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Interactions News Wire #11-07
5 March 2007  http://www.interactions.org
Source: High Energy Accelerator Research Organization (KEK)
Content: Press Release
Date Issued: 2 March 2007

Belle Confirms Quantum Entanglement at 10 Billion Electron Volts

In 1935 Albert Einstein and collaborators Boris Podolski and Nathan Rosen (EPR) wrote a celebrated paper on "entangled states": systems that, according to quantum mechanics, must be treated as a single unit even if their pieces are far apart. They concluded that quantum mechanics cannot be a complete theory; this suggests that additional quantities ("hidden variables") are required to describe reality. Further theoretical and extensive experimental work for the last seven decades has ruled out most simple versions of the hidden variable idea and suggests that quantum mechanical entanglement is a feature of the world.
Previous experimental tests of quantum mechanics have been carried out with optical energy photons, systems of atoms and kaons (particles containing strange quarks). Using pairs of B mesons (particles containing b quarks) the Belle experiment at KEK in Tsukuba, Japan has submitted a paper to Physical Review Letters, a leading US physics journal, which reports tests of quantum mechanics at the 10 billion electron-volt energy scale, which is significantly beyond the energy scale of previous tests.
Belle tests quantum mechanics by measuring the time dependence of decays of B mesons that are produced from the decays of the Upsilon(4S) resonance at the KEKB electron-positron collider. The decay products are reconstructed in the Belle detector. By closely examining the time dependence of pairs of B meson decays, the Belle experimenters conclusively rule out two alternatives to quantum mechanics; spontaneous disentanglement in which the two B mesons evolve independently and another alternative called the Pompili-Selleri model.
The Belle results are consistent with the prediction of quantum mechanics, where each pair of B-mesons behaves as a single "entangled" object. The data have now been placed on public record, and can be used to test any other alternative models that are devised by theorists in the future.
The Belle experiment is a collaborative effort of scientists from universities and laboratories in America, Asia, Australia, and Europe. The experiment operates at the KEK High Energy Physics Laboratory in Tsukuba, Japan, which is home to the world's highest luminosity particle accelerator.

Media Contact
Youhei Morita, KEK Public Relations Office
+81 29-879-6047

For more details
Belle group: http://belle.kek.jp/
The press release including images: http://www.kek.jp/intra-e/press/2007/BellePress9e.html