Pitt Physicist and Colleagues at Fermilab Launch Experiment to Discover Secrets of Neutrinos

PITTSBURGH— Frederick Reines, discoverer of the neutrino, described it as "the most tiny quantity of reality ever imagined by a human being." Neutrinos are at least ten million times lighter than electrons, but until now, their true mass could not be determined.

Today, a University of Pittsburgh physicist and her colleagues at the Department of Energy's Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., launched an experiment that will make the most precise measurements yet of the neutrino's physical properties. The Main Injector Neutrino Oscillation Search (MINOS) experiment also seeks to discover new phenomena, such as how neutrinos are related to the mysterious substance dark matter, which makes up about a third of the universe.

At 2:30 p.m., U.S. Speaker of the House of Representatives Dennis Hastert activated the Neutrinos at the Main Injector (NuMI) beam at Fermilab. The beam of particles will send neutrinos 450 miles in 2.5 milliseconds, through the earth, to a particle detector half a mile underground, in the Soudan iron mine in northeastern Minnesota.

"Neutrinos are by far the most abundant particles with mass in the universe," said Donna Naples, associate professor in the Department of Physics and Astronomy in Pitt's School of Arts and Sciences and a researcher in the experiment. "A lot of them were produced in the Big Bang and in the early universe, and because they interact so rarely, nothing happens to them—they just stick around." Although trillions of neutrinos produced in the sun and the atmosphere are constantly streaming around and through us, little is understood about them.

A better understanding of neutrinos could shed light on the universe's origin and ultimate fate; fusion, the source of the sun's energy; supernovas and energy production from stars; and dark matter.

As neutrinos travel through space and pass through planets, including Earth, they oscillate from one "flavor" to another. The NuMI beam will produce only one flavor of neutrino, so that researchers can measure changes in flavor at Fermilab's Near Detector and the Soudan mine's Far Detector. Naples and her colleagues will use such oscillations to determine the neutrino's mass.

Neutrinos can only be detected when they bump into atoms, a rare occurrence: More than a trillion man-made neutrinos will pass through the MINOS detector each year, but only about 1,500 of them each year will collide with atoms and be detectable.

The U.S. Department of Energy provided the major share of the funding for this research. Additional funding was provided by the National Science Foundation and the United Kingdom's Particle Physics and Astronomy Research Council.

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