National Geographic : 2008 Mar
and, with all due respect, looks as if he belongs on a mountaintop in Tibet. Ellis explains that the Higgs field, in theory, is what gives fundamental particles mass. He offers an analogy: Different fundamental particles, he says, are like a crowd of people running through mud. Some particles, like quarks, have big boots that get covered with lots of mud; others, like electrons, have little shoes that barely gather any mud at all. Photons don't wear shoes-they just glide over the top of the mud without picking any up. And the Higgs field is the mud. The Higgs boson is presumed to be massive compared with most subatomic particles. It might have 100 to 200 times the mass of a pro ton. That's why you need a huge collider to produce a Higgs-the more energy in the col lision, the more massive the particles in the "We had a theory that started out beautiful and elegant," says Joe Lykken at Fermilab, "and then someone beat on it and made it really ugly." debris. But a jumbo particle like the Higgs would also be, like all oversize particles, unstable. It's not the kind of particle that sticks around in a manner that we can detect-in a fraction of a fraction of a fraction of a second it will decay into other particles. What the LHC can do is create a tiny, compact wad of energy from which a Higgs might spark into existence long enough and vivaciously enough to be recog nized. Building a contraption like the LHC to find the Higgs is a bit like embarking on a career as a stand-up comic with the hope that at some point in your career you'll happen to blurt out a joke that's not only side-splittingly funny but also a palindrome. You can take an elevator down into the LHC tun nel if you wear a hard hat and carry an emer gency oxygen mask. When I visited, I found a major construction project still under way, with all the usual sounds of blowtorches and 104 NATIONAL GEOGRAPHIC * MARCH 2008 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 trans formed 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 tril lions-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 com petitive. 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. Tact lessly, I asked Dave Barney, one of the CMS scientists, what would happen if something went wrong and a part was dropped. You know, splat.