Searching Where the Light is Shining: Professor Gabriel Orebi Gann

Professor Gabriel Orebi Gann in her lab (Photo by Johnny Gan Chong)

September 3, 2024
Avi Rosenzweig

Particle physics research is spinning its wheels, trying to gain traction on a very basic problem. Thirteen billion years ago, the Big Bang produced equal amounts of matter and antimatter. Theory holds that every particle has an antimatter companion that is virtually identical to itself, but with the opposite charge. But there are a lot more ‘ordinary’ particles than antiparticles – you reading this right now is clear evidence – so where is all the missing antimatter?

Theoretical physicists float a bunch of possible explanations for this slippage. Maybe it would be better to actually go and look at what is going on, no? Associate Professor Gabriel Orebi Gann is an experimentalist doing exactly that. Searching for clues is very difficult, but strongly preferable to speculating about the dimensions of an imagined castle in the sky. As Professor Orebi Gann emphasizes, “just because a model is self-consistent doesn’t mean it’s accurate.” Her detective work will provide the foundation for theoretical advances that make our understanding of the universe’s history more concrete and our predictions about its future more precise.

Rebelling in her own small way as a teenager, Gabriel Orebi Gann headed to Cambridge for college, when her family had a long connection with Oxford. First-years in natural sciences at Cambridge get to try out several subjects before settling into a major, and she took full advantage: mathematics, physics, chemistry, even a foray into biology before deciding better and changing to computer science. Just what someone who was not ready to commit needed at their start. Within each course, Orebi Gann showed a penchant for analysis that underpinned her burgeoning academic career. When it came time for grad school, the physicist didn’t fall far from the family tree, and she went to Oxford, like her father, earning a doctorate in particle and nuclear physics.

During postdoctoral research at Penn, Orebi Gann got involved with neutrino detection, and she’s been on that chase now for over a decade. Physicists are confident that understanding neutrinos is key to many of the major puzzles we have been hearing about: why supernovae explode, how heat is produced within the earth, the antimatter deficit, what’s going on in our sun, and more. Neutrinos are extremely difficult to detect: they are a billionth the size of protons; they move at almost the speed of light; they hardly interact at all with other particles; they are nearly massless.

Professor Orebi Gann in her lab (Photo by Johnny Gan Chong)

Until recently the way scientists caught a glimpse of neutrinos was by building huge tanks of heavy water inside former underground mines kilometers below the surface, and then recording the wakes that neutrinos make as they zoom through the tank. This is called Cherenkov detection. Orebi Gann worked at a Canadian project, the Sudbury Neutrino Observatory or SNO, where these studies determined that neutrinos were not quite massless – that discovery won the 2015 Nobel Prize in Physics for Arthur McDonald. That work provided the final proof that neutrinos have mass, a surprising finding that reshaped our understanding of particle physics. It means that neutrinos may be their own antiparticle. If so, then what we said above about every particle having a matching antiparticle might not be right—and how physicists add up what makes up the universe would need a major revision.

The newer way to get a look at these particles involves watching the photons that pop out of a material as it relaxes after being excited by passing neutrinos, called scintillator detection. This is much more sensitive than the Cherenkov method, and takes a smaller tank, too. The trouble is that such sensitive instruments require a lot of shielding, and can generate a lot of false hits when there is anything in the equipment that makes any noise. 

Professor Orebi Gann has used both Cherenkov and scintillator detection in her experiments. The innovation she is currently pursuing is to do both in the same tank. It’s more efficient and it yields better data. A win-win. Her lab group recently installed a small tank on the north side of campus in basement space owned by the Nuclear Engineering Department.. It’s a proof-of-concept setup called Eos that will set the new standard for how much useful data you can get out of this type of instrument. 

This project is getting some financial support from the U.S. Dept. of Defense because this technology could be sensitive enough to see emissions coming from nuclear energy plants and nuclear weapons factories, which could help with monitoring developments all over the earth (and perhaps eventually beyond it).

When she started her studies, Professor Orebi Gann had a talent for analysis and didn’t anticipate becoming an innovative instrumentalist. Her close collaborations are now with engineers more than with pure theoreticians, yet she generates the results that theoreticians need to be able to check their models. The joy she takes in managing a close team and solving problems together puts her less in the Oppenheimer mold than the Lawrence camp. Examining low-energy phenomena strains the patience and challenges the inventiveness of all investigators. Orebi Gann is certain that her team’s work will help physicists get “multiple handles” on these ghost-like particles that are especially tough to hold up to the light. Ones that don’t come with handles already attached. 

When Professor Orebi Gann started at Cambridge in natural sciences, gender diversity was not much of an issue, but as she progressed into studying particle physics the change in class composition was immediately evident. She was often the only girl in the classroom. She recalls perhaps one female instructor in her program. That experience has prompted her to the strong conviction that everyone should feel they can pursue whatever subjects interest them. Personal characteristics shouldn’t matter. Gender bias is still a problem today in smaller schools where there are very few women majoring in physics. Orebi Gann is of a temperament and background where she “never thought of myself as a woman in physics” but sees that many young women still need the encouragement and mentoring support that can be built into an institution and brought alive by caring faculty. She has established ties with other campuses, like CSUEB, to set up teaching and mentoring opportunities for UC Berkeley postdocs that can deliver the support that undergraduates need while relieving the overworked and understaffed science departments at CSUs from important roles they don’t have the capacity to provide. She is directing a new leadership program called “Shining Lights”  that starts in 2025. The program will combine gender diversity efforts with research training. 

Is the relation between theoretical physicists and experimentalists a chicken-and-egg situation? Maybe so – you need some idea of what you are looking for before you can build a machine to detect it; you also must have some way of deciding if your assumptions about how (nearly) invisible phenomena fit together are true. Gabriel Orebi Gann exemplifies the spirit of science through her emphasis on generating the experimental results that make theories testable. The old story about the drunk who is searching for his lost keys under the streetlight even though he dropped them in the park because ‘this is where the light is’ falls apart under the intensity and ingenuity of Professor Orebi Gann’s research—it will be what we find under her lights that produces the missing keys to open our understanding of nature.

  • The International Committee for Future Accelerators (ICFA) has announced that Orebi Gann is a recipient of the 2024 ICFA Instrumentation Awards. Orebi Gann has received an Early Career Award "For pioneering and developing an innovative detector technique to achieve a clear separation between scintillation and Cherenkov photons which has the potential to significantly influence the design of future neutrino experiments."

(Photo by Johnny Gan Chong)

Learn more about Professor Orebi Gann's research:

Tests begin on sensitive neutrino detector for nonproliferation as well as physics

March 15, 2024

Neutrinos and antineutrinos are nearly massless particles produced in many nuclear reactions, including the fission of uranium in nuclear power plants on Earth and the fusion reactions at the core of the sun.

But they are devilishly hard to detect — most pass through Earth without...Read more about Tests begin on sensitive neutrino detector for nonproliferation as well as physics

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