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|At UMD, graduate students Adam Moren (left), and Kyle Thomsen (right) work with Professor Alec Habig (center) to interpret the neutrino detector data. Plastic cells of extruded, highly reflective plastic PVC, like the ones shown, are filled with liquid scintillatorand installed at Ash River to collect neutrino impact patterns.|
|Scientists use the NuMI (Neutrinos at the Main Injector) horn to focus and steer a beam of particles that eventually decay into neutrinos.|
|Plastic cells ready for installation at the Ash River site|
The NOvA experiment consists of two huge particle detectors placed 500 miles apart, and its job is to explore the properties of an intense beam of ghostly particles called neutrinos. Neutrinos are abundant in nature, but they very rarely interact with other matter. Studying them could yield crucial information about the early moments of the universe.
UMD AND THE PROJECT
Habig is a member of the NOvA collaboration, a group of 208 scientists from 38 institutions in the United States, Brazil, the Czech Republic, Greece, India, Russia and the United Kingdom. Habig is the convener of the ‘exotics’ analysis working group with the Ash River project. His group analyses the data to look for information that is out of the ordinary. This spring he is working with two UMD graduate students, Adam Moren and Kyle Thomsen, who both are using neutrino detector data in their masters degree thesis research.
HOW IT WORKS
Scientists generate a beam of the particles for the NOvA experiment using one of the world’s largest accelerators, located at the Department of Energy’s Fermi National Accelerator Laboratory near Chicago. They aim this beam in the direction of the two particle detectors, one near the source at Fermilab and the other in Ash River, Minn., near the Canadian border. The detector in Ash River is operated by the University of Minnesota under a cooperative agreement with the Department of Energy’s Office of Science.
Fermilab creates a beam of neutrinos by smashing protons into a graphite target, which releases a variety of particles. Scientists use magnets to steer the charged particles that emerge from the energy of the collision into a beam. Some of those particles decay into neutrinos, and the scientists filter the non-neutrinos from the beam. Billions of those particles are sent through the earth every two seconds, aimed at the massive detectors. Once the experiment is fully operational, scientists will catch a precious few each day.
Different types of neutrinos have different masses, but scientists do not know how these masses compare to one another. A goal of the NOvA experiment is to determine the order of the neutrino masses, known as the mass hierarchy, which will help scientists narrow their list of possible theories about how neutrinos work.
ASH RIVER'S ROLE
“The neutrinos from the Fermilab are also aimed at a third detector near the town of Tower in northern Minnesota,” Habig said. “They send out neutrinos in a pattern more like a flashlight than a laser beam, so at the Ash River detector we are quite literally looking at things from a different angle.” Habig said the neutrinos detected at Ash River are fewer in number but more precise.
Neutrinos are curious particles. They come in three types, called flavors, and change between them as they travel. The two detectors of the NOvA experiment are placed so far apart to give the neutrinos the time to oscillate from one flavor to another while traveling at nearly the speed of light. Even though only a fraction of the experiment’s larger detector, called the far detector, is fully built, filled with scintillator and wired with electronics at this point, the experiment has already used it to record signals from its first neutrinos. Once completed, NOvA’s near and far detectors will weigh 300 and 14,000 tons, respectively. Crews will put into place the last module of the far detector early this spring and will finish outfitting both detectors with electronics in the summer.
“This early result suggests that the NOvA collaboration will make important contributions to our knowledge of these particles in the not so distant future,” said University of Minnesota physicist Marvin Marshak, Ash River Laboratory director. Habig, who works closely with Marshak, is helping to manage the large data volume coming from this huge detector. His work, as he phrases it, is to determine, "At exactly which time should we fish for the needle in the data haystack?"
The NOvA experiment is scheduled to run for six years. Because neutrinos interact with matter so rarely, scientists expect to catch just about 5,000 neutrinos or antineutrinos during that time. Scientists can study the timing, direction and energy of the particles that interact in their detectors to determine whether they came from Fermilab or elsewhere.
The experiment receives funding from the U.S. Department of Energy, the National Science Foundation and other funding agencies.
Story by Cheryl Reitan. February, 2014.
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