The Race For Universal Under(ground)standing Of The Neutrino

May 17, 2018

Vincente Guiseppe points to an extra 6-layer shield, which is what the Majorana Demonstrator looks like on the inside.
Credit Lee Strubinger / SDPB

Researchers with the Majorana Demonstrator Collaboration have proven they can create an environment that  lets them see what’s called neutrino-less double beta decay.

Lingo aside, it’s a reaction that researchers say may help explain why matter exists.

The Yates is one of two shafts from the Homestake Mine that takes researchers down 4,850 feet.

The shaft  is built from  timber beams  that roll past on the way down . Water drips down the shaft to keep the wood from drying out, . No matter how bright and sunny it is outside, the dark and damp ride underground is gloomy at best, like standing in the rain. At the bottom of  this  10-minute ride  some of the world’s top scientists are chasing for origins of the universe.

To reach that understanding, scientists needed to  to design, grow and build a piece of equipment called the Majorana Demonstrator, to create a low energy environment. The demonstrator is a 6-layer shield of everything from polyethylene plastic to the world’s purest copper. Inside are  cryostats full of an element called germanium… All of this is needed to observe a very sensitive process called “neutrino-less double beta decay.” Observing that process would tell scientists only one thing…

“To explain why we’re here, why there’s matter in the universe," says Cabot-Ann Christofferson, a liaison between the experiment and Sanford Lab.

Earlier this year, researchers created an environment free from background interference to potentially observe the decay process in the element germanium.

Christofferson says observing this process in a normal environment is like trying to hear one voice in  a crowded room.

“Eliminate all the other things that are making noise, then you can hone in on the one thing you’re trying to listen to, or in this case observe,” Christofferson says. “Eliminating the background from the material surrounding the germanium is the key, so we can focus in on the actual noise the germanium would make, or the signal the germanium is making.”

Just outside the Majorana Demonstrator Collaboration Class 100 clean room.
Credit Lee Strubinger / SDPB

Just to reach this point took eight years, and required what’s called a Class-100 clean room, an immaculate, filtered environment. Researchers must wear Tyvek suits to protect the experiment from any oils and particles on human skin. Any cell phones and glasses must be wiped clean with alcohol towelettes.

It’s a lot of effort, but what these  researchers are hoping to observe is very, very rare. Neutrinos are everywhere, trillions pass through us at any given second. They’re subatomic particles produced by fusion reactions inside stars. However, here researchers are on the hunt for a reaction that does not  produce a neutrino.

Vincente Guiseppe is also a spokesperson with the  Project. He says observing a reaction without a neutrino tells them something special about properties of the neutrino.

“That it allowed that process to take place, even without it there in the end. That means it’s acting in a way that doesn’t make sense, given our standard way of looking a physics and particle physics. If that were to be true, it tells us the neutrino is acting in a new way we believe could happen, but we haven’t observed it," Guiseppe says. "It’s telling us about some balances in Nature that don’t add up the way we thought. We thought every time you have one type of particle you have another particle to balance it. In this case the electron is balance by a neutrino.”

Guiseppe says if a neutrino is not there following a reaction, that tells researchers something they didn’t know about the universe -- that there can be an imbalance of particles.

“In the beginning of the universe there should have been equal parts matter and anti-matter,” Guiseppe says. “We look around, I see you, I see the building, I see the stars, I see the sun… that’s all matter. Yet, all the matter should have annihilated, or canceled each other out. But after all that cancellation in the early universe, a tiny spec of matter was left over, and that tiny spec is everything we see.”

Observing a reaction without a neutrino  is a lot like winning the lottery. Phase two of this project will quadruple in size and take place in an underground lab in Italy. Currently, the demonstrator uses 44 kilograms of pure germanium to detect any of this special decay. Phase two will require  200 kilograms of germanium and start in several years.  Phase three will be even larger. Guiseppe says the larger the project, the more chances they’ll observe the phenomenon.

“If it’s behaving in all the ways we think it’s behaving this would be a really exciting thing to see. It would be an exciting decay to see, because it would show us… it would almost be—maybe not the final act—but you could imagine it being the final act of the neutrino,” Guiseppe says. “This is the climax of its story. We’ve explained a lot of how it acts, but now we find out it’s indistinguishable from its anti-partner. It can allow this sort of decay that we’re looking for to happen. This is something you could imagine being the final act of the play and this is going to get the most applause."

A 5-minute underground trolley ride away at the bottom of another mine shaft, a team of researchers will work on what’s call the Deep Underground Neutrino Experiment, or DUNE. Scientists will shoot a beam of neutrinos from Fermilab in Batavia, Illinois, 800 miles through the earth to detectors at the Sanford Lab.
 
The goal is to understand how neutrinos behave overtime. That’s tricky when your subject matter travels at the speed of light.
 
Debrah Harris is a senior scientist with Fermilab.
 
“The problem is that if something is going very close to the speed of light, or basically at the speed of light, if you want to wait a certain amount of time, you have to go a very long distance,” Harris says. “The only way to have two detectors that are both on the earth is to make a beam of neutrinos and shoot them through the earth and they will come out, back out the surface of the earth some long distance away.”
 
As neutrinos pass through the universe they oscillate in patterns. Harris, along with other scientists want to measure the moment a neutrino changes its oscillation, or flavor. Harris says that’s a key measurement.
 
“We have this new theory that neutrinos have mass and there’s some equations that govern their behavior that would tell you they should change energy, they should change flavors as a function of energy in a very specific way,” Harris says.
 
Harris says their work is unique because it’s measuring that change. But before any of those measurements can take place, they must build an underground lab. They’ll move 800-thousand tons of rock to make room for three caverns deep underground. Two of those three will contain huge cryostats full of liquid argon. In total, those cryostats will measure the equivalent of 20-olympic-size swimming pools. The remaining cavern will hold the equipment necessary to support the work.
 

Credit Lee Strubinger / SDPB

Chris Mossey is the deputy director for Fermilab, and is leading cosntruction of the facility that will house DUNE.

“Because of the nature of the work, and some of the engineering challenges, building these large cryostats underground is a bit like a ship in a bottle type of challenge,” Mossey says.
 
Mossey says he expects their project to be completed in eight years. Until then, they’ll need to focus on building a facility that lets them unlock the mysteries of the neutrino.