Fermilab honors UC student for 'new physics' quest

Physicists at the University of Cincinnati are trying to understand why matter and antimatter weren’t destroyed in equal parts during the Big Bang.

The dominance of matter over antimatter is the reason we have atoms and molecules and hippopotamuses today. But it’s still a mystery that physicists such as UC postdoctoral fellow Jacob Todd are trying to unravel.

Todd was honored this month by two prestigious scientific organizations for his doctoral thesis on the search for new subatomic particles. The Universities Research Association, Inc., and U.S. national physics laboratory Fermilab selected Todd for its annual outstanding graduate thesis award. He was recognized at Fermilab's annual users conference.

Todd and his advisor, UC physics professor Alexandre Sousa, are part of an international team that published its experimental results in March in the prestigious Physical Review Letters, a journal of the American Physical Society.

The researchers are exploring neutrinos, the most abundant subatomic particle with mass in the known universe. Physicists have identified three kinds: electron neutrinos, muon neutrinos and tau neutrinos.

Physicists suspect there is a fourth, called a sterile neutrino. But experiments by Todd, Sousa and their research collaborators at Fermilab did not find them.

The collaboration demonstrates UC's commitment to research as part of its strategic direction called Next Lives Here.

At Fermilab, physicists fire a high-intensity neutrino beam at two detectors situated 1 kilometer and 735 kilometers away from the accelerator.

“You can think of it like the flashing of a laser — brief periods or events separated by a fraction of a second. On, off. On, off,” Todd said. “Then you time your detectors to look for those events based on the speed of travel. And they’re traveling at very close to the speed of light.”

The particle accelerator fires a beam of neutrinos in pulses every second, several thousand times per hour, every hour of every day for the past decade.

“We have people on the clock at 3 a.m. on Christmas morning,” Todd said. “That’s the dedication it takes.”

Physicists look for sterile neutrinos by observing the “disappearance” of muon neutrinos between the two detectors. Not all of the muon neutrinos observed in the near detector are observed in the far detector. Where did they go?

Well, some neutrinos change “flavor,” oscillating from muon neutrino to electron neutrino or back again during their transit. And physicists have theorized that some of the neutrinos they don’t find at the far detector might have oscillated into a yet-undiscovered type of neutrino: a sterile neutrino.

But UC’s physicists and their international colleagues did not find evidence of sterile neutrinos. The results are in conflict with a 2018 experiment called MiniBooNE that found significant evidence of sterile neutrinos.

There isn’t very much antimatter in the known universe, although physicists have created small amounts in particle accelerators like the one at Fermilab. Antimatter is produced by the sun when particles collide during solar flares and when cosmic rays strike the Earth’s upper atmosphere.

Oddly, bananas create antimatter as well. The decay of trace amounts of radioactive potassium releases subatomic particles called positrons — one about every 75 minutes.

“Bananas are slightly radioactive,” Todd said.

Neutrinos are particles you can actually observe yourself — sort of. YouTube is full of videos about making a cloud chamber. All it takes is a jar, a sponge soaked in rubbing alcohol, dry ice and a flashlight. The dry ice condenses the alcohol into a vapor or cloud. The subatomic particles zipping through space are betrayed by lines of condensation that look like contrails made by the world’s tiniest jets. But Sousa said it would take a stroke of luck to observe a neutrino in your cloud chamber since they so rarely interact with matter.

When matter and antimatter meet, they annihilate into pure energy.

“Imagine if two baseballs made of matter and antimatter collide,” Todd said. “You’d see a massive burst of heat and light. There wouldn’t be a single particle left. It would be the most efficient explosion you’ve ever seen.”

Featured image at top: UC postdoctoral fellow Jacob Todd. Photo/Joseph Fuqua II/UC Creative Services