![The BELLE Detector](https://upload.wikimedia.org/wikipedia/commons/d/d8/The_BELLE_Detector.jpg)
The Belle experiment was a
particle physics
Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers, at the High Energy Accelerator Research Organisation (
KEK
, known as KEK, is a Japanese organization whose purpose is to operate the largest particle physics laboratory in Japan, situated in Tsukuba, Ibaraki prefecture. It was established in 1997. The term "KEK" is also used to refer to the laboratory ...
) 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 Prefectures of Japan, 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, ...
,
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 ...
. The experiment ran from 1999 to 2010.
The Belle detector was located at the collision point of the asymmetric-energy
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 kn ...
–
positron 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 particl ...
,
KEKB KEKB may refer to:
* KEKB (accelerator)
* KEKB (FM)
KEKB is a radio station serving Grand Junction, Colorado and its vicinity with a country music format. This station broadcasts on FM frequency 99.9 MHz and is under ownership of Townsquare ...
. Belle at KEKB together with the
BaBar experiment
The BaBar experiment, or simply BaBar, is an international collaboration of more than 500 physicists and engineers studying the subatomic world at energies of approximately ten times the rest mass of a proton (~10 GeV). Its design was motiva ...
at the
PEP-II
SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center,
is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departm ...
accelerator at
SLAC
SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center,
is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departme ...
were known as the
B-factories as they collided electrons with positrons at the center-of-momentum energy equal to the mass of the
(4S) resonance
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
which decays to pairs of
B meson
In particle physics, B mesons are mesons composed of a bottom antiquark and either an up (), down (), strange () or charm quark (). The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark' ...
s.
The Belle detector was a
hermetic
Hermetic or related forms may refer to:
* of or related to the ancient Greek Olympian god Hermes
* of or related to Hermes Trismegistus, a legendary Hellenistic figure based on the Greek god Hermes and the Egyptian god Thoth
** , the ancient and m ...
multilayer
particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing particles, such as those produced by nuc ...
with large
solid angle
In geometry, a solid angle (symbol: ) is a measure of the amount of the field of view from some particular point that a given object covers. That is, it is a measure of how large the object appears to an observer looking from that point.
The poi ...
coverage, vertex location with precision on the order of tens of micrometres (provided by a silicon vertex detector), good distinction between
pion
In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: ) is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more gene ...
s and
kaon
KAON (Karlsruhe ontology) is an ontology infrastructure developed by the University of Karlsruhe and the Research Center for Information Technologies in Karlsruhe.
Its first incarnation was developed in 2002 and supported an enhanced version of ...
s in the momenta range from 100
MeV/c to few GeV/c (provided by a
Cherenkov detector), and a few-percent precision electromagnetic
calorimeter
A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimete ...
(made of
CsI(
Tl)
scintillating crystals).
The
Belle II experiment is an upgrade of Belle that was approved in June 2010. It is currently being commissioned, and is anticipated to start operation in 2018. Belle II is located at
SuperKEKB (an upgraded
KEKB KEKB may refer to:
* KEKB (accelerator)
* KEKB (FM)
KEKB is a radio station serving Grand Junction, Colorado and its vicinity with a country music format. This station broadcasts on FM frequency 99.9 MHz and is under ownership of Townsquare ...
accelerator) which is intended to provide a factor 40 larger integrated luminosity.
Results
![Belle Central Drift Chamber](https://upload.wikimedia.org/wikipedia/commons/e/e3/Belle_Central_Drift_Chamber.jpg)
The experiment was motivated by the search for
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 the ...
. However the experiment also performed extensive studies of rare decays, searches for exotic particles and precision measurements of the properties of
D meson
The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called "F mesons" prior to 1986.
Overview
The D mesons were discove ...
s, and
tau particles.
The experiment has resulted in almost 300 publications in physics journals.
Highlights of the Belle experiment include
* an observation of large CP-violation in the neutral
B meson
In particle physics, B mesons are mesons composed of a bottom antiquark and either an up (), down (), strange () or charm quark (). The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark' ...
system
* measurement of the branching fraction of inclusive
decays
* observation of the
transition with
and
* measurement of
using the
Dalitz plot
* measurement of the
CKM quark mixing matrix elements
and
* observation of direct CP-violation in
and
* observation of
transitions
* evidence for
* observations of a number of new particles including the
X(3872) The X(3872) is an exotic meson candidate with a mass of 3871.68 MeV/c2 which does not fit into the quark model because of its quantum numbers. It was first discovered in 2003 by the Belle experiment in Japan and later confirmed by several other exp ...
Data samples
The
KEKB KEKB may refer to:
* KEKB (accelerator)
* KEKB (FM)
KEKB is a radio station serving Grand Junction, Colorado and its vicinity with a country music format. This station broadcasts on FM frequency 99.9 MHz and is under ownership of Townsquare ...
accelerator was the world's highest
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 st ...
machine at the time. A large fraction of the data was collected at the (4S). The instantaneous luminosity exceeded . The
integrated luminosity collected at the (4S) mass was about (corresponding to 771 million meson pairs). About 10% of the data was recorded below the (4S) resonance in order to study backgrounds. In addition, KEKB carried out special runs at the
(5S) resonance to study
mesons as well as on the
(1S),
(2S) and
(3S) resonances to search for evidence of
Dark Matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not a ...
and the
Higgs Boson. The samples of
(1S),
(2S) and
(5S) collected by Belle are the world largest samples available.
See also
*
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. T ...
*
– oscillation
References
External links
Official Belle WebsiteBelle II Collaboration WebsiteBelle II Public Website*Record fo
KEK-BF-BELLEExperiment 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 1970 ...
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Particle experiments
B physics