High Resolution Fly's Eye Cosmic Ray Detector facts for kids

The High Resolution Fly's Eye, also known as HiRes, was a special observatory that studied tiny, super-fast particles from space called ultra-high-energy cosmic rays. It worked in the desert of western Utah from May 1997 to April 2006.

HiRes used a clever method called atmospheric fluorescence. This means it looked for faint flashes of light made when cosmic rays hit the Earth's atmosphere. This technique was first used by scientists in Utah with earlier projects like the Volcano Ranch experiment and the first Fly's Eye experiment.

How HiRes Was Built

The High Resolution Fly's Eye was an improved version of the original Fly's Eye. It used bigger mirrors and could see smaller details, which is why it was called "High Resolution."

Early Tests and Prototypes

Before the main HiRes observatory was built, a test version ran from 1993 to 1996. It was set up at the same spot as the first Fly's Eye experiment. This prototype looked at a narrow slice of the sky.

This test setup was part of the first "hybrid experiment." This means it collected information in two ways:

• It watched the "air shower" – a cascade of particles created when a cosmic ray hit the atmosphere.
• It also measured the cosmic ray's "footprint" on the ground and even 3 meters below the surface.

The HiRes prototype was taken apart in early 1997 to become part of the final HiRes observatory.

The Two HiRes Sites

The final HiRes observatory had two main sites. They were 12.6 kilometers (about 7.8 miles) apart. Both sites were on hilltops in the Dugway Proving Ground, which is a U.S. Army test area in the western Utah desert.

• HiRes-I was on Five Mile Hill. It had a ring of 22 telescopes. These telescopes looked at the sky from 3 to 17 degrees above the horizon. HiRes-I used special electronics to take a quick "snapshot" of the air showers.
• HiRes-II was on Camel's Back Ridge. It had two rings of telescopes that could look higher into the atmosphere, from 3 to 31 degrees above the horizon. HiRes-II used different electronics that could essentially make "movies" of the cosmic ray events.

Both observatory sites could see in all directions (360 degrees). They worked independently on clear nights when there was no moon. HiRes was able to collect data about 10% of the time.

Amazing Discoveries

The HiRes experiment made a very important discovery. It was the first to observe something called the Greisen–Zatsepin–Kuzmin limit (GZK cutoff).

The GZK Limit Explained

The GZK cutoff is like a speed limit for the highest energy cosmic rays. It shows that these super-fast particles lose energy when they travel through space and bump into the faint glow left over from the Big Bang, called the cosmic microwave background. This means the universe becomes "opaque" (like a fog) to these extremely high-energy particles, stopping them from traveling forever.

In 2010, the final results from the HiRes experiment confirmed that the GZK cutoff is real.

What Came Next?

After HiRes and another experiment called the Akeno Giant Air Shower Array (AGASA), scientists built a new project called the Telescope Array Project. This project started collecting data in central Utah in 2007.

Another similar observatory is the Pierre Auger Observatory. It uses a different type of detector, called water-Cherenkov detectors, and started collecting data in 2004.

Recognizing the Scientists

Dr. Pierre Sokolsky and Dr. George Cassidy, both from the University of Utah, were honored for their important work on the HiRes experiment. They received the 2007 Panofsky Prize, which is a major award in physics.