The 1984 film “Ghostbusters” provided many of us with our first glimpse of a particle accelerator. Sure, the movie’s “proton packs” were highly fictionalized and chock-full of pseudoscience, but their purpose was obvious: capture a negatively charged phantom by hitting it with a string of positively charged protons. Don’t cross the streams and you’re fine.
But what about in real life? The European Organization for Nuclear Research (CERN) operates the world’s largest and most powerful particle accelerator, the Large Hadron Collider (LHC). The minds behind the particle accelerator certainly didn’t build it to help capture ghosts, so what are LHC scientists looking for in their underground laboratories?
They are looking for something called the Higgs boson, a theoretical particle that exists as an excitation of the Higgs field. Particle physicists say this field exists throughout the universe, and that massless particles gain mass merely by passing through the field. Finding the Higgs boson could provide an explanation of why matter has mass and flesh out several cosmic mysteries.
First researchers have to catch the Higgs — and it’s one slippery phantom.
“It turns out that the Higgs particle is incredibly unstable,” says Tom LeCompte of Argonne National Laboratory, “so we only get to see it from its decay products. It falls apart moments after it’s created. So what we’re really looking for are the fragments.”
By analyzing the fragments, LHC researchers hope to piece together the Higgs. Yet, as with any scientific investigation, the outcome is never certain.
“In some cases we say, ‘Wait a second! We’re seeing a number of things that all look the same. This might be the Higgs boson, but it might be something else,’” LeCompte says. “You don’t really know when you start this kind of search what it is you’re going to find on the other side. Columbus thought he’d found a route to India, but it turns out he actually found something far more interesting.”
When scientists fire it up, the LHC accelerates two beams of particles close to the speed of light through a 17-mile (27-kilometer) ring of superconducting magnets. Each beam travels in a different direction, all inside a vacuum. It’s like Gomez Addams’ train set: Eventually there’s going to be a collision. Six different experiments, including LeCompte’s own ATLAS project, observe the collisions at four different points on the ring — and not everyone’s looking for the Higgs.
“You don’t want to think too much of the LHC as a single-purpose experiment designed to do just one thing,” LeCompte says. “It’s really more of an exploration of how matter behaves at the shortest distances and at the highest energy. When you have 3,000 people working on a project, they don’t all have exactly the same scientific interests.”
LeCompte stresses that the exact outcome isn’t guaranteed.
“If the Higgs is the right explanation of what’s going on, then it is almost certain that the LHC will see it,” LeCompte says. “So it’s almost guaranteed. The reason I say ‘almost’ is that if it’s just the Higgs by itself, we will clearly see it. But if the Higgs is part of a more complicated structure, we might at first miss pieces of that overall structure.”
For now, the Higgs remains elusive, but research continues at the $10 billion LHC facility beneath the French/Swiss border near Geneva. In fact, CERN is already planning a larger, even more powerful collider to carry on the research.