Science & Tech

Looking for subatomic insights in Minnesota

4 min read

After years of planning, officials broke ground this month for a new high-energy physics experiment that will probe the behavior of one of the basic particles that make up the universe: the neutrino.

The $278 million NOνA project, whose construction was jump-started with federal stimulus dollars, is run by the Fermi National Accelerator Laboratory in Batavia, Ill., and involves 181 investigators from 26 institutions, including Harvard.

Gary Feldman, the Frank B. Baird Jr. Professor of Science, heads a Harvard team including engineers, fellows, and students that is designing and building key electronics boards — 12,000 of them. The boards, which need to be cooled to minus 15 degrees Celsius, convert a light signal given off when a neutrino hits the detector into a digital signal that can be recorded and analyzed. Feldman also serves as co-spokesman for the project.

“This is the primary U.S. high-energy accelerator experiment for the next decade,” Feldman said. “We’re trying to measure some of the most fundamental parameters of physics.”

NOνA builds on an earlier project at Fermilab called MINOS and will use the same neutrino beam. The experiment consists of two detectors hundreds of kilometers apart. The near detector, located a kilometer from Fermilab, will provide a baseline measurement of the neutrinos in the beam. The far detector is located 810 kilometers away near the northern Minnesota town of Ash River, and will measure how the beam has changed as it traveled there. The project’s name is an acronym within an acronym. NOνA stands for “NuMI Off-Axis Electron Neutrino Appearance Experiment,” while NuMI is a reference to the neutrino beam and stands for “Neutrinos at the Main Injector.”

There are three different kinds of neutrinos among the 12 elementary particles that are the most basic building blocks of the universe. Two of the three kinds, the muon neutrino and the electron neutrino, are the primary subject of the NOνA experiment. Physicists have previously observed that the different neutrinos are able to change into each other. The rarest of these conversions is that of the muon neutrino into the electron neutrino through a process called oscillation. NOνA has been designed to study this phenomenon.

“We have discovered over the past decade that neutrinos will oscillate into each other over time,” Feldman said.

In addition to the behavior of neutrinos, NOνA may shed light on a basic phenomenon called the “CP violation.” In physics, every type of particle is expected to have an antiparticle: an electron has an antielectron, called a positron, for example. At the birth of the universe in the Big Bang, it is thought that an equal number of particles and antiparticles were created. However, in the world around us, antiparticles are rare, which is likely a consequence of CP violation in the first instants of the universe.

Neutrinos are small and extremely fast, traveling close to the speed of light. Since they can easily pass through the entire Earth, they are also difficult to detect. The May 1 groundbreaking was for the experiment’s far detector, which will be built over the next three years in a large pit near Ash River that will be then covered with earth. The near detector, much smaller, will be built over the next year.

The far detector is made up of 385,000 plastic tubes filled with scintillating mineral oil. It will stand five stories high, have an equal width, and run three-quarters the length of a football field. The first measurements are expected from the equipment in 2012.

Feldman spoke at the groundbreaking along with two U.S. congressmen, the president of the University of Minnesota, which is hosting the facility, and officials from the Department of Energy and Fermilab. Feldman said later that after years of ups and downs — the project was zeroed out in the federal fiscal 2008 budget — it is a relief to see it moving forward.

“It was very gratifying to see it get off the ground,” Feldman said.