Mysterious Neutrino Particles May Hold Keys to Evolution of the Universe

Every second, a trillion neutrinos from the sun and other celestial objects pass through our bodies like we’re invisible. And while neutrinos are the most abundant subatomic particles with mass in the universe –– a billion times more than those that make up the planets, stars and humans –– they so rarely interact with other matter that they are poorly understood and tricky to detect.

As part of the Department of Energy’s Neutrinos at the Main Injector (NuMI) Off-Axis Electron Neutrino Appearance or (NOvA) Experiment, scientists can not only detect many of these neutrinos, but they are also confirming that the chameleon-like tiny particles can change form.

QUICK CHANGE ARTISTS

“For many years we had been able to detect the neutrinos, but back in 1998 they surprised us in terms of ultimately having a tiny amount of mass and more importantly, being able to change form –– technically called flavor –– from one type to another,” says Alexandre B. Sousa, University of Cincinnati assistant professor at the McMicken College of Arts and Sciences’ Department of Physics. “And understanding how this process works can tell us what their mass actually is, which is still a huge mystery.”

Knowing the neutrinos can change from one form, which scientists call "flavors," to another flavor can only be possible if they have a tiny mass. And Sousa explains that even though neutrinos have such a tiny mass –– much smaller than the particles that make up larger matter –– they must indeed have an impact on how the universe is evolving.

The ordering pattern of the neutrino masses is one of the major unknowns in neutrino physics, but Sousa says is critical in understanding the mechanism responsible for giving mass to the neutrinos. In parallel,

NOvA should be able to provide hints on whether neutrinos may have played a role in causing the small matter-antimatter imbalance in the early universe during the big bang, ultimately responsible for us being here to ask the question.

“Depending on their mass, the universe may expand forever, or at some point it may stop expanding altogether and just collapse back,” says Sousa. “So understanding the neutrino flavor change phenomenon will have a great impact.”

SCIENCE GOES UNDERGROUND

Less than a year after the official start of the NOvA experiment, the first results were announced in early August at the American Physical Society’s Division of Particles and Fields Conference in Ann Arbor, Michigan. Sousa, along with 210 scientists and engineers from 39 institutions recently verified that the experiment’s massive particle detector – 50 feet tall, 50 feet wide, and 200 feet long – is sitting in the sweet spot for detecting neutrinos fired from a 500-mile distance, from Fermilab in Illinois, to Ash River in northern Minnesota.

“Ultimately, the precise measurement of this particle conversion can have deep implications for why we are all here and why there is so much matter all over the universe, but we don’t see any antimatter,” says Sousa. “Neutrinos may actually help us explain this and provide the key to the evolution of the universe.”

This announcement also came only a week after many of those same scientists convened at the University of Cincinnati for a summer meeting of the NOvA Neutrino Experiment organized by Sousa and supported by the UC Physics Department and the McMicken College of Arts and Sciences. In the spirit of Cincinnati Smart, the goal was to bring in undergraduate and graduate students and physicists as possible to discuss and prepare the first results of the NOvA experiment, which was later shared with the public.

“We know neutrinos exist because the first ones were detected in 1956,” says Sousa. “But in the new NOvA experiment, we will detect thousands of these particles. And unlike the electron that will stay an electron until the end of time, we are seeing that neutrinos have these strange properties that enable them to change from one type to another.”

Sousa says he and other scientists are currently studying neutrinos at a fundamental level, but these fundamental understandings often lead to useful applications later. According to Sousa, one direct application of earlier neutrino studies concerns the recent international headlines about the negotiations the U.S. and Iran are trying to secure, which would include essential monitoring of Iran’s production of nuclear energy.

NOTICING NUCLEAR DECAY

When a nuclear reactor produces energy for civilian consumption, it will generate antineutrinos through radioactive decay, but when it is used to produce plutonium for an atomic bomb –– which is something people don’t want Iran to do –– Sousa explains that measuring those antineutrinos will provide tell-tale signs of that undesired activity.

“Monitoring of Iran’s nuclear reactors is an essential part of the Iran Nuclear Energy Deal,” says Sousa. “So placing neutrino detectors, which could be housed in buildings as small as an office, as close as possible to the nuclear reactor facility would be a way of checking to make sure Iran is not producing plutonium for atomic weapons, and also that any plutonium produced in normal civilian operation is not being stealthily removed from the reactor.”

Along with Adam Aurisano, UC post-doctoral fellow, Sousa has made leading contributions to the development and improvement of NOvA simulations. Having contributed to NOvA’s data analysis since 2008, Sousa currently serves as co-coordinator of the NOvA Detector Simulations working group. In particular, he says

they are looking at the particle’s role in the balance between matter and antimatter.

KEY FINDINGS

After some 12 years from concept to starting operations, and $300 million later, scientists on the NOvA experiment are confirming that the remarkable detector not only functions as planned, but has seen strong evidence of neutrinos converting from muon to electron flavor, and with more data, will potentially result in a quantum leap toward understanding the nature and behavior of the elusive particles.

“One of the positive keys to these NOvA results has been our ability to reject most cosmic rays that rain down from the atmosphere,” says Sousa. “We have managed to reject all but one in every 40 million cosmic rays from being included in the analysis, which is really remarkable. NOvA has proved that you can do neutrino experiments with detectors on the surface successfully, which can be much more cost effective.

“Where the other experiments like MINOS at Fermilab and T2K in Japan use underground detectors, NOvA has shown success operating on the surface.”

As NOvA sets out on its journey of scientific discovery, the success of its program critically hinges on its ability to simulate both the experimental apparatus and the neutrino physics being studied. And while this is a monumental task in itself, crunching the data is even more daunting, so Sousa has leveraged the Ohio Supercomputer Center (OSC) into providing a total of 600,000 CPU hours dedicated to the production of NOvA simulations.

SOUSA'S FUNDING:

• Department of Energy (DOE) base grant from the High Energy Physics program of the Office of Science. Three-year support (renewable) for PI and graduate student.
• ORAU Ralph J. Powe Junior Faculty Enhancement Award. One-year support between June 2014 and May 2015 for PI and undergraduate student to work on the Deep Underground Neutrino (DUNE) project.
• Fermilab Intensity Frontier Fellowship. Support between October 2013 and June 2014 to develop NOvA and MINOS+ research while in residence at Fermilab, and present results at the Neutrino 2014 international conference, which took place in Boston, MA, in June 2014.
• Ohio Supercomputer Center is providing a 600,000 CPU-Hour annual allocation dedicated to NOvA computing needs.?
• For their summer Quarknet program, Sousa and Mike Sokoloff, a Professor of Physics, receive funding from the NSF via a University of Notre Dame sub-contract.
  

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information.

For more information, visit the experiment’s website. Watch live particle events recorded by the NOvA experiment online. Follow the experiment on Facebook and Twitter.

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. The Fermilab Accelerator Complex is an Office of Science user facility.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC. Visit Fermilab’s website, and follow Fermilab on Twitter at @Fermilab.

The Ohio Supercomputer Center (OSC), a member of the Ohio Technology Consortium of the Ohio Board of Regents, addresses the rising computational demands of academic and industrial research communities by providing a robust shared infrastructure and proven expertise in advanced modeling, simulation and analysis. For more, visit www.osc.edu.

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