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    The Making of a New Collider

    The biggest physics experiment ever, CERN’s new particle accelerator, goes live this summer.
    April 22, 2008
    27 kilometers of magnets
    The two beams of protons will speed through their underground tunnels at a site straddling the border between France and Switzerland.
    The tubes here house the high-power magnets that guide the beams.
    A side view shows the channels through which the beams will accelerate (openings at center of image, one with a cable dangling from it). These two pipes are surrounded by superconducting metal cables (not ­visible in this image) through which a tremendous electric current flows, creating strong magnetic fields that guide the protons around the LHC and then toward each other for the high-energy collisions. Two tubes for the liquid helium that cools the magnets are visible at the bottom of the cross section.
    CMS detectors
    The CMS is named for its compact magnet, called a solenoid because of its coiled shape, and for one of the particles it specializes in detecting, the muon. When protons collide inside the CMS, the magnet at its heart (metal collar) deflects the resulting subatomic particles so that their paths intersect with many layers of detectors.
    Layers of silicon tiles inside the inner tracker barrel, which nests inside the magnet, pinpoint the location of charged particles and measure their momentum.
    The protruding barrel of the piece below also fits inside the magnet’s hollow. The rings of gold-­colored boxes are muon chambers that will detect the particles.
    Picturing Higgs and Z Prime
    Data gathered inside the CMS and other detectors will be reconstructed as event visualizations like the hypothetical ones pictured here. In this image (and the one on the next page), the dots represent ionization signals left by particles traversing a detector. Software picks through the data to trace particles’ paths, represented as lines. The existence of newly observed particles is inferred if the products they decay into are detected. One of the particles likely to be detected by the CMS in its early days is called Z prime, says MIT particle physicist Steven Nahn; the evidence it leaves behind is thought to include two easy-to-detect particles, muons and electrons. The visualization is of a Z prime decaying into jets of energetic particles, represented by the rectangular beams.
    The image is a visualization of a Higgs boson decaying into four muons. The curly lines represent particles with low momentum that don’t reach the farthest detectors. Providing evidence of the Higgs boson, a hypothe­sized particle that is thought to explain why particles have mass, would be a major coup for the LHC.

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    Illustration by Rose Wong

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