KEKB was a

particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies to contain them in well-defined particle beam, beams. Small accelerators are used for fundamental ...

used in the

Belle experiment The Belle experiment was a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers, at the High Energy Accelerator Research Organisation ( KEK) in Tsukuba, Ibara ...

to study

CP violation In particle physics, CP violation is a violation of CP-symmetry (or charge conjugation parity symmetry): the combination of C-symmetry (charge conjugation symmetry) and P-symmetry ( parity symmetry). CP-symmetry states that the laws of physics s ...

. KEKB was located at the '' KEK'' (''High Energy Accelerator Research Organisation'') in

Tsukuba is a city located in Ibaraki Prefecture, Japan. As of January 1, 2024, the city had an estimated population of 256,526 in 121,001 households and a population density of 900 persons per km2. The percentage of the population aged over 65 wa ...

Ibaraki Prefecture is a Prefectures of Japan, prefecture of Japan located in the Kantō region of Honshu. Ibaraki Prefecture has a population of 2,828,086 (1 July 2023) and has a geographic area of . Ibaraki Prefecture borders Fukushima Prefecture to the north, ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. It has been superseded by its upgrade, the SuperKEKB accelerator (located at the same site). The SuperKEKB is a

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

upgrade of KEKB. SuperKEKB had its first particle collisions in 2018. The SuperKEKB accelerator produces particle beams for the Belle II experiment, which is an upgrade of the Belle experiment (located at the same site as Belle). The Belle experiments studied b-quark hadrons to research CP violation. KEKB was called a B-factory for its copious production of B-mesons which provide a golden mode to study and measure the

due to its property of decaying into other lighter mesons. KEKB was basically an asymmetric

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

–

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

collider A collider is a type of particle accelerator that brings two opposing particle beams together such that the particles collide. Compared to other particle accelerators in which the moving particles collide with a stationary matter target, collid ...

, with

s having the energy of 8 GeV and

s having the energy of 3.5 GeV, giving 10.58 GeV centre-of-mass energy, which is equal to the mass of the Υ(4S) meson. There are basically two rings for

accelerating In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are vector quantities (in that they have magnit ...

s and

s. 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 In quantum field theory, and specifically quantum electrodynamics, vacuum polarization describes a process in which a background electromagnetic field produces virtual electron–positron pairs that change the distribution of charges and curr ...

around an electron and operated at center-of-mass energies between 50 and 61.4 GeV. There were three experiments at the old TRISTAN accelerator: Venus, Topaz, and AMY. The RF cavities in the HER use superconducting RF (SRF) technology, whereas the RF cavities in the LER use a normal conducting design denoted ARES.K. Akai et al., "RF systems for the KEK B-Factory", Nuclear Instruments and Methods in Physics Research A 499 (2003) 45–65
/ref> The

circumference In geometry, the circumference () is the perimeter of a circle or ellipse. The circumference is the arc length of the circle, as if it were opened up and straightened out to a line segment. More generally, the perimeter is the curve length arou ...

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

is located. The other areas (called "Fuji", "Nikko" and "Oho") are currently not actively used by an experiment. Since the energy of the

s and

s is asymmetric, the B meson pairs are created with a

Lorentz boost In physics, the Lorentz transformations are a six-parameter family of linear transformations from a coordinate frame in spacetime to another frame that moves at a constant velocity relative to the former. The respective inverse transformation ...

βγ of 0.425, allowing measurements of the B meson decay times via the distance from the (known) collision point. KEKB Ring 3km circumference

KEKB's leading finite crossing angle interaction design provides its high luminosity. In the last upgrade, KEKB installed crab cavities on each of its accelerating beams to rotate the bunches of accelerating electrons or positrons, hoping to further increase its luminosity. However, the improvement is not clear and currently under tuning.

References

{{reflist

External links

KEKB experiment
record on

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Particle physics facilities Particle experiments

See also

References

External links