KEKB was a

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

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, Ibarak ...

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 symmetry) and P-symmetry ( parity symmetry). CP-symmetry states that the laws of physics should be t ...

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

Tsukuba is a city located in Ibaraki Prefecture, Japan. , the city had an estimated population of 244,528 in 108,669 households and a population density of 862 persons per km². The percentage of the population aged over 65 was 20.3%. The total ar ...

Ibaraki Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Ibaraki Prefecture has a population of 2,871,199 (1 June 2019) and has a geographic area of . Ibaraki Prefecture borders Fukushima Prefecture to the north, Tochigi Prefecture ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. It has been superseded by its upgrade, the

SuperKEKB SuperKEKB is a particle collider located at KEK (''High Energy Accelerator Research Organisation'') in Tsukuba, Ibaraki Prefecture, Japan. SuperKEKB collides electrons with positrons at the centre-of-momentum energy close to the mass of the Υ(4 ...

accelerator (located at the same site). The SuperKEKB is a

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a ...

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 In particle physics, a B-factory, or sometimes a beauty factory, is a particle collider experiment designed to produce and detect a large number of B mesons so that their properties and behavior can be measured with small statistical uncertainty. ...

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 ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

–

positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...

collider A collider is a type of particle accelerator which brings two opposing particle beams together such that the particles collide. Colliders may either be ring accelerators or linear accelerators. Colliders are used as a research tool in particle ...

, 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

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 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 Amy is a female given name, sometimes short for Amanda, Amelia, Amélie, or Amita. In French, the name is spelled ''"Aimée"''. People A–E * Amy Acker (born 1976), American actress * Amy Vera Ackman, also known as Mother Giovanni (1886– ...

. 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 (from Latin ''circumferens'', meaning "carrying around") is the perimeter of a circle or ellipse. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out to ...

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 i ...

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

INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 197 ...

Particle physics facilities Particle experiments

See also

References

External links