The Magazine of the University of Minnesota Duluth

Volume 22 • Number 2 • Summer 2005

 


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NEUTRINOS

SUPER SMALL AND HARD TO CATCH

            When a student signs up for Associate Professor Alec T. Habig's Introduction to Physics II or Experimental Methods courses they may not know quite what they are getting into. That's because Habig, in addition to teaching, also is the operations manager for the MINOS neutrino detector, and sometimes, students get to participate in the experiments. In fact, anywhere between eight and 15 graduate and undergraduate students in physics, electrical engineering and computer science can work on the project in any given semester.

            First they have to get there. An hour north of Duluth and a half-mile underground is the home of UMD's neutrino detector. After the ride in the narrow shaft, the tunnels of the Tower-Soudan mine, formerly an iron ore mine, open up to a bright space, about the size of an auditorium. That's where a $55 million particle physics experiment, part of an international research effort, is housed. The goal of the project is to learn the secrets of the neutrino, one of the least known particles of the subatomic world.

            Several discoveries over the past decade have drawn attention back to the neutrino. The MINOS experiments may help physicists understand the mysteries of elementary particle physics. They could learn more about how galaxies were created, how dying stars explode and how hydrogen, helium, and other light elements are formed.

            Neutrinos seem to magically change their types. The experiment at Soudan measures the rate of change, which give physicists a better idea of how their minute mass behaves. Neutrinos are so incredibly small and so hard to detect, it takes trillions and trillions to make meaningful observations. Successful experiments must have either an incredible amount of neutrinos or a lot of matter for neutrinos to run into.

            The UMD experiment uses bursts of trillions of neutrinos generated by a particle accelerator at Fermilab, 450 miles away. Fermilab takes careful aim then sends the neutrinos traveling underground until they crash into the Minnesota detector. The apparatus weighs 6,000 tons and is made up of 486 octagonal steel plates that stand upright like slices in a loaf of bread. Each plate is one inch thick and 30 feet wide.

            This experiment is intended to catch just a few of the neutrinos.

            "You need a light-year of lead to reliably stop a neutrino," said Habig. The project began in February 2005 when Fermilab began sending trillions of neutrinos in timed bursts toward Soudan. At first, hardly any neutrinos were detected but now the count is up to a few neutrinos a day "ringing" in the steel plates. Several UMD students helped wire the steel plates with fiber optic cord and connected the cord to computers. The computers then see the neutrinos colliding with steel as tiny bursts of light and separate the Fermilab neutrino path, which is relatively horizontal, with stray neutrinos which may filter down through the earth from outer space.

            The data from Soudan is expected to backup the results of another of Habig's neutrino experiments, Super-Kamiokande. Habig came to UMD from a research position at the Super-K site in Japan. Habig still participates in SNEWS (Supernova Early Warning System), which is a cooperative effort among the neutrino experiment sites around the world. They work together to provide an early warning of a supernova in our galaxy.

            All this effort will help physicists understand atom production in the aftermath of the Big Bang and in supernovas. Because neutrinos are essential to the nuclear reactions that change protons to neutrons and vice versa, they influence which elements form in what relative proportions. "That would have profound implications for our models of the early universe and for supernovas," said Habig. "It could change everything."

 

 
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