Neutrino Physics
Then: A Detector that Fits in a Pickup
Now: Detectors that Fill a Goldmine
Illustration of neutrinos bombarding the Earth.
Every second, Earth's surface is bombarded by tiny, invisible particles known as neutrinos, which originate from some of the most extreme events in the cosmos, including the Big Bang. Researchers like Mitchell Soderberg, professor and department chair of physics, utilize advanced particle detectors to study neutrino interactions.
Understanding these interactions could help scientists uncover why our Universe exists and why all the "stuff" in the Universe, including stars, planets, and people, is made of matter rather than antimatter. Soderberg discusses the progress made in neutrino research over the past 25 years and offers his perspectives on its future.
How has neutrino detection evolved over the last 25 years?
Mitchell Soderberg (MS): The development of Liquid Argon Time Projection Chambers (LArTPC) in the past 25 years has been a significant step forward in neutrino detection. These detectors were first proposed in the late 1970s and there was an extensive development campaign in Italy for several decades leading to the ICARUS experiment, but it was really only in the late 1990s and early 2000s that the technology started to mature.
As a postdoc at Yale University, I was fortunate to get to play a leading part in building the first LArTPC, called ArgoNeuT, in the United States to be exposed to a neutrino beam (and only the second in the world at that time to have ever collected neutrino data). The entire ArgoNeuT experiment (enclosing 0.25 tons of liquid argon) would very comfortably fit in our laboratory on the third floor of the Physics Building, but it collected neutrino data that helped galvanize the community to pursue the technology further.
Can you reflect on how the scope of projects have changed from earlier in your career to now?
(MS): Now we are pursuing the Deep Underground Neutrino Experiment (DUNE), which will feature multiple Physics-Building-sized LArTPCs (each enclosing around 10,000 tons of liquid argon) one mile deep in an abandoned gold mine in South Dakota. It’s amazing to compare ArgoNeuT, which at some point I loaded by hand into the back of my small GMC pick-up truck and drove across the Fermilab property to be installed, to DUNE, which involves >1000 scientists from around the globe all working together to deliver components to South Dakota that have to be lowered underground through a small elevator shaft and then carefully assembled. It’s the ultimate ship-in-a-bottle situation.
One of the massive caverns in South Dakota which will house DUNE detectors. (Credit: Matthew Kapust, Sanford Underground Research Facility)
Where do you predict the field will be by 2050?
(MS): Well, it was only around 25 years ago that the third “tau” flavor of neutrino expected in our best theory of the subatomic world, called the Standard Model, was experimentally discovered, and also around then that neutrino flavor oscillations were conclusively observed (work that received the Nobel Prize in 2015). Now, we take those things for granted.
I fully expect large experiments like DUNE or Hyper-Kamiokande will be very active and making exciting discoveries in the year 2050, but I also am hopeful that developments in detector instrumentation will allow innovative “tabletop”-sized methods to study these particles that is complementary to what the huge experiments provide.
What are some other reasons to be excited about the future of neutrino research?
(MS): I'm optimistic that in the next 25 years we’ll learn if there are connections between neutrinos and “dark matter”, or if neutrinos are a gateway to understanding other “new physics” phenomena beyond that expected by the Standard Model.
The recent Snowmass process (which is a sort of decadal pulse-check of what the research community is excited about and what should be prioritized) was the source of seemingly endless ideas for future directions in neutrino-related research. The field is as vibrant as ever and young scientists who are currently undergraduates and graduates at places like Syracuse University will be leading it 25 years from now.
With more advanced neutrino detectors set to come online in the coming years, what type of groundbreaking discoveries about the Universe might be on the horizon?
(MS): It’s very cliché to say this, but I think it’s always the unexpected discoveries that are the most exciting and potentially transformative. We definitely have scientific goals in mind with something as vast and complex as DUNE, like conclusively measuring whether neutrinos and antineutrinos behave in the same way or not (a thing we call “charge-parity symmetry”), and whether that might be part of the reason why our universe is dominated by matter and not antimatter. That would be an amazing, possibly Nobel-prize winning, discovery.
But we might also get lucky and see the neutrinos from a supernova in our galaxy and learn about the dynamics of exploding stars, or find ways to utilize the LArTPC technology that underpins DUNE to discover some unexpected new physics beyond that expected in the Standard Model. It can certainly be challenging to work with >1000 colleagues from around the globe and get them to agree on any one thing, but when you gather smart and creative people with diverse backgrounds and give them tools to explore with, they can make discoveries that change the way we understand the world around us.
