Physicist Joe Incandela, AB’81, SM’85, PhD’86, had always been “50-50” on whether the Higgs boson would ever be found. By this past spring Incandela, who leads one of the two CERN experiments that searched for the particle-physics holy grail, knew that the data would soon verify the Higgs boson’s existence or rule it out.

On June 14 an excited researcher sent him a graph that pointed to confirmation. “Seeing that plot, I knew which way it was going,” Incandela says. “So I couldn’t sleep.”

He was restless because of the work ahead more than his excitement. As head of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider near Geneva, Switzerland, Incandela and his staff had just three weeks to pull together a presentation outlining the Higgs boson discovery. On July 4, he delivered the results alongside Fabiola Gianotti of the ATLAS project, which includes 28 UChicago scientists.

A physicist at the University of California, Santa Barbara, Incandela began a two-year term January 1 as the CMS spokesperson—the title given to the experiment’s chief scientist. He had served as deputy for the previous two years.

The Higgs discovery was not Incandela’s first experience with a major physics achievement. In the 1990s he was coleader of one of the Fermilab teams that first observed the top quark. But he had never been a part of such a massive undertaking.

Many had predicted its discovery since University of Edinburgh physicist Peter Higgs and four colleagues developed the theory in 1964. But finding the particle required billions of dollars and thousands of scientists from dozens of countries poring over data from particle collisions numbering in the thousands of trillions.

“It’s unbelievable what we pulled off,” Incandela says. “We all have specializations, and we don’t understand the whole thing. We all have a general sense of things, but the details are so incredible, there’s so many things pushed to the limit and so many brilliant people involved in making it work. If anything goes wrong, we’re out of business. If any one system did not work, we couldn’t have done this.”

Finding the Higgs boson, the 17th and presumably final particle in the standard model—the physics equivalent of the periodic table of elements—essentially validates the prevailing theory of how the universe works. Just as H2O molecules make up a body of water, Higgs bosons make up the Higgs field, which fills the universe and gives mass to particles as they interact with it.

A Higgs boson is too unstable to be observed. So the collider experiments searched for what physicists believed the particle would decay into. Other subatomic particles produce the same fragments, so researchers were looking for the slightest excess signal, amounting to just a fraction of a percent, indicating the presence of something other than previously known particles: the Higgs boson.

The data showed a 5-sigma signal, meaning there was a one-in-three-million chance that it was a random fluctuation. During Incandela’s presentation, he showed a graph revealing a slight bump at a mass of about 125 gigaelectron volts, the Higgs hiding place. Vivid confirmation to the 500 physicists in the crowd, they reacted as if Incandela held a Higgs boson in his hand.“When that slide came on,” he says, “the audience gasped.”

For the first time he paused to consider the magnitude of the achievement that had kept him up nights for three weeks. “It hit me then. When the audience gasped, I realized: This is real. This is a major discovery.”