A Scrappy Approach to Experimental Physics

Duke faculty member Phil Barbeau is associate professor of physics. He’s an experimental nuclear and particle physicist who builds things in his quest to understand what makes up matter, at the very deepest level, and how the universe behaves.

“Our group is kind of plucky,” he says. “We do things with our friends and collaborators that many think cannot be done, and some think should not be done. We look for sort of invisible stuff.”

We caught up with Barbeau to ask a few questions about his research and training of graduate students (“teaching them how to do physics the way I like to do it is extremely rewarding”). Below are excerpts from the conversation.

How He Came to Love Physics

My parents were both chemists. We would drive around and they’d say [something like], the whole world is made up of sand or smaller bits, and then eventually you get to molecules. I used to walk around with this idea in my head — I was nine or ten — that I knew a secret that no one else knew, which was that the universe was made out of small bits of things, of molecules, and those things were made of atoms.

As a kid, I thought, OK, that’s it, but then it sort of bothered me that, well, what if you just keep going? What’s the next level down? And so in high school chemistry, you learn about electrons and protons and maybe neutrons, because you’re learning about the periodic table.

But this bothered me too, because what if you keep going beyond that? What’s smaller?

I stumbled upon something called quarks. Three quarks make up a neutron or a proton. […] I got down to this understanding that there’s really only about a dozen fundamental things out there. All of the complexity of the world we live in grows out of that, and that was really magical to me.

So I got into nuclear physics and particle physics.

Looking for the Impossible Things

Now, what I get a lot of joy out of is looking for the impossible things, the really hard problems. What we do [in our lab] is look for impossible-to-detect particles, or phenomena or processes or interactions, that could [lead us to] interesting questions about the big world outside.

One of those questions is the search for something called dark matter.

If we measure the mass of all the stars by looking at how much light there is, and then measure the mass of the stars by looking at the dynamics of how these things are moving, they don’t agree. So there’s something out there that’s dark, that’s not lighting up, but that is massive. This is called dark matter.

And so maybe there’s physics beyond the standard model — there’s another particle that’s impossible to see. It’s out there in space, going through us all the time, and it’s making up this dark matter, so maybe we should look for it.

Another question that we have is about a particle called the neutrino. It’s very weird, and numerous times over the past 25 years, it’s defied our expectations. Neutrinos are a window, possibly, into this search for a physics beyond the standard model.

One of the ways in which we look for neutrinos is at a facility in Oak Ridge, Tennessee, called the Spallation Neutron Source. We think it’s the most sensitive way to look for deviations from the standard model. We look for what used to be an impossible-to-detect interaction, something called coherent neutrino scattering.

So that’s the kind of research I do. I build detectors to look for these things, and I tinker. It’s a lot of scrounging for things, really pushing the limits of technology, trying to answer these questions.

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Mentorship

One of the things that’s really important to me is mentorship. I have a relatively large group of graduate students, and teaching them how to do physics the way I like to do it is extremely rewarding. We do it in a very particular style. It’s very scrappy. It’s very MacGyver style, very junkyard style.

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They come out of here having seen the full life cycle and spectrum of what it takes to build neutrino experiments, from designing them to conceptualizing them to finishing them off. Several times, students have done many neutrino experiments and they’ve become leaders in the field. It’s really exciting to see.

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And the contrast to many other types of neutrino experiments or similar experiments in the dark matter field is that you might have many, many people working on one experiment and every seven to ten years, it might produce a result. But here, a student can show up, design an experiment, deploy it, measure it, finish the analysis in a reasonable time in a Ph.D., and oftentimes be part of another one or two other detectors.

Summer Plans

This summer is going to be the deployment of several new detectors in Oak Ridge. Neutrino detectors are typically huge, but we build really small-scale ones that fit on the side of the wall in this very thin, narrow hallway, six feet wide, which we call Neutrino Alley. We’re very good at building very sensitive detectors that are very small.

So we’re deploying a number of experiments, and we're finishing up the analysis of some data that we took over the last six months. That’s extremely exciting, and it’s the most sensitive version of this measurement yet.

Main image, above: “Our group decided to dress up as me for Halloween,” said Phil Barbeau. Left to right: Tyler Johnson, Isabel Colon-Rivera, Charlie Prior, Natalie Jones, Barbeau, Emma van Nieuwenhuizen and Jay Runge.

Aitor Bracho poses next to his experiment measuring fission product yields, to try to understand the spectrum of neutrinos from nuclear reactors. (Photo: The Graduate School)

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Emma van Nieuwenhuizen poses inside the Tandem Van de Graaff accelerator at the Triangle Universities Nuclear Laboratory (TUNL), on Duke’s campus. The group uses the accelerator to calibrate neutrino detectors.

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Anna Torres demonstrates her undergraduate project aimed at 3D imaging, which the group uses for understanding detector positions in its calibration experiments.

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Phil Barbeau installs a detector to be calibrated, at the center of an array of “backing detectors” at the Tandem Van de Graaff. 

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