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How do you find a Higgs boson? A crash course. (+video)

Scientists are using the $10 billion Large Hadron Collider in their search for the Higgs boson. Understanding how it works explains why it has proven so hard to find the Higgs boson.

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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.

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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.  

The engineers who keep the machine going with such precision "are real magicians," says Dr. Sulak. 

The collisions take place about once every 50-billionths of a second.

"That means you have to look at these collisions every 50 nanoseconds and decide whether you want one or not," says James Proudfoot, a senior physicist at the Argonne National Laboratory in Argonne, Ill. "That's a huge challenge, because there's a prodigious amount of background" – detector signals from collision debris that researchers must sift through to pick out the truly interesting signals.

[Editor's note: The original version of this story gave the incorrect title for James Proudfoot's position at the Argonne National Laboratory.]

The signals of interest get stored for detailed analysis. And how do you know you have spotted a Higgs boson? Among other things, theory predicts that a decaying Higgs boson should produce an array of secondary particles gathered into five distinct groups, or channels. It's not enough to spot one or two, although that will suggest the hunt may soon be over. All five channels must be present, and in the predicted proportions.

If the proportions are off, or the number of channels is different, researchers certainly can claim a discovery, but it will be up to the theorists to figure out what it is.

On Wednesday morning, the world will get the latest official word from scientists at the European Organization for Nuclear Research (CERN) in Geneva as to what the data tells them and how confident they are in their results.


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