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Laser creates billions of antimatter particles

Wednesday, 19 November 2008

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LLNL laser facility

Positron factory: Physicist Hui Chen sets up targets for the anti-matter experiment at the LLNL laser facility.

Credit: LLNL

SYDNEY: By shooting a laser through a gold disc no bigger than the head of a drawing pin, physicists have created more than 100 billion particles of antimatter.

The ability to create vast numbers of positrons in the laboratory opens the door to new avenues of research, they say. These include an understanding of the physics behind black holes, gamma ray bursts and why more matter than antimatter survived the Big Bang.

Super-sized portion of positrons

"We've detected far more antimatter than anyone else has ever measured in a laser experiment," said Hui Chen, a physicist at the Lawrence Livermore National Laboratory (LLNL) in California, U.S., who led the experiment. "We've demonstrated the creation of a significant number of positrons using a short-pulse laser."

Previous experiments made smaller quantities of positrons using lasers and paper-thin targets – but new simulations showed that millimetre-thick gold could be a far more effective source, said the researchers, who report their finding this week at the American Physical Society's Division of Plasma Physics Meeting in Dallas, South Carolina.

Chen and her team used a short, ultra-intense laser to irradiate a millimetre-thick gold target.

In the experimental set-up, the laser ionises and accelerates electrons, which are driven right through the gold target. On their way, the electrons interact with the gold nuclei, which serve as a catalyst to create positrons.

Electron's opposite number

The electrons give off packets of pure energy, which decay into matter and antimatter, following the predictions of Einstein's famous equation that relates matter and energy. By concentrating the energy in space and time, the laser produces positrons more rapidly and in greater density than ever before in the laboratory.

Positrons are the antimatter equivalent to the electron, and behave in a similar way, though they have the opposite charge (see, New twist to matter-antimatter mystery, Cosmos Online).

The researchers took advantage of this property to detect them, by using a typical device to detect electrons (a spectrometer) and equipping it to detect particles with opposite polarity as well.

"By creating this much antimatter, we can study in more detail whether antimatter really is just like matter, and perhaps gain more clues as to why the universe we see has more matter than antimatter," said LLNL team member Peter Beiersdorfer.