part of
collaboration efforts between the KEK and Cornell laboratories around
1992. In the 1990s detailed engineering and prototyping were done at KEKB
by K. Hosoyama's team, finally converging on the current design. The first
full-size cavities were developed after intense discussion and elaboration
and then installed in January 2007. The detailed commissioning of these
novel devices at KEKB started in February 2007. Recently, a breakthrough
was achieved by controlling the behaviour of off-energy beam particles
with special skew sextupole magnets. On May 6, 2009, KEKB broke the world
luminosity record and achieved a luminosity of 1.96 x 1034/cm2/sec using
the crab cavities. This new record is almost a factor of two higher than
the original design luminosity of KEKB. While this luminosity was being
recorded, the background remained in good condition and the data were
recorded smoothly in the Belle experiment.
The KEKB collider is used by researchers for the study of
matter-antimatter asymmetry of bottom (beauty) quarks and searches for new
physics at the Belle experiment, an international collaborative effort of
scientists from universities and research institutes. Since the beginning
of operation in 1999, the Belle experiment has reported a number of
fundamental discoveries concerning matter-antimatter asymmetry and rare
decays.
For the future, a super B Factory upgrade (called SuperKEKB) that will
build on the experience and hardware developed at KEKB to achieve a
luminosity higher by a factor of 40 is now being planned and designed in
Japan. The recent breakthrough at KEKB and its long history of world
luminosity records suggest that SuperKEKB will achieve its goals. A large
international collaboration has also been formed to upgrade the Belle
detector to observe the collisions at the SuperKEKB facility. The
SuperKEKB machine has the potential to discover physics beyond the
Standard Model in rare decays and unveil new kinds of matter-antimatter
asymmetry.
Media Contact
Youhei Morita, KEK Public Relations Office
+81 29-879-6047
