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 $b \to s l^+ l^-$
• measurement of ϕ₃ using the $B \to D K, D \to K_S \pi^+ \pi^-$ 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 BB 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 short runs at the ϒ(5S) resonance to study B
s mesons as well as on the ϒ(3S) resonance to search for evidence of Dark Matter and the Higgs Boson.

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