Belle experiment

Not to be confused withBell testexperiments, which demonstrate some of the counterintuitive features of quantum physics.

The Belle detector in Tsukuba Hall,KEK

TheBelle experimentwas aparticle physicsexperiment conducted by theBelle Collaboration,an international collaboration of more than 400 physicists and engineers, at the High Energy Accelerator Research Organisation (KEK) inTsukuba,Ibaraki Prefecture,Japan.The experiment ran from 1999 to 2010.

The Belle detector was located at the collision point of the asymmetric-energyelectron–positroncollider,KEKB.Belle at KEKB together with theBaBar experimentat thePEP-IIaccelerator atSLACwere known as theB-factoriesas they collided electrons with positrons at the center-of-momentum energy equal to the mass of the
ϒ
(4S)resonancewhich decays to pairs ofB mesons.

The Belle detector was ahermeticmultilayerparticle detectorwith largesolid anglecoverage, vertex location with precision on the order of tens of micrometres (provided by a silicon vertex detector), good distinction betweenpionsandkaonsin the momenta range from 100MeV/cto few GeV/c (provided by aCherenkovdetector), and a few-percent precision electromagneticcalorimeter(made ofCsI(Tl)scintillating crystals).

TheBelle II experimentis 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 atSuperKEKB(an upgradedKEKBaccelerator) which is intended to provide a factor 40 larger integrated luminosity.

Results

The retired central drift tracking chamber from Belle, now exhibited at theNational Museum of Nature and Science.

The experiment was motivated by the search forCP-violation.However the experiment also performed extensive studies of rare decays, searches for exotic particles and precision measurements of the properties ofD mesons,andtau 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 neutralB mesonsystem
• measurement of the branching fraction of inclusive$B\to X_{s}\gamma$decays
• observation of the$b\to sl^{+}l^{-}$transition with$B\to Kl^{+}l^{-}$and$B\to K^{*}l^{+}l^{-}$
• measurement of$\phi _{3}$using the$B\to DK,D\to K_{S}\pi ^{+}\pi ^{-}$Dalitz plot
• measurement of theCKM quark mi xing matrixelements$|V_{ub}|$and$|V_{cb}|$
• observation of direct CP-violation in$B^{0}\to \pi ^{+}\pi ^{-}$and$B^{0}\to K^{-}\pi ^{+}$
• observation of$b\to d$transitions
• evidence for$B\to \tau \nu$
• observations of a number of new particles including theX(3872)

Data samples

TheKEKBaccelerator was the world's highestluminositymachine at the time.A large fraction of the data was collected at the
ϒ
(4S). The instantaneous luminosity exceeded2.11×10³⁴cm⁻²·s⁻¹.Theintegrated luminositycollected at the
ϒ
(4S) mass was about710fb⁻¹(corresponding to 771 million
B

B
meson pairs). About 10% of the data was recorded below the
ϒ
(4S) resonance in order to study backgrounds. In addition, KEKB carried out special runs at the
ϒ
(5S)resonance to study
B
_smesonsas well as on the
ϒ
(1S),
ϒ
(2S)and
ϒ
(3S)resonances to search for evidence ofDark Matterand theHiggs Boson.The samples of
ϒ
(1S),
ϒ
(2S)and
ϒ
(5S)collected by Belle are the world largest samples available.

See also

• B-factory
• 
  B
  –
  B
  oscillation

External links

• Official Belle Website
• Belle II Collaboration Website
• Belle II Public Website
• Record forKEK-BF-BELLEExperiment onINSPIRE-HEP