Neutrino beams, cosmic rays, and the origins of the universe

Why is the world around us made of solid matter when prevailing theories of physics predict an equal amount of antimatter? What can neutrinos, the mysterious particles that pass through our bodies in the trillions every second, tell us about the history and future of the universe? These questions lie at the heart of the planned Deep Underground Neutrino Experiment (DUNE), a major international collaboration being hosted by Illinois physics research center Fermilab.

Over the next few months, Doggerel will explore the project and the complex being built to house it, the Long-Baseline Neutrino Facility. To better understand what the project hopes to accomplish, we spoke with Steve Brice, deputy head of Fermilab’s neutrino division.


What is DUNE, and why is it important?

DUNE is a very large particle physics experiment. It’s going to study the properties of neutrinos by seeing how they transform as they travel from the creation point at Fermilab in Illinois to Sanford Underground Research Facility in South Dakota, which is 1,300 km [808 miles] away.

Why do you need such a long distance?

As a beam of neutrinos propagates over a long distance, it changes its characteristics. By propagating neutrinos through matter we can access properties that we haven’t previously been able to study. We’ve done these kinds of experiments before, but never at this long of a distance.

What do you hope to find?

One of the things we’re looking for is what we call CP [charge parity] violation, which really just means matter behaving differently from antimatter. We believe that for every matter particle there’s a corresponding antimatter particle. With a couple of technical caveats, matter should basically behave the same as antimatter. However, the world around us is full of matter. It seems that all of the antimatter has just vanished, which is one of the mysteries of physics: Where has all the antimatter gone?

It seems that all of the antimatter has just vanished.

One possibility is that matter and antimatter do behave differently. One of the things that we can do in this kind of neutrino experiment that we can do in very few other places is actually search for neutrinos behaving differently to antineutrinos. This may then provide a hint as to why the universe that we see around us is all matter and not a mix of matter and antimatter.

And why do you need to build a mile underground?

These large detectors are very, very sensitive. The surface of the earth is constantly bathed in a flux of cosmic rays, which would completely drown out the signals we’re looking for if the detectors were placed there. When we put these detectors deep underground, all that dirt shields out the cosmic rays but does nothing to the neutrinos.

What are the precedents for this project?

There have been smaller versions in the past. We’ve done it here; there’s a similar project in Japan; there has been a similar project in Europe.

Three things are very different about DUNE. One is the distance, 1,300km — no one’s done a neutrino experiment over such a long distance before.

No one’s done a neutrino experiment over such a long distance before.

Another is the new detector technology we’re developing to detect the neutrinos. It’s known as a liquid argon TPC, where TPC stands for time projection chamber. It basically enables us to take a photograph of the neutrino interaction and what comes out of that interaction. It also enables us to build incredibly massive detectors on a reasonable economic scale.

The third differentiator is the power of the beam. The beam of neutrinos that we’re going to send from Fermilab is two times as powerful as anything beamed before.


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