Exploring quantum field, from sun’s core to Big Bang

Theoretical physicist William Detmold unlocks the mysteries of quarks, gluons, and their “strong interactions” at the subatomic level.

“With all of us stuck at home or in remote locations, I’m not sure that anyone is feeling particularly inspired right now, but this pandemic will eventually end, and sometimes getting lost in the intricacies of Maxwell’s equations gives a nice break from what is going on in the world,” says theoretical physicist William Detmold.

Photo: Jared Charney

How do protons fuse to power the sun? What happens to neutrinos inside a collapsing star after a supernova? How did atomic nuclei form from protons and neutrons in the first few minutes after the Big Bang?

Simulating these mysterious processes requires some extremely complex calculations, sophisticated algorithms, and a vast amount of supercomputing power.

Theoretical physicist William Detmold marshals these tools to “look” into the quantum realm. “Improved calculations of these processes enable us to learn about fundamental properties of the universe,” he says. “Of the visible universe, most mass is made of protons. Understanding the structure of the proton and its properties seems pretty important to me.”

Researchers at the Large Hadron Collider (LHC), the world’s largest particle accelerator, investigate those properties by smashing particles together and poring over the subatomic wreckage for clues to what makes up and binds together matter.

Detmold, an associate professor in the Department of Physics and a member of the Center for Theoretical Physics and the Laboratory for Nuclear Science, starts instead from first principles – namely, the theory of the Standard Model of particle physics.

The Standard Model describes three of the four fundamental forces of particle physics (with the exception of gravity) and all of the known subatomic particles.

The theory has succeeded in predicting the results of experiments time and time again, including, perhaps most famously, the 2011 confirmation by LHC researchers of the existence of the Higgs boson.

A core focus of Detmold’s research is on “confronting experimental data” from experiments such as the LHC. After devising calculations, running them on multiple supercomputers, and sifting through the enormous quantity of statistics they crank out – a process that can take from six months to several years – Detmold and his team then “take all that data and do a lot of analysis to extract key physics quantities – for example, the mass of the proton, as a numerical value with an uncertainty range.”

“My driving concern in this regard is how will this analysis impact experimental results,” Detmold says. “In some cases, we do these calculations in order to interpret experiments done at the LHC, and ask: Is the Standard Model describing what’s going on there?”

Detmold has made important advances in solving the complex equations of quantum chromodynamics (QCD), a quantum field theory that describes the strong interactions inside of a proton, between quarks (the smallest known constituent of matter) and gluons (the forces that bind them together).

He has performed some of the first QCD calculations of certain particle decays reactions. They have, for the most part, aligned very closely with results from the LHC.

“There are no really stark discrepancies between the Standard Model and LHC results, but there are some interesting tensions,” he says. “My work has been looking at some of those tensions.”

Inspired to ask questions

Detmold’s interest in quantum physics dates to his schoolboy days, growing up in Adelaide, Australia. “I remember reading a bunch of popular science books as a young kid,” he recalls, “and being very intrigued about quarks, gluons, and other fundamental particles, and wanting to get into the mathematical tools to work with them.”

He would go on to earn both his bachelors degree and PhD from the University of Adelaide. As an undergraduate studying mathematics, he encountered a professor who opened his eyes to the mysteries of quantum mechanics. “It was probably the most exciting class I’ve had. And I get to teach that now.”

He’s been teaching that introductory course on quantum mechanics at MIT for a few years now, and he has become adept at spotting those students who are similarly seized by the subject. “In every class there are students you can see the enthusiasm dripping off the page as they write their problem sets. It’s exciting to interact with them.”

While he can’t always bring the full complexity of his research into those conversations, he tries to infuse them with the spirit of his enterprise: how to ask the questions that might yield new insights into the deep structures of the universe.

/University Release. The material in this public release comes from the originating organization and may be of a point-in-time nature, edited for clarity, style and length. View in full here.