Detecting Atmospheric Muons Underground
Date: Summer 2012
My school has a Cosmic Ray Club where we do experiments with cosmic rays through QuarkNet. For the 100th anniversary of the discovery of cosmic rays by Victor Hess, our teacher gave us assignments to find out the current status of research. I an reading about the investigations in high energy physics at CERN, and they use the ALICE detector to measure atmospheric muons. How can this be done seeing that the detector is about 100 m below the Jura mountains?
The Jura Mountains are composed of layers arising from convergence of the Alps and plate subduction. Shale, volcanic and limestone layers are the principal mix at the CERN site in the valley. This is great for muon study, but pose real challenges for the cavern construction design teams.
Muons are of high energy and move at relativistic speeds. They easily penetrate rock and water. ALICE has many detectors housed in a Compact Muon Solenoid weighing about 12,500 metric tons. There are three muon detector types; drift tubes measure ionization of the trajectory, cathode strip chambers and resistive plate chambers are in the end caps measuring momentum. These detectors are interspersed with iron yokes. Those muons can really penetrate!
The principle studies are of muons arising under controlled conditions from the LHC. However, atmospheric muons will be studied and discerned from the LHC muons by trajectory.
Hoping this helps!
Peter E. Hughes, Ph.D. Milford, NH
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Update: November 2011