U physicists join international atomic particle study in state ore mine

Troy Pieper

For almost 100 years, the Soudan mine in Tower, Minn., yielded the purest iron ore in the country. Now University researchers will mine knowledge that could put them on the forefront of physics research.

In the Soudan Underground Laboratory, physicists from the University and 29 other institutions will attempt to discover whether the elusive atomic particles known as neutrinos have mass. The study could allow “a new and very exciting area of scientific exploration to open up,” said Stanley Wojcicki, Stanford University physicist and principal investigator for the Main Injector Neutrino Oscillation Search.

Starting in 2005, pulses of trillions of neutrinos will be fired every 1.9 seconds from an Illinois particle accelerator. They will travel through 445 miles of earth to meet 10 million pounds of steel half a mile underground at the Soudan mine. The experiment will cost the U.S. Department of Energy, the United Kingdom and the state of Minnesota $175 million.

MINOS will aim to discover whether neutrinos change their character, or “flavor,” between Chicago and the Soudan mine, said University physics professor Earl Peterson.

“We want to know what the family ties between neutrinos are,” he said, “just as we already know (those) between quarks, the building blocks of protons and neutrons.”

Neutrinos have no charge and are so small they can pass uninterrupted “through several light-years of iron,” Peterson said. After the particles are fired from the Ferme National Accelerator Laboratory in Batavia, Ill., they will travel through three states in a fraction of a second before striking the MINOS receptacle.

Of the trillions of neutrinos in each pulse, approximately one neutrino every two hours will collide with the apparatus, Peterson said. When they do, they will produce a pattern of electrical signals in the detector. Tiny tracks of light will identify the neutrinos.

If the neutrinos change, it means they have mass. If they have mass, it means two important things.

“How the universe arranged itself after the big bang depends on the masses of particles,” Peterson said.

Neutrinos with mass would give scientists insight into the formation of stars and galaxies throughout the universe. If neutrinos have mass, scientists will also have found a portion of the universe’s dark matter – matter that can’t be seen but is known to exist by the gravitational force it exerts. Stars and planets make up approximately 10 percent of the total mass of the universe; dark matter makes up approximately 80 percent or 90 percent.

A working mine from the 1880s to the 1960s, Soudan was donated to the state in 1963 by U.S. Steel, and the state preserved the national historic site as an educational facility and state park. In 1980, physicists became attracted to the mine as a site for a physics laboratory because its depth shields highly sensitive energy detectors from cosmic rays.

The Soudan lab is also home to an experiment called the Cryogenic Dark Matter Search II, which looks for weakly interacting massive particles, another possible contributor to dark matter.

Amid the science, visitors touring the Soudan Underground Mine State Park can also see a painting on one wall of the main cavern. Minneapolis artist Joseph Giannetti created the mural at the suggestion of University physicist Marvin Marshak’s wife.

“My dream was to do a mural that couldn’t be torn down and would last forever,” Giannetti said. Started last October, the 25- by 60-foot work features a blazing sun centerpiece with concentric waves of scientific symbols, words such as “infinity” in several languages, faces of early physicists and old mining tools.

Giannetti was on hand for the MINOS dedication ceremony last week, when he explained his mural as signifying “the enormous energy in the universe that is constantly changing form.”

Allen Garber, commissioner of the Minnesota Derpartment of Natural Resources, highlighted the changes MINOS brings to Soudan.

In addition to improving the area’s economic vitality, “Soudan provides recreational and educational opportunities for park visitors to learn about the past and the future,” Garber said.

U.S. Rep. James Oberstar, D-Chisholm, praised the project for its contribution to the pursuit of knowledge and for “stimulating the curiosity of young minds.”

Troy Pieper welcomes comments at [email protected]