U of T grad students making history at the Large Hadron Collider
Pair hunting dark matter, subatomic particles
Hass AbouZeid is starting to think about how to make something out of nothing.
The physics graduate student is close to the end of his PhD and is finishing a stint at the Large Hadron Collider (LHC), the world’s most powerful particle accelerator, where he’s been hunting a “heavy Higgs boson”— but more on that later.
What he do if he doesn’t find anything? Does he still get a PhD?
“The nice thing about science,” he says, “is that not having a result is a result. If I do a search and if, under the conditions of my search, we don’t find any heavy Higgs bosons, that’s important.”
AbouZeid, who works under the supervision of Professor Peter Kreiger, is one of six U of T students currently working at the LHC, a high-energy particle accelerator that runs in a 27-kilometre circular tunnel buried 100 metres below the surface of the earth underneath France and Switzerland. Operated by the European Organization for Nuclear Research (CERN), the LHC allows scientists to recreate the conditions that existed a billionth of a second after the Big Bang — and to study them in a controlled way.
The group of 3000 scientists working at the LHC made a splash last summer when they announced the likely discovery of the Higgs boson, the so-called “God particle” that gives other particles mass and makes life possible. Writing in the New York Times, Lawrence M. Krauss called the LHC, “one of the most remarkable intellectual adventures in human history.”
AbouZeid, as part of that adventure, works on the ATLAS experiment, one of seven at the LHC. He’s looking for a different kind of Higgs particle — a heavier Higgs that, if discovered, would tell us that the Standard Model of physics isn’t sufficient to explain the forces of the universe. (The Standard Model allows us to explain the universe, and predicts how the various forces that govern it should act. But scientists don’t know why it works — or if it alone is enough to explain the universe.)
The Higgs boson isn’t the only mystery that the LHC might help solve.
Steven Schramm, also a physics PhD student working on the ATLAS experiment, is searching for dark matter, the mysterious stuff we know makes up 84 per cent of all matter in the universe — yet can’t be observed.
“We know almost nothing about the properties of this elusive phenomenon,” says Schramm, who works with supervisor Professor Pierre Savard. “We know that it feels gravity, but we don’t know if it interacts through any other force. Several theories, such as supersymmetry, predict the existence of dark matter candidates which interact through forces other than gravity.”
If dark matter does interact with a force other than gravity, scientists should be able to produce it in the particle accelerator.
Both students are aware that they’re part of a historic project. “It’s a fantastic experience,” says Schramm. “I have the privilege of working together with world-class experts, and the opportunity to contribute to the fundamental understanding of particles and their interactions.”
AbouZeid recounts his first impressions when he arrived at CERN as a summer student: “It’s a village. There are dorms for people who are coming for short-term stays, there’s a cafeteria where everyone has a coffee. On a warm day we go out on the patio for a beer. There’s a lot of people who are very good at what they do and very interested in what they do, which is a great combination.”
In the midst of all the talk about paradigm-shaking discoveries, AbouZeid points out that life at the LHC is not all about high-level research.
“Everybody has to devote some time to the upkeep of the experiment,” he says. “We’re on call one week per month. If any problem happens, day or night, we get a call. It could be a problem with data quality, the computer system’s reading of the data, a problem with the physical hardware, temperature problems, a certain piece of electronics not working. We have to keep it running full time.”
Even though no result is a credible result, AbouZeid is hoping to find his heavy Higgs particle. But, he says, “people always joke that making a big discovery during your PhD is the best way to extend your PhD, because you have to double and triple check your results. If I help discover something I’ll be here for a long time!”