A 27-km underground loop of magnets beneath a tranquil patch of farmland in Europe will soon go to work on the universe’s deepest mysteries.

For a research physicist, Sandra Ciocio knows all about the trials of the construction site. In recent years she’s seen 7,000 tons of sensitive equipment lowered down a 100-m shaft to prepare for a single grand experiment. The technology was groundbreaking and the schedule punishing. “It’s been deadline, deadline, deadline,” she says. “I haven’t had a holiday in five years.” But when the first real data begin to emerge this summer, the possible rewards should be worth the effort: a final explanation of one of the last puzzles of physics. “I feel like crying,” says Ciocio. “It’s like a dream come true.”

Deep beneath a tranquil patch of farmland, Ciocio and her colleagues at the European Organization for Nuclear Research, known as CERN, have built the world’s biggest and most sophisticated scientific instrument, the Large Hadron Collider, housed in a 27-kilometer tunnel that loops beneath the French-Swiss border. Using unprecedented energy, it will re-create the conditions a fraction of a millisecond after the big bang that gave birth to the cosmos 14 billion years ago. The goal: to track down a single elusive particle whose existence — if it can be proved — would fill a critical gap in our understanding of the universe.

This particular mystery has a daunting history. More than 30 years ago scientists developed an elegant series of equations, called the Standard Model, that describes the make-up of the universe in terms of the relationship between a few fundamental particles and forces. But the model has gaps. One gap is the baffling issue of mass. Why are some particles heavy while others have no mass at all? According to the leading theory, the weight of a particle depends on how it interacts with a mysterious “Higgs field” that permeates all space. So far scientists haven’t found any evidence that this field — and its associated particle, the Higgs boson — exists. They’ve been waiting for a particle collider big enough to perform the necessary experiments. The Large Hadron Collider was built to fit this bill.
The idea behind the collider is simple: get protons — positively charged particles present in every atom — going fast, crash them into each other and observe the fragments. The LHC will use superconducting magnets to guide the protons round and round the subterranean ring until they’re going almost as fast as light. The resulting collisions will release unprecedented amounts of energy (equivalent to 100,000 times the temperature at the center of the sun). With luck, they’ll also produce, among a shower of lesser particles, the long-sought Higgs boson.

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