An Overview of the Atlas Particle Detector

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The ATLAS (A Toroidal LHC Apparatus) particle accelerator is a physics experiment taking place at the CERN Laboratory in Switzerland. Its focus is to find particles that other detectors are not capable of finding. Three thousand physicists from thirty-eight different countries participate in the experiment. The experiment began in 2007.

The accelerator called the LHC or Large Hadron Collider is a sixteen mile long pipe or closed curved surface. Particles, traveling at the speed of light, crash into an electromagnet weighing over 2,000 pounds and having the size of a house. The LHC consists of four major parts: the Inner Detector, the calorimeters, the muon spectrometer and the magnet systems. The magnet systems guide the other particles to the inner detector and the spectrometer at high speeds. This enables the collider to get the desired data. The physicists use bicycles to maintain the sixteen-mile loop.

The Inner Detector follows the charged particles to reveal what they are and how fast they move. It has three layers to identify the charged particles: the Pixel Detector, the Semi-Conductor Tracker, and the Transition Radiation Tracker. The Pixel Detector is the inner layer and uses silicon. The Semi-Conductor Tracker measures larger silicon and is the middle layer. The Transition Radiation Tracker is the outermost layer and it detects the tiniest particles with radiation and drift tubes.

Next are the calorimeters which measure energy. They are outside the Inner Detector. It has two systems. The two systems identify whether the particles are electromagnetic or hadronic.

The muon spectrometer tracks the weakest of particles. These muons are important part of understanding the whole idea of mass.

The magnet systems bend the path of the particles so physicists can measure the forward movements of the particles. The amount of curvature identifies what particles they are.  

The question this device will eventually answer is: why does everything have a different mass? By smashing different objects together, other objects or chemicals emerge as strange quarks, Z bosons, pi mesons, and Higgs bosons. The data that comes from the experiment will take many years to analyze as each minute it records twenty-seven CDs of information.

Milan Nikolic, a graduate student from UC Santa Barbara describes the building of the Collider, "It is actually in an underground river. We had to sink liquid nitrogen probes and freeze the river around it to lay the concrete structure down. . . It's like a five-story building."   It is a frightening piece of equipment. When not in use, it dangles from 300 foot shafts from four bundles of black cables.

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