Belle experiment

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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 experiment, is a multi-layer 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 multi-GeV momenta (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 bottom and charm mesons and tau lepton have been carried out and have resulted in over 200 publications in physics journals.

Highlights of the Belle experiment so far include the 1st 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 $φ 3$ using the $B \to D K, D \to K_S \pi^+ \pi^-$ Dalitz plot; measurement of the CKM quark mixing matrix elements $| V u b |$ and $| V c b |$ ; 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 $B \to \tau \nu$ and observations of a number of new particles including the X(3872).

The Belle experiment operates at the KEKB accelerator, the world's highest luminosity machine. The instantaneous luminosity exceeds $1.7 \times 10^{34}/cm^2/sec$ . The integrated luminosity is greater than $700~ fb^{-1}$ (in excess of 600 million $B \bar B$ meson pairs). Most data is recorded on the Upsilon(4S) resonance, which decays to pairs of B mesons (particles containing b-quarks). About 10% of the data is recorded below the Upsilon(4S) resonance in order to study backgrounds. In addition, Belle has carried out special short runs at the Upsilon(5S) resonance to study $B s$ mesons (particles with a b quark and s anti-quark) as well as on the Upsilon(3S) resonance to search for evidence of Dark Matter and the Higgs Boson.