The physics major produced theoretical calculations for his thesis to chart possible results of particle collisions.

Building on research he conducted at Wayne State University in Detroit, Mich., last summer, Ching Li brought his thesis to a subatomic level. The physics major and math minor’s capstone project, “Theoretical Calculations of Cross Section and Asymmetry of Charged Lepton Flavor Violation Using an Effective Field Theory Approach,” examined charged lepton flavor violation (CLVF), a process that has never been observed experimentally.

When electrons and positrons (particles with the same mass but opposite charge) collide, they can produce tau-antitau or muon-antimuon pairs, which are made up of particles that are heavier versions of the electron.  CLVF, however, is a process that could produce tau-antimuon or muon-antitau pairs. CLVF has never been observed, but Li’s research provides theoretical calculations that future particle colliders, such as the Belle II in Tsukuba, Japan, and the BES III in Beijing, China, could use to produce CLVF.

Li was lucky enough to have two advisers: his research advisor at Wayne State, Alexey A. Petrov, and Haverford’s Assistant Professor of Physics and Astronomy Daniel Grin. Up next, he will continue his physics research as a Ph.D. student at the University of California, Santa Cruz, starting this fall.

“I am the first person in my family to go to college. I would like to thank QuestBridge for introducing me to Haverford,” he said. “I would also like to thank the Haverford College Fencing Team, especially Amanda Soled ’18, for providing the support I needed throughout my time at Haverford.”


What did you learn working on your thesis?

The most important skill I learned by working on my thesis is long-term project management. There were many directions and many levels of depth that my thesis could have gone in, but given the time constraint of one year, I had to make choices about the areas of particle physics on which I wanted to focus, and the level of sophistication with which to explore those different areas. The end goal is to produce a coherent thesis that stands by itself as an independent document and that also stands on the shoulders of physics giants, citing the physics literature from the last century to the last decade.

What are your plans for the future and does your thesis have anything to do helping to guide your future career path?

I am interested in the absurdity of physics at the quantum level. Specifically, electron-positron collisions could have radically different outcomes depending on the speed at which the particles are collided. For example, at 0.999999986 the speed of light, there is a relatively low probability that they interact. But at a slightly higher speed, at 0.999999987 the speed of light, this probability increases by more than a thousand fold… This is very different from, say, the speed of a car in the daily commute, in which driving at 45 MPH is not an entirely new experience from driving at 44 MPH.

-Michael Weber ’19

Photo: Courtesy of KEK

“What They Learned”is a blog series exploring the thesis work of recent graduates.