Belle experiment

The Belle experiment is a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers investigating CP-violation effects at the High Energy Accelerator Research Organisation (KEK) in Tsukuba, Ibaraki Prefecture, Japan.

The Belle detector, located at the collision point of the
e⁻

e⁺
asymmetric-energy collider (KEKB), is a multilayer particle detector. Its large solid angle coverage, vertex location with precision on the order of tens of micrometres (provided by a silicon vertex detector), good pion–kaon separation at the momenta range from 100 MeV/c till few GeV/c (provided by a novel Cherenkov detector), and few-percent precision electromagnetic calorimetry (CsI(Tl) scintillating crystals) allow for many other scientific searches apart from CP-violation. Extensive studies of rare decays, searches for exotic particles and precision measurements of B mesons, D mesons, and tau particles have been carried out and have resulted in almost 300 publications in physics journals.

Highlights of the Belle experiment so far include

• the first observation of CP-violation outside of the kaon system (2001)
• observation of: $B\to K^{*}l^{+}l^{-}$ and $b\to sl^{+}l^{-}$
• measurement of $\phi _{3}$ using the $B\to DK,D\to K_{S}\pi ^{+}\pi ^{-}$ Dalitz plot
• measurement of the CKM quark mixing matrix elements $|V_{ub}|$ 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 the X(3872)

The Belle experiment operated at the KEKB accelerator, the world's highest luminosity machine. The instantaneous luminosity exceeded 2.11×10³⁴ cm⁻²·s⁻¹. The integrated luminosity collected at the
ϒ
(4S) resonance mass is ~710 fb⁻¹ (corresponds to 771 million
B

B
meson pairs). Most data is recorded on the
ϒ
(4S) resonance, which decays to pairs of B mesons. About 10% of the data is recorded below the
ϒ
(4S) resonance in order to study backgrounds. In addition, Belle has carried out special runs at the
ϒ
(5S) resonance to study
B
_s mesons as well as on the
ϒ
(1S),
ϒ
(2S) and
ϒ
(3S) resonances to search for evidence of Dark Matter and the Higgs Boson. The samples of
ϒ
(1S),
ϒ
(2S) and
ϒ
(5S) collected by Belle are the world largest samples available.

The Belle II B-factory, an upgraded facility with two orders of magnitude more luminosity, has been approved in June 2010. The design and construction work is ongoing.

See also

• B-factory
• 
  B
  –
  B
  oscillation

External links

• Official Belle Website
• Official Belle 2 Website