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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Monday, September 25, 2006

B_s meson: Matter to/from Antimatter 3 million times a second

Christoph Paus of MIT announcing the discovery at Fermilab (photo courtsey: Fermilab)

After 2 decades of painstaking research with monumentally precise technology, scientists of the CDF collaboration at the Department of Energy's Fermi National Accelerator Laboratory announced today that they have met the exacting standard to claim discovery of astonishingly rapid transitions of the B_s meson between matter and antimatter 3 trillion times a second.

Immediately after the Big Bang some 13 billion years ago equal amounts of matter and antimatter formed. Much of it quickly acted to annihilate the other, but for little-understood reasons a bit more matter than antimatter survived, providing the universe with the planets, stars and galaxies visible today. Particles that bridge the two worlds, such as the B_s (pronounced B-sub-s) meson, normally don't exist on their own but can be created in the great collisions generated by particle accelerators, which attempt to duplicate conditions close to the Big Bang. Studying the particles helps scientists understand the evolution of the universe.

The B_s meson consists of the heavy bottom quark bound by the strong nuclear interaction to a strange antiquark. The incredibly rapid commuting rate of the B_s meson particle had been predicted by the Standard Model, the successful but still incomplete theory aimed at explaining how matter and energy interact to form the visible universe. The discovery of this oscillatory behavior is thus another reinforcement of the Standard Model's durability.

Many different theoretical models of how the universe works at a fundamental level will now be confronted with the CDF discovery. The currently popular models of supersymmetry, for example, predict a much higher transition frequency than that observed by CDF, and those models will need to be reconsidered.

It must be recalled that scientists at Fermilab also discovered two of the most fundamental particles, the bottom quark in 1977 and in 1995 the top quark, one of the constituent particles of protons, which form the nuclei of atoms.

The results have been submitted in a paper to Physical Review Letters.

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