The Quirks About Quarks: Grad Research

Thursday, March 12, 2015


Imagine being part of a group of 3,000 people worldwide, all working on the same project!

Thomas McCarthy & Gerald Oakham

McCarthy and Prof. Gerald Oakham

That’s what Carleton PhD student Thomas McCarthy is doing. He is part of a team of scientists working on the ATLAS experiment. Over time, a number of Carleton University graduate students, research associates, staff, and faculty members have also worked on this project.

ATLAS is a huge, multi-purpose detector — part of which was built at Carleton. It is located at CERN — a high-energy physics research centre near Geneva, Switzerland — and is one of two leading experiments associated with CERN’s Large Hadron Collider (LHC).

ATLAS physicists are probing our universe at the smallest, most fundamental scale, in order to understand what the tiniest building blocks of matter are and how they interact with one another.

ATLAS machine that found the Higgs boson

ATLAS machine that found the Higgs boson.

The focus of McCarthy’s research is a particle called the “top quark”.

Says McCarthy: “Quarks belong to a group of particles we believe to be fundamental. That means that, as far as we know, they can’t be broken down into smaller pieces. Quarks come in different ‘flavours’ with rather fanciful names: up, down, charm, strange, top, and bottom. The top quark was the last of this list to be discovered.”

“The properties of the top quark make up only a piece in the whole puzzle we’re trying to put together, but it’s a pretty important piece,” says McCarthy.

“The top quark is by far the most massive. It is even heavier than the recently discovered Higgs boson,” explains McCarthy. “And it is the mass of the top quark which we are measuring in our analysis. Although the top quark mass has previously been measured, our goal is to help pinpoint its value much more precisely.”

He points out that the large mass of the top quark has many implications as the mass is one of the most important properties of a particle. It ties it to other fundamental particles in the fabric of our model of the universe on a most fundamental scale.

The LHC at CERN can create top quarks. But once they are produced, they almost immediately decay into lighter particles. McCarthy and others are using ATLAS data to identify events where pairs of top quarks were produced and then infer their energies, before they decayed, through a series of measurements”.

Ultimately McCarthy says this type of fundamental research in particle physics could be likened to the pioneering research in electromagnetism in the late 19th century, or the study of quantum physics or general relativity in the early 1900’s.

“At the time, no would have been able to predict the resulting inventions of the light bulb, the photocopier, or GPS technology which came from those fields of research,” says McCarthy. “This sort of trail-blazing research is where we can make some of the most unexpected discoveries, so it’s a really exciting kind of research, but it’s hard to make concrete predictions about what will come as a result. That’s part of what makes it so exciting though.”

He also notes that there have been many spinoffs that have come from such research such as improvements to medical imaging, cancer treatment technology and the design of smaller and faster electronics.

McCarthy in the ATLAS control room

McCarthy in the ATLAS control room

McCarthy has been to CERN about 10 times. He says that every visit has been a fascinating learning opportunity. “Many of the world’s leading experts in high-energy particle physics are there, and conversations of the most revolutionary scientific nature could be taking place over something as casual as a cup of coffee at a table right beside yours. It truly is the ideal professional environment for a graduate student.”

head shot of Gerald Oakham

Gerald Oakham

McCarthy says he has been incredibly fortunate to work with Carleton Professor Gerald Oakham. “I have learned a great deal from him —many physics-related things but also much more than that in terms of things like communication, teamwork and time-management.” Oakham is the current chair of the Physics Department.

He says that it was Prof. Oakham who initiated the process which led him to spend a year in Munich at the prestigious Max Planck Institute of Physics. “I continue to collaborate with members from that group weekly (sometimes daily) on our top quark analysis, so there were a lot of great personal and professional contacts made through that experience.”

When asked if it can be difficult to explain his research to friends and family, McCarthy said: “I guess sometimes it can be pretty difficult to convey to others. With friends and family, it might only come up once in discussion and then the subject is never broached again. If you start with someone who’s genuinely interested, it can be much easier of course. Popular shows like the ‘Big Bang Theory’ or movies such as ‘Particle Fever’ have helped shed light on what particle physics is all about.”

His best advice? “If you know someone who’s studying particle physics, corner them at a party and ask them your best or even your most basic questions. On a certain level, you’ll undoubtedly stump them on some topic or another. And chances are you’ll both walk away having learned something.”

McCarthy hopes to graduate with his PhD this fall.

For more information about pursuing a PhD in Physics at Carleton, please go to our Grad Admissions website.

McCarthy and Carleton's ATLAS team

McCarthy with other members of Carleton’s ATLAS team