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NOvA Experiment Sees First Long-Distance Neutrinos

Source: Fermilab Today, February 11, 2014

Scientists on the world’s longest-distance neutrino experiment announced today that they have seen their first neutrinos.

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.

“NOvA represents a new generation of neutrino experiments,” said Fermilab Director Nigel Lockyer. “We are proud to reach this important milestone on our way to learning more about these fundamental particles.”

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.

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.

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.

“That the first neutrinos have been detected even before the NOvA far detector installation is complete is a real tribute to everyone involved. That includes the staff at Fermilab, Ash River Lab and the University of Minnesota module facility, the NOvA scientists, and all of the professionals and students building this detector,” said University of Minnesota physicist Marvin Marshak, Ash River Laboratory director. “This early result suggests that the NOvA collaboration will make important contributions to our knowledge of these particles in the not so distant future.”

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.

“The first neutrinos mean we’re on our way,” said Harvard physicist Gary Feldman, who has been a co-leader of the experiment from the beginning. “We started meeting more than 10 years ago to discuss how to design this experiment, so we are eager to get under way.”

The NOvA collaboration is made up of 208 scientists from 38 institutions in the United States, Brazil, the Czech Republic, Greece, India, Russia and the United Kingdom. The experiment receives funding from the U.S. Department of Energy, the National Science Foundation and other funding agencies.

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.

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.

Fermilab started sending a beam of neutrinos through the detectors in September, after 16 months of work by about 300 people to upgrade the lab’s accelerator complex.

“It is great to see the first neutrinos from the upgraded complex,” said Fermilab physicist Paul Derwent, who led the accelerator upgrade project. “It is the culmination of a lot of hard work to get the program up and running again.”

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.

“Seeing neutrinos in the first modules of the detector in Minnesota is a major milestone,” said Fermilab physicist Rick Tesarek, deputy project leader for NOvA. “Now we can start doing physics.”

Note: NOvA stands for NuMI Off-Axis Electron Neutrino Appearance. NuMI is itself an acronym, standing for Neutrinos from the Main Injector, Fermilab’s flagship accelerator.

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Data collected at the NOvA far detector in northern Minnesota shows one of the first interactions captured at that detector from a beam of man-made neutrinos. The neutrino beam is generated at Fermilab in Illinois and then sent through 500 miles of earth to the far detector. Image courtesy of NOvA collaboration.. (1 of 11)
A graphic representation of one of the first neutrino interactions captured at the NOvA far detector in northern Minnesota. The dotted red line represents the neutrino beam, generated at Fermilab in Illinois and sent through 500 miles of earth to the far detector. The image on the left is a simplified 3-D view of the detector, the top right view shows the interaction from the top of the detector, and the bottom right view shows the interaction from the side of the detector. Illustration courtesy of Fermilab. (2 of 11)
Scientists and engineers at Fermi National Accelerator Laboratory developed the 750,000-pound pivoter machine that put the blocks of the NOvA detector in place. Photo by Fermilab. (3 of 11)
The NOvA detector, currently under construction in Ash River, Minn., stands about 50 feet tall and 50 feet wide. The completed detector will weigh 14,000 tons. Photo by Fermilab. (4 of 11)
Technicians glue modules for the NOvA detector using a machine developed at Argonne National Laboratory. Photo by William Miller, NOvA installation manager. (5 of 11)
Electronics that make up part of the data acquisition system are installed on the top and side of the detector. The NOvA experiment is a collaboration of 208 scientists from 22 universities and laboratories in the United States and another 16 institutions around the world. The scientists are funded by the U.S. Department of Energy, the National Science Foundation and funding agencies in the Czech Republic, Greece, India, Russia and the United Kingdom. Photo by Fermilab. (6 of 11)
A view of the top of the nearly completed NOvA far detector in northern Minnesota. The detector is made up of 28 PVC blocks, each weighing 417,000 pounds, and spans 51 feet by 51 feet by 200 feet. When it is completed and filled with liquid scintillator, the far detector will weigh 14,000 tons. Photo courtesy of NOvA collaboration. (7 of 11)
Workers at the NOvA hall in northern Minnesota assemble the final block of the far detector in early February 2014. The project is a collaboration with the University of Minnesota, and roughly 170 students built the modules that make up the far-detector blocks. Photo courtesy of NOvA collaboration. (8 of 11)
Workers at the NOvA hall in northern Minnesota assemble the final block of the far detector in early February 2014, with the nearly completed detector in the background. Each block of the detector measures about 50 feet by 50 feet by 6 feet and is made up of 384 plastic PVC modules, assembled flat on a massive pivoting machine. Photo courtesy of NOvA collaboration. (9 of 11)
The NOvA detector, located in Ash River, Minn., will study a beam of neutrinos originating 500 miles away at Fermi National Accelerator Laboratory, located near Chicago. Image by Fermilab. (10 of 11)
When completed, the NOvA detector will comprise 28 detector blocks, each measuring about 50 feet tall, 50 feet wide and 6 feet deep. Photo by Fermilab. (11 of 11)