Stacked like a set of Russian dolls, these subsystems record the energies and tracks of particles traveling through the detector. A powerful superconducting magnet—a cylindrical solenoid embedded in the detector—bends the paths of charged particles. The curvature of these paths allows scientists to determine the electric charge and mass of each incoming particle.
The goal of the Cosmic Challenge was to simultaneously test all the CMS detector subsystems with the solenoid switched on. It was the final test before moving detector components into their final location 100 meters underground in the tunnel of the Large Hadron Collider.
As part of the test, the CMS team cooled the solenoid to its operating temperature of about minus 270 degrees Celsius and powered it up. The magnet produced a field of 3.8 Tesla, strong enough to bend the paths of even the most energetic particles.
For a couple of months, the CMS team recorded cosmic rays and reconstructed their tracks. The graphic shows the curved path of a muon, a heavy relative of the electron, which traversed all four CMS subsystems on Sunday evening, August 27, 2006. A few hours later, Austin Ball, technical coordinator for CMS, wrote in the electronic logbook that the detector had achieved the goal of 10 million useful cosmic-ray events, give or take 50,000.
Today, the CMS solenoid and much of the detector are in the CMS collision hall, being assembled in time for the startup of the LHC. In the spring of 2008, the collaboration will again power up the magnet, this time preparing the detector for the recording of particles emerging from powerful proton-proton collisions.
