You can take an elevator down into the LHC tunnel if you wear a hard hat and carry an emergency oxygen mask. When I visited, I found a major construction project still under way, with all the usual sounds of blowtorches and metal saws. Workers were installing magnets. They’ve since completed the process, having installed more than 1,600 magnets, most half the length of a basketball court and weighing more than 30 tons.
Oddly enough, none of those magnets will accelerate particles. The acceleration will come from electrical waves in a separate apparatus that boosts particles around the ring. The job of the magnets is to nudge the beams of particles to bend ever so slightly around the ring. Lots of particles moving at nearly the speed of light have only one desire in life: to keep moving straight ahead. So the bend needs to be gradual—thus the 17-mile circumference of the ring.
When the particles collide, they’ll produce showers of debris as their energy gets transformed into mass. The physicists won’t see the Higgs itself in that shower, but two of the four major experiments that the LHC will perform are capable of recording the detritus of the disintegrating Higgs—the telltale signal that a Higgs is decaying. And the assumption is that only the rare collision—one among many trillions—will produce a Higgs. Most collisions won’t result in anything terribly interesting. The particle—or rather its debris—will show up in a detector’s computers, found by sorting through massive amounts of data measured in petabytes—thousands of trillions of bits.
A major issue for CERN is how to decide that they’ve found the Higgs. How much proof do you need? They’ve got two experiments competing to find the same particle. Do they announce the discovery by one experiment even if the other hasn’t confirmed it yet?
The relationship between the ATLAS and CMS experiments is like Coke versus Pepsi. They’re working the same side of the street, but with different techniques. And they’re highly competitive. The day I went to see ATLAS, the man in charge, Peter Jenni, found out that I’d already seen the CMS experiment. “Now you’ll see something bigger,” he said. His voice carried a slight my-detector-is-better-than-yours tone.
CMS was built at the surface and will be lowered in several large chunks down through a shaft into a cavern along the tunnel. Tactlessly, I asked Dave Barney, one of the CMS scientists, what would happen if something went wrong and a part was dropped. You know, splat.