Detected an elusive subatomic particle which has been sought for over a decade: the single top quark.
"Look for a career that both challenges and interests you, rather than simply going for what is easiest or best paid. Difficulties and curiosity will ensure that you stay motivated and that you become good at what you are doing."
Dugan O’Neil and his co-workers were part of a group of particle physicists running an experiment called DZero. By the Fall of 2006, DZero had been studying top quarks for 11 years, but even after all that time had failed to find the elusive single top quark it had been looking for. Dugan O’Neil couldn’t care less about the seemingly endless drizzle outside his Burnaby, BC office. He and his graduate students were about to try a new computer program that might finally “see” the top quark buried within the data from DZero.
Particle physicists want to understand fundamentally what matter is made of at the smallest scales. They have learned that our world consists of tiny units, elementary particles such as electrons and quarks. The top quark, also called ‘the top’, is one of six known quarks. So far, however, the top had only ever been observed in pairs. The DZero physicists wanted to prove that the top can also exist in isolation, as a single top quark.
The trouble with finding the single top was that it emitted a very weak signal. Theory predicted exactly what that signal would look like in a particle detector but the signal was so weak and the background noise so intense that nobody had ever been able to detect it. Even though theory had been accurate so far, there was no experimental proof that the single top existed. It needed to be found to validate the theory. The scientists felt their best bet for finding the single top was by designing a smart computer program that will be able to identify the top within the overwhelming noise.
But what computer program should they use? No one knew for sure. O’Neil had a hunch, though. He attended a conference a few years back and something there caught his attention. Part of the conference was dedicated to a programming method called a ‘decision tree’. Decision trees specialize in separating signal from noise in a relatively simple and intuitive way. O’Neil felt that he could actually understand decision trees, and found this utterly refreshing in the otherwise quite convoluted world of advanced analysis techniques.
O’Neil thought that decision trees might even be better than a popular competing computer technique called neural networks. Decision trees are easier to understand and optimize, and they run very fast. But nobody had really proven that they could solve such a difficult problem. Working feverishly, the physicists spent many late nights at Simon Fraser University, training their decision trees with simulated data sets. Then, on that rainy night in 2006, the time had come to run the ultimate test. O’Neil was sitting beside his graduate student and post-doc in their office and the three were polishing the last bits of their program. So far, they had refused to look at any preliminary results the program might produce; they wanted to be sure everything was perfect before the final run. Finally, O’Neil’s voice broke the silence. He felt they were now ready to give it a try.
“So shall I just, you know, shall I run it?” he asked. “If I run it, the answer is going to come up. Shall I do it?”
“Do it,” his post-doc replied.
And so he did. He hit the button. The three held their breath until a number popped up on the screen in front of them. The number showed that they had a signal - just what they had been hoping for. After rigorous cross-checks from their DZero colleagues and a long internal review, they finally published a paper describing the first experimental evidence for the existence of single top quarks.
As a young scientist ...
O’Neil always knew that he wanted to be a physicist. He wasn’t the type of kid who liked to take apart radios, but he was captivated by science fiction and curious about everything that had to do with space. To understand these things, he concluded that he needed to learn the underlying physics. So when it was time to leave high school, the future was crystal clear. He would sign up for a physics degree at the University of New Brunswick. Studying physics had more to offer O’Neil than simply understanding the nature of things. For a boy growing up in a small town in rural New Brunswick, planning to become a physics professor was an exotic goal. “Most people work in much more industrial settings where I come from. So it was a bit weird. Maybe it attracted me for that reason,” he says.
He ended up majoring in particle physics almost by chance. At 19 O’Neil needed a summer job so he applied for research positions all across Canada. Michel Lefebvre, a young physics professor at the University of Victoria offered him a position. The invitation came as a bit of a shock. O’Neil had not expected it. He pulled out a map and was thrilled to discover that Victoria was on an island, a good place to spend the summer. Working with Lefebvre turned out to be a defining period in his career. Lefebvre became O’Neil’s mentor and PhD advisor and O’Neil has been working in particle physics ever since.
That same innocence and modesty still radiate from O’Neil’s boyish smile even today as an Associate Professor at SFU. When asked to describe himself, he says, “I have quite a calm personality. I rarely get angry, and I rarely get upset. But when we’re talking about things that I am very interested in, I get very enthusiastic about them.”
O’Neil has never regretted going into particle physics, although the field has its challenges. Most elementary particles only exist at very high energies and physicists obtain these levels of energy by accelerating matter to enormous speeds in gigantic circular underground tunnels. The Large Hadron Collider, the biggest particle accelerator in the world, has a diameter of 27 km. Because of the sheer size of the experiments, particle physics can only be done in huge collaborations. O’Neil typically works in groups of up to 3,000 scientists. Organizing this many researchers means rules galore and that can eat away at the freedom most professors enjoy. O’Neil however loves working in this environment. After all, collaborating on big particle physics projects means working with some of the smartest people in the world, something he would not want to miss.