Neutrinos are the second-most abundant particle in the universe after photons, and only about 400 physicists in the United States study these weakly interacting and difficult-to-detect particles.
“It’s probably safe to say that in the few years since the discovery of the Higgs Boson, we know more about the Higgs than we know about neutrinos after 50 years of research,” said Jon Link, associate professor of physics and director of the only Center for Neutrino Physics in the nation. “We’re not even sure how many there are. Three for certain, but there are clues for a fourth, a sterile neutrino, and that’s an exciting possibility.”
The Higgs, Link said, is the elementary particle responsible for the mass of all the other particles. It has been referred to as the "god particle" because of the importance of this function.
Virginia Tech researchers have led the search for the sterile neutrino for years. In the last two decades, there have been hints a sterile neutrino may exist, and those hints have increased the last few years, said Patrick Huber, associate professor of physics.
“Finding a fourth neutrino would be huge,” Huber said. “When looking for the Higgs, they knew it should exist. We don’t ‘know’ a fourth neutrino exists, and that makes it exciting. Finding it would open up a whole new area of physics.”
If it exists, it will be difficult to find because a sterile neutrino doesn’t interact with anything in the standard model of physics, except through its mixing with other neutrinos. Finding it could be the portal that leads to new areas of physics and answers to issues surrounding dark matter and why the universe is made of matter instead of anti-matter.
Where does one start looking? At the beginning. The very beginning.
“There were neutrinos created in the big bang, and there’s a great deal of excitement now from people looking at the light that was created in the big bang — a relic from 300,000 years after,” Link said. “From the very first second, neutrinos from the big bang started free-streaming. Today they are very, very low energy, and no one knows how to detect them yet. The person who figures it out almost certainly earns the Nobel Prize.”
The next question is how do scientists know these neutrinos even exist?
“They have to if the physics we understand right now is correct,” Huber said. “We can see vestiges in the cosmic microwave background and the large-scale structure of the galactic clusters. So we know they have to be there. We can measure how much energy was in the early universe, and that only works out if there were roughly three or maybe four neutrinos.”
For the most part, the neutrino is the particle science knows least about. That the neutrino has mass is certain, but what that mass is and why that mass is so small in relation to other particles are unknown.
“Neutrinos are fascinating because they carry enormous amounts of information — from the big bang to how stars explode,” Link said. “For instance, we still don’t know how stars explode. Computer simulations fail to realize an explosion, so neutrinos can perhaps help explain this.”
To get to these answers, Camillo Mariani, assistant professor of physics, is developing new methods to detect neutrino interactions. His work includes the evocatively named “liquid argon time projection chamber,” which will allow the detector to act as a high-accuracy imaging detector. “Neutrino research is very long term because of the costs involved and the scarcity of neutrino interactions to study,” Mariani said. “Proposed large detectors such as the Long Baseline Neutrino Experiment, is a $1 billion to $2 billion project that will take 10 years or more to build and then run for another 10 to 20 years.
Until such a time as the larger detectors get built, the Center for Neutrino Physics keeps working with existing detectors and refining them and methods of neutrino production that will hopefully provide additional insight into the elusive particle.
“Everybody in particle physics now is trying to find physics beyond the standard model. Neutrino mass is beyond the standard model, but it works with a simple extension,” Link said. “A fourth neutrino would really break the model. The center is planning future experiments with new detector and neutrino source technologies. That’s how we’re inventing the future.”
Operated by the Virginia Tech Department of Physics, Kimballton Underground Research Facility sits in a cavern near the bottom of a working limestone mine in Giles County, Virginia. Most experiments there focus on particle physics involving neutrinos and other subatomic particles.
The Western Virginia Water Authority provides water service to more than 158,000 people each day. For more than 10 years, Virginia Tech scientists and students have used an environmentally friendly approach to help to make sure the water is safe.