April 1, 1999
Vol. 18 No. 13

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    [james cronin and alan watson] by jason smithJames Cronin, a Chicago Nobel laureate (at left) and Alan Watson of the University of Leeds will lead the international project to track cosmic rays at the newly dedicated Pierre Auger Observatory.

    Cronin leads international project to track cosmic rays at Auger Observatory

    By Steve Koppes
    News Office

    Scientists will need two detectors the size of Rhode Island to track down the mysterious source of rare but extremely powerful, high-energy, cosmic rays that periodically bombard Earth.

    These giant detectors will be part of the new Pierre Auger Observatory, an international project led by Chicago Nobel laureate James Cronin and University of Leeds researcher Alan Watson.

    Cronin and Watson took part in a groundbreaking ceremony Wednesday, March 17, in Argentina’s Mendoza Providence, the Auger Observatory’s Southern Hemisphere site. Construction will begin soon on a large-scale prototype detector array that could go into operation by the end of the year.

    The Auger Observatory will practice a new form of astronomy rooted in particle physics, Cronin said. “Nature is trying to tell us something by showing us something extraordinary,” he said. “These are the most energetic particles in the universe. There’s nothing more energetic.”

    The groundbreaking ceremony puts the observatory one step closer to realization, following long and arduous efforts to build a coalition of 250 scientists in 19 nations to support the $50 million project.

    “I have worked on the highest-energy cosmic rays for 35 years and on the Auger Project for seven and a half,” Watson said. “I passionately want to find out where the highest-energy cosmic rays come from, and I think this project is the most effective way to do it.”

    Cronin and Watson named the Auger Observatory for the scientist who discovered showers of cosmic ray particles in 1938. Auger conducted research here at Chicago in 1942, even launching hot-air balloon experiments from Stagg Field to study cosmic rays.

    His daughter, Mariette Auger Berl, who studied arts and literature at Chicago before joining the Free French Forces during World War II, attended the recent groundbreaking ceremony in Argentina.

    Both the Argentina and Utah sites of the Auger Observatory will consist of 1,600 particle detector stations covering 1,860 square miles. The stations will sit approximately one mile apart, each equipped with a 3,000-gallon water tank rigged with instruments to measure the number of particles passing through. Central computers will combine measurements of the number of particles and their arrival times at each station to determine the direction and energy of the original cosmic rays that set off the shower.

    The second detection system will use finely tuned light sensors that will be able to detect the faint glow caused by the collisions between shower particles and air molecules on dark, moonless nights.

    Low-energy cosmic rays continually strike every square yard of the Earth from all directions. The Auger Observatory will seek cosmic rays that have more than 100 million times more energy than the particles produced in the world’s most powerful particle accelerator at Fermilab. Only one of these particles strikes any square kilometer (six-tenths of a mile) area in a century.

    These particles can only be directly observed above Earth’s atmosphere. The Auger Observatory will detect them indirectly. When cosmic ray particles strike the atmosphere, they collide with air molecules, producing a shower containing many millions of particles that fall to Earth over a wide area.

    A few high-energy cosmic ray showers already have been detected with existing arrays. The Fly’s Eye cosmic ray detector in Utah detected the most powerful one ever recorded on Oct. 15, 1991. The shower packed 300 million times more energy than the Fermilab particle accelerator can generate.

    Even the runner-up event, the detection at Japan’s Akeno Giant Air Shower Array on Dec. 3, 1993, contained energy far beyond what even the most violent exploding stars could achieve.

    Scientists can only speculate about the causes of these high-energy particle bursts. One theory suggests they result from topological defects––stresses and strains in space comparable to faulting and folding within the Earth’s crust. Although ideas abound in scientific literature, Cronin said, “we are nowhere near understanding these things.”