COVER STORY

Heady Collisions

Move over, Higgs boson. Columbia scientists at the Large Hadron Collider are searching for the key to a unified theory of everything.

by David J. Craig Published Summer 2013
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Illustration by Keith Negley

“Say it’s 3:00 a.m. and there’s a question about how reliably your electronics are working,” says Nikiforos Nikiforou, a Columbia PhD student who lives and works full-time at the LHC. “You might have to get your team down into the pit and run some diagnostic tests. Your job is to do whatever is necessary to make sure that detector is working smoothly at all times.”

Today, these Columbia physicists are helping to lead a major LHC renovation and upgrade. The $10 billion machine, which has already produced collisions four times as powerful as any in the past, is now being readied for even higher-energy collisions that will take place in 2015. The scientists expect that by smashing protons at faster speeds and in greater quantities they will more than double the amount of energy the collisions release per second. This could help find evidence of supersymmetry, scientists say, because most sparticles are hypothesized to appear only at higher energy levels than the LHC has reached so far.

“It seems that in the first moments after the Big Bang there was an elegant simplicity, a grand synthesis that shattered and eventually crystallized out into the messy world that we see around us.” — Brian Greene

“The higher the energy level, the further back you’re inching toward the conditions of the Big Bang,” says Parsons. “And every bit of progress can make a difference in the phenomena you see.”

Supersymmetry is not the only concern of the Columbia physicists at the LHC. Parsons, Brooijmans, Hughes, and Tuts have graduate students who continue to analyze the Higgs boson in order to better understand how it behaves. This work will continue for years. And some of the scientists are hoping to see familiar particles do unfamiliar things. Brooijmans is studying the top quark, which is among the more exotic of the seventeen known particles, to see how it behaves when shot out of collisions at nearly the speed of light.

“The top quark is the heaviest of the seventeen known particles, which means it is the one the Higgs binds to most strongly,” says Brooijmans. “It only existed naturally in the very first moments of the universe. But at the LHC, we’re able to produce several top quarks each second. If there exist particles that are heavier than those we’ve seen, it’s probable that they would decay into the top quark or interact with it. This could provide a window into all sorts of new physics phenomena.”

All of the experimental physicists interviewed for this article expressed at least mild skepticism that evidence of supersymmetry will be found at the LHC. But the prospect of learning firsthand whether nature follows the script written in the theorists’ notepads clearly excites them.

“Honestly, it’s what’s keeping me on the project,” says Hughes. “I’m the type of scientist who has always loved solving puzzles and supersymmetry is the most amazing half-finished puzzle. If you take it off the table, the field of particle physics just wouldn’t have the same allure for me.”

Tuts, who oversees four hundred ATLAS scientists as the project’s US operations program manager, will step down from that position this fall to return to his own research. He might look for evidence of extra dimensions, a component of most versions of supersymmetry and string theory. To illustrate the mind-bending concept, Tuts offers an analogy of a person who lives on a tightrope and whose only options are to walk forward or backward. Such would be a one-dimensional existence. But what if he could shrink down to the size of an ant? Then he would realize that his rope is filled with crevices into which he can crawl. Many theorists today suggest that our universe contains up to seven extra dimensions that likewise are too tiny for us to notice.

“If this were true, you might see particles disappear without a trace, suggesting they’ve slipped into another dimension,” Tuts says. “Do I think that’s likely? Not really. I personally find the concept a bit far-fetched. But I think you have to look for it. The potential payoff is just too big.”

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