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

Where do all the photinos, gluinos, squarks, gravitinos, charginos, zinos, and other sparticles figure in this story? They play bit parts, to say the least. Theorists suspect that few sparticles survived more than a nanosecond after the Big Bang, and they have no idea what most of them did then. In fact, their notion of these sparticles derives mainly from their efforts to mathematically accommodate the idea that nature’s forces once were unified. And what the mathematics requires is that every known particle has a supersymmetrical partner that resembles it except for being heavier and having a different spin. (A particle’s spin is an intrinsic quality related to the way it moves.)

If this strikes you as a bit too convenient, you’re not alone. Some physicists see it this way, too. Among the idea’s chief detractors is the Nobel-winning theoretician Sheldon Glashow, who once joked that supersymmetry must be right, since “half the particles have already been discovered.”

Peter Woit, a theoretical physicist who teaches at Columbia, likens supersymmetry’s adherents to Scrabble players who, disliking the letters they have been allotted, slip their hands into the bag for a few more. “The theory doesn’t identify previously unrecognized symmetries among real entities that we have in front of us,” he says. “All of its symmetries are between things we see in nature and imaginary entities. You need to regard a theory like that with some skepticism.”

MASTER KEYS

Far-fetched as supersymmetry might seem, large numbers of theoretical physicists and mathematicians have devoted their careers to developing the theory in recent decades. And it has proved useful in addressing many other mysteries. Take the problem of the universe’s total amount of matter: scientists say there is a discrepancy between the amount of known matter and the gravitational strength of celestial bodies. That is, if our galaxy were composed only of the elementary particles we are familiar with, it would not generate enough gravity to keep our sun and three hundred billion other stars orbiting its center. The discrepancy is glaring: scientists estimate that more than 80 percent of the universe’s mass has yet to be accounted for. Dark matter, so named because it is assumed to be unobservable, has been hypothesized to account for this discrepancy, and the invisible gravitino that Parsons is chasing is considered a leading candidate to be dark matter.

“It’s enormously striking that sparticles come with the properties necessary to make them candidates for the dark matter,” says Greene. “It didn’t have to be that way. Nature doesn’t always provide us such ready-made solutions. This is a wonderful case of a hand fitting into a glove.”

Supersymmetry is also a cornerstone of string theory, which hypothesizes that particles consist of tiny loops or strings of energy that vibrate at distinct frequencies. Because string theory offers a simple explanation for the characteristics of elementary particles and their interactions with the fundamental forces, it is regarded as a leading candidate for what scientists call a theory of everything. And it makes mathematical sense only when the total number of particles gets doubled.

Call that convenient. Or consider it a sign that Parsons and his colleagues at the LHC are on the cusp of glimpsing a hidden pattern in nature with tremendous explanatory power.

“It’s like what Einstein said of his concept of general relativity,” says Greene. “It seems too beautiful to be wrong.”

IT TAKES A VILLAGE

More than twenty Columbia physicists are now working at the LHC, which is overseen by the European Organization for Nuclear Research, or CERN, and lies three hundred feet below ground at the French-Swiss border. The physicists include doctoral candidates like Diedi Hu and Andrew Altheimer, who specialize in analyzing gigantic data sets; postdoctoral researchers like Emily Thompson, who studies dense plumes of energy, or jets, that sometimes shoot out of particle collisions; and undergraduates like Nilay Kumar, who is a whiz at writing computer code used in physics experiments. All of the members of Columbia’s LHC team, which is led by Parsons and fellow physics professors Gustaaf Brooijmans, Emlyn Hughes, and Mike Tuts, made important contributions to the discovery of the Higgs boson. Many are now involved in the search for supersymmetry.

“This is clearly the next hot thing,” says Hughes. “Most of my graduate students now want to look for sparticles.”

Columbia physicists developed many of the electronic components inside the Large Hadron Collider’s ATLAS detector, whose eighty-foot-tall cylindrical banks of magnets and sensors are often pictured in media reports. The scientists are now responsible for maintaining the equipment they made and for helping other physicists interpret the data generated by their instruments. Many of these components were designed and tested at Columbia’s Nevis Laboratories in Irvington, New York.

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