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Media Relations
Office of University Relations
Louisiana State University
Baton Rouge, Louisiana

Contact:
Rob Anderson, , 225-578-3871

01/09/2004

Catch a Falling Ray

The mention of Argentina conjures any number of exotic or dramatic images ...
Eva Peron ... dancing the tango ... gauchos riding the plains ... falling
high-energy cosmic rays.

Well, perhaps high-energy cosmic rays haven't worked their way into the travel
brochures or spawned a Broadway musical just yet. Nevertheless, these rays --
tiny particles from space that regularly pelt the earth -- are the subject of
one of the largest-scale scientific studies of its kind ever conducted, and one
of the first parts of this project is now up and running in Argentina.

On a massive area of open plains just east of the Andes Mountains -- a region
known as Pampa Amarilla -- a group of LSU professors, post-doctoral researchers
and graduate students have been working on this $100 million cosmic-ray study
with a broad international coalition at the new Pierre Auger Observatory.

The international coalition consists of some 250 scientists from 14 countries.
The Auger facility, when completed, will span some 1,200 square miles and
include more than 1,600 water tank detectors and several other structures,
including a specialized observatory with 24 optical telescopes. The facility is
managed by scientists from the Department of Energy's Fermi National Accelerator
Laboratory in Chicago.

With the recent commissioning of its 100th water tank detector, the Auger
Observatory became the largest cosmic-ray experiment ever conducted. It
continues to expand, and completion of the entire Argentina facility is expected
in 2005.

LSU Associate Professor of Physics James Matthews, Dept. of Physics and
Astronomy Chair Roger McNeil, postdoctoral researchers Rishi Meyhandan and Troy
Porter, and several graduate students are helping to build this new facility,
analyze the data gathered there and develop equipment and computer software and
programming to aid in the experiments.

The background work on the project began more than 10 years ago, but the
Argentinian facility only recently began operating and collecting data. Indeed,
the LSU group is now analyzing the first round of information gathered at the
facility.

A Cosmic Mystery

The project is large in scope because high-energy cosmic rays have baffled
scientists for years and solving the mystery behind them requires a massive
effort, explains Matthews. The structure of lower-energy rays -- protons,
nuclei, etc. -- has been understood for some time, but scientists "don't even
know what the highest energy rays are or where they come from," he says.

"The only thing we know for sure about the high-energy rays is that they exist,"
Matthews says. "So, the best way to understand them is to collect and measure
them ... let them tell us what they are and where they are from."

According to Matthews, cosmic rays were discovered more than a century ago. They
strike the Earth from all different directions, all of the time, and they come
in a range of "energies" that measure not only how fast they move, but how much
"punch" they pack. Lower-energy rays are common, but high-energy rays are
uncommon and have energy levels so high that they cannot be produced on earth.

"The highest energy rays are more than a billion times more energetic than any
particles that can be produced in terrestrial (particle) accelerators," Matthews
says. "It's difficult to even imagine how to get particles to such energies."

Rare rays

Because the particles are so rare, collecting or studying them individually --
with a detector in space, for instance -- would take "something very huge,"
Matthews says.

"If Tiger Stadium were floating in space, it might catch one every 20 years or
so," he says.

However, Matthews says, there are two dependable ways to detect them. Each makes
use of the fact that, when a high-energy cosmic ray strikes the earth's
atmosphere, it blasts apart into a shower of particles that fall to the ground,
primarily in the form of electrons.

First, it is possible to observe the shower that develops in the atmosphere when
the rays hit. Matthews says that the shower produces a weak fluorescence -- "a
line of faintly glowing atmosphere" -- that can be observed with the special
"Fly's-Eye" fluorescence telescopes that observe the sky in all directions.
Second, it is possible to collect or detect the falling particles using
water-tank detectors widely dispersed on the ground.

If the time it takes these "lines of fluorescence" to be produced, and
their length known, can the velocity of the particles be established?
(uh ho!!! faster than "c" !!!!!!!!!!)

Jim G