As if to make matters more difficult, even though physicists speak of colliding beams of protons, in reality, the beams are mostly empty space. If an atom was the size of Earth, a proton in its nucleus would only measure about 2,000 feet across. The three quarks that typically make up the proton would be no more than four inches across, and probably a lot smaller, says Meenakshi Narain, a physicist at Brown University in Providence, R.I., and a member of the other team hunting for the Higgs boson.
Other processes go on inside the proton as well, but it's the collision among quarks and gluons, which binds the quarks -- that physicists are actually smashing.
At the LHC, the main show takes place in the collider's circular main ring, a racetrack with a circumference of nearly 17 miles and up to 300 feet below ground. But the facility also takes advantage of every type of particle accelerator developed in the past 115 years to first harvest the protons from hydrogen gas, then accelerate them incrementally through three increasingly powerful accelerators.
Only in the final stage do the protons reach energy levels high enough to allow the LHC's main ring to give them their final precollision energy.
Beams are made from bunches of protons – 100 billion protons to the bunch, and just over 2,800 bunches per beam. The large number of protons offsets the mostly-empty-space problem, significantly raising the probability of collisions.
Using powerful magnets to steer the protons around two lines running in opposite directions, the beams are at last brought into focus at each of two mammoth detectors the size of a cathedral's nave. This is where the collisions take place. By the time the beams are focused for collision, each is about half the width of a human hair. The detectors that track the collision debris must be able to locate the telltale debris trails to within half the width of a human hair.