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A physicist and her neutrinos

MIT senior Christie Chiu has found her focus: the study of tiny particles.
Christie Chiu is currently working with physics professor Janet Conrad on research related to neutrinos
Christie Chiu is currently working with physics professor Janet Conrad on research related to neutrinos
Photo: Allegra Boverman
Photo: Allegra Boverman

Quarks, bosons, muons, electrons, neutrinos: This is the stuff the universe is made of, and these particles fascinate MIT senior Christie Chiu.

A physics and math major from Bedford, Mass., Chiu excelled in math and science from an early age and dreamed of attending MIT, her father’s alma mater. She and her best friend throughout grade school “would tell all our teachers — any adults, literally anyone who would listen — that when we grew up, we were going to become engineers, go to MIT, and be roommates,” Chiu recounts.

In middle school and high school, Chiu’s interest in MIT grew when she attended Splash, an annual, weekend-long program at the Institute packed with classes taught by MIT students. “I really liked the atmosphere, the energy that was here,” Chiu says.

As a freshman at the Institute, she found herself drawn to the physics department. “The professors were just so engaged in what they were teaching,” Chiu says. “I felt a lot of energy in the classrooms.”

Now, Chiu channels that same energy as a teaching assistant for Junior Lab, the notoriously challenging lab class for physics majors. “I absolutely fell in love with it, while other people were maybe not liking it so much,” Chiu says. “That’s one of the reasons I became a TA — so that I could get people more excited about this and make them want to go into experimental physics.”

Her efforts as a fervent ambassador for the Department of Physics have also included work as a counselor for PhysPOP, the department’s pre-orientation program for incoming freshmen. “It’s like summer camp for a week,” she says, smiling. “You get to play with all the cool things in the physics department at MIT!”

When she’s not busy with physics-related activities, Chiu spends time with her sorority sisters in Kappa Alpha Theta and captains the MIT sport pistol team, which she describes as a surprisingly meditative activity. “There’s a lot of mental focus and composure that’s required to excel in the sport,” she says.

Neutrinos in the spotlight

Chiu is currently working with physics professor Janet Conrad on research related to neutrinos: tiny particles, primarily produced in the sun, that constantly shower down upon the Earth.

Physicists have learned that these particles continually oscillate, or transform, among three types: electron, muon and tau neutrinos. To better understand this neutrino oscillation, researchers at the Fermi National Accelerator Laboratory, in Illinois, are conducting an experiment called MicroBooNE (Micro-scale Booster Neutrino Experiment). They use accelerators to generate a beam of neutrinos that then pass through very cold liquid argon, exciting some of the argon atoms. When the atoms return to a lower-energy state, they emit photons called “scintillation light” — which can give researchers valuable information about those neutrinos and their oscillations, helping to resolve discrepancies among the results from various neutrino experiments.

But that scintillation light has a wavelength of around 128 nanometers — which might as well be invisible. “It’s in the vacuum UV; it can’t even pass through glass,” Chiu says. “So that makes it very difficult for us to detect it.”

A chemical called tetraphenyl butadine, or TPB, provides a solution to the problem. When the scintillation light hits TPB, it is absorbed and re-emitted as blue light, at a longer wavelength of 425 nanometers — which can easily be detected. The only problem was that TPB seemed to stop working well after a while: For some reason, it degraded over time.

Chiu’s lab bench is surrounded by piles of acrylic plates, some clear and some with a milky coating of TPB. “We found that if we just left these laying out, then over time, the amount of light that it would be able to wavelength-shift went down,” Chiu explains. “We thought there might be effects from humidity, light or heat.”

Chiu’s research during her junior year finally identified the culprit: It was indeed light — specifically, the ultraviolet rays from sunlight streaming in through the large windows along one wall of the lab and from the overhead lights. Both are now covered with shielding material, allowing the TPB — and the researchers — to work uninhibited.

Last summer, Chiu presented the results of her TPB study at Fermilab alongside graduate students and postdocs from all over the country — and received first-place recognition for her research and poster.

New challenges

Now that Chiu has finished her work with TPB, she’s working on computer-generated simulations of neutrinos in liquid argon for MicroBooNE. The scintillation light that researchers detect is actually produced through two different microscopic processes, she explains. “Knowing the breakdown of how the light is produced between these two processes actually helps us identify the particle,” Chiu says. “We want to simulate the processes to verify that we fully understand the system.”

After graduating this spring, Chiu plans to pursue a PhD in particle physics and hopes to one day combine her love of research and teaching as a professor.

“There are still a lot of unanswered questions in particle physics,” Chiu says. “Believe it or not, the particles most people are familiar with — that is, protons, neutrons and electrons — compose very little of all the matter in the universe. There are so many things we don’t understand, like dark matter and dark energy, not to mention much about the elementary particles themselves. To learn more about these things — that’s what these experiments are here for.”

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