By Steve Koppes
Photo courtesy of LHC/CERN
In The Hitchhiker’s Guide to the Galaxy, the humorous answer to the Ultimate Question of Life, the Universe, and Everything turned out to be an ambiguous “42.”
This summer, University of Chicago particle physicists and their colleagues at the Large Hadron Collider in Geneva announced the discovery of what may be the closest thing to a scientific counterpart of The Hitchhiker’s Guide’s whimsical figure. Their experiments revealed a new particle with a mass somewhere between 125 and 126 giga-electron volts, or 134 times the mass of the proton. This figure falls within the predicted range for the Higgs boson, which acquired a decidedly unscientific nickname—“The God Particle”—after the title of a book co-written by Nobel laureate Leon Lederman, the Frank E. Sulzberger Professor Emeritus in Physics.
Physicists at UChicago and elsewhere have chased the elusive Higgs boson for more than two decades. The University produced many of the leaders in theory and experimentation whose ideas and instruments have shaped the long quest for the crucial particle, at the LHC and at Fermilab near Chicago. Without the Higgs, theorists believe, the universe would contain no atoms, no elements, no stars, and no people.
The Higgs particle is named for Scottish physicist Peter Higgs, who sought to explain why some particles have mass and others don’t. Bagging the Higgs boson was the first big prize on the LHC research agenda. If the Higgs boson is indeed what LHC physicists have found, the discovery has, like “42,” its own ambiguous aspects.
“This is the beginning. We still don’t know what this thing is,” says Henry Frisch, professor in physics and a longtime member of the Collider Detector at Fermilab collaboration.
Finding a “missing piece” of modern theory
The new particle could be, as expected, the last missing piece of the Standard Model of particle physics, which describes the fundamental structure and behavior of ordinary matter. Or the particle could be something more exotic, such as a supersymmetric Higgs, offering insights into the mysteries of dark matter and dark energy, which together are thought to comprise 96 percent of the universe.
LHC physicists have searched for supersymmetry via multiple avenues, says James Pilcher, professor in physics. “So far all of these searches are coming up empty,” Pilcher says. “Maybe we haven’t been looking in the correct way so far. Maybe supersymmetry is hiding in some obscure corner that we haven’t been able to explore yet.”
Pilcher is one of six UChicago faculty members who belong to the ATLAS (A Toroidal LHC ApparatuS) collaboration at the LHC. Another is Melvyn Shochet, the Elaine M. and Samuel D. Kersten Jr. Distinguished Service Professor in Physics. Shochet agrees with Pilcher that discovering supersymmetric particles may take more time.
“String theory requires that there be supersymmetric partners of the particles that we know, but it doesn’t require that they be in the mass range that has been studied so far,” Shochet says. “It’s very early in the game, and there’s an awful lot to do.”
Another LHC leader with UChicago roots is alumnus Joseph Incandela, BS’81, MS’85, PhD’96, a professor of physics at the University of California, Santa Barbara, and scientific spokesman for the European facility’s other massive Higgs collaboration, called CMS (Compact Muon Solenoid).
UChicago ATLAS collaborator Frank Merritt, professor in physics, notes that over the last several decades, much of the progress made in particle physics has involved confirming details of the Standard Model, but a new era may be beginning.
“We’re getting to a point now where we’re certainly going to go beyond the Standard Model,” Merritt says. “We don’t know what we’re going to see. It might be supersymmetry, it might be something else, but it’s going to be a very exciting exploration.”
Particles on the grid
A key element of this exploration will be the grid computing methods developed at UChicago and Argonne National Laboratory, which already have played a critical role in the Higgs search.
The fictional Deep Thought computer in Hitchhiker’s Guide crunched numbers for millions of years before arriving at the cryptic answer “42.” It took scientists far less time to pinpoint the mass of their newly discovered particle from data collected since 2011, thanks to the grid computing methods used for analyzing their latest results.
Computation Institute director Ian Foster helped invent grid computing, which allows people to share computer power, databases, and other online tools autonomously and securely across organizational and geographic boundaries.
“Building directly on concepts, methods, and software developed at Argonne and UChicago—and, certainly, elsewhere—the LHC Computing Grid distributes petabytes of data worldwide to hundreds of sites for reconstruction and analysis,” observes Foster, the Arthur Holly Compton Distinguished Service Professor in Computer Science. “Without the LHC Computing Grid, the discovery could not have occurred.”