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In this issue:
A 100-Telescope Net for Gamma Rays
In the News: Fermilab Collider Experiments Discover Rare Single Top Quark

SLAC Today

Tuesday - March 10, 2009

A 100-Telescope Net for Gamma Rays

An artist's conception of a future gamma-ray system. (Image courtesy of J. Buckley, University of Washington. Click for larger image.)

One hundred telescopes, stretching one after another in every direction for half a kilometer, point toward the heavens every night to observe the most energetic processes in the universe—everything from supermassive black holes to exploding stars. For now, this tableau is just a dream. But a team of SLACers, in collaboration with researchers around the world, are working to make it a reality.

"This is an exciting project, one that will reveal the universe's most energetic gamma rays: the ones above one tera-electron volt," said astrophysicist Stefan Funk of the Kavli Institute for Particle Astrophysics and Cosmology. "But the project is still in the very initial stages, and there's much to be done."

Funk is a member of the Advanced Gamma-ray Imaging System, or AGIS, collaboration, which is designing the next big gamma-ray telescope. With ten times more sensitivity to gamma rays than previous experiments—including the Fermi Gamma-ray Space Telescope—the array will detect sources that are too distant and too weak for current telescopes to pick up, adding missing detail to scientists' gamma-ray map of the universe. The AGIS telescope will also be substantially better at pinpointing the direction from which each gamma ray came, helping researchers to better understand the origin of the rays and how these ultra-high energy particles are produced. The project is still in the early phases of research and development, and has not yet secured funding outside the collaborators' home institutions. If all goes according to plan, the collaboration will start building the array around 2014.  Read more...

In the News: Fermilab Collider Experiments Discover Rare Single Top Quark

(Image - DZero top quark event)
A single top quark candidate event recorded by the DZero collaboration. The top quark decayed into a bottom quark, a muon, and a neutrino. (Image courtesy of the DZero Collaboration. Click for larger image.)

Scientists at the Department of Energy's Fermilab have observed a new subatomic process. In particle collisions produced by the Tevatron collider, currently the world's most powerful operating particle accelerator, two teams of scientists found single top quarks. The discovery has significance for the ongoing search for the Higgs particle.

Previously, top quarks had only been observed when produced by the strong nuclear force. That interaction leads to the production of pairs of top quarks. The production of single top quarks, which involves the weak nuclear force and happens almost as often as the strong force production, is harder to identify experimentally. Now, scientists working on the CDF and DZero collider experiments at Fermilab achieved this feat, almost 14 years to the day of the top quark discovery at Fermilab in 1995.

Searching for single-top production makes finding a needle in a haystack look easy. Only one in every 20 billion proton-antiproton collisions produces a single top quark. Even worse, the signal of these rare occurrences is easily mimicked by other "background" processes that occur at much higher rates.

"Observation of the single top quark production is an important milestone for the Tevatron program," says Dennis Kovar, associate director of the DOE Office of Science for High Energy Physics. "The highly sensitive and successful analysis is an important step in the search for the Higgs."  Read more in Symmetry Breaking...

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