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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Parsons has not found evidence of supersymmetry yet. The gravitino he thought he saw? He concluded it was a fluke.

This is a familiar story. In the past year, scientists at the LHC have published dozens of papers detailing their searches for sparticles. None have turned up gravitinos, selectrons, or squarks — only statistical blips, hiccups, and quirks.

Critics say this is telling. The most popular versions of supersymmetry, which are the simplest and those with the broadest implications, predicted that sparticles would be discovered almost immediately after the LHC was turned on, much sooner than the Higgs.

How long could the search for supersymmetry go on? Could it be forty years, like the search for the Higgs? This is, in fact, the great fear of many physicists.

“Am I surprised that no evidence of supersymmetry has been found?” says Woit. “No. And if it isn’t found soon, the best outcome would be for theorists and experimentalists to shift their focus elsewhere. There are plenty of other questions they could be working on. We’ve only just begun to understand how the Higgs works. That could keep them busy for years.”

Few physicists have ruled out supersymmetry altogether. Some, including Parsons, say there remains a small possibility that sparticles could still be found in data that was produced before March, when the LHC was shut down temporarily to prepare for higher-energy experiments. A more likely scenario, he and other physicists say, is that sparticles will be found in 2015, when the LHC finally fires on all cylinders.

“There is a growing realization that if supersymmetry exists, it probably isn’t the version we expected,” says Parsons. “The question now is whether or not the entire concept is invalid.”

How long could the search for supersymmetry go on? Could it last forty years, like the search for the Higgs? This is, in fact, the great fear of many physicists. They worry that the LHC won’t find evidence of supersymmetry and yet won’t disprove it either, since it can always be argued the collider simply isn’t powerful enough to see sparticles. This could put the field in limbo, with some theorists spinning off what University of Minnesota physicist Mikhail Shifman recently warned would be “contrived, baroque-like, aesthetically unappealing modifications” of supersymmetry instead of breathing new ideas into the field.

“I would be thrilled if we could rule out supersymmetry and string theory,” says Greene. “People might think that sounds odd, since I’ve spent my professional life working on these ideas, but I’m not wedded to any theory. What I want is to find out something true about nature. Unfortunately, if no evidence comes through at the LHC, it won’t necessarily mean these theories are wrong.”

In the meantime, Parsons continues to run his analyses, looking for unusual photonic activity. To do this work, he logs on to the LHC’s website, downloads a few gigabytes of data to his laptop from a gymnasium-sized computer center in Switzerland, and runs statistical-analysis programs that he and his students created. He does this work on the subway, at home in his pajamas, and at the ice rink in suburban New Jersey where he plays hockey every Thursday night. Most days he does it in his office, a drab and sparsely decorated place littered with cardboard boxes — evidence of his constant travels between Morningside, Nevis Labs, and Geneva.

“If the gravitino exists, it’s good at hiding,” he says. “The only way to find it is to be patient. We’ve looked under the lampposts. Now we need to look in the dark corners.”

John Parsons is a professor of physics at Columbia. Since 1994, he has helped to lead the European Organization for Nuclear Research’s ATLAS experiment at the Large Hadron Collider, outside Geneva. He contributed to the discovery of the Higgs boson.

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