Muon Detectors

The muon detectors form the outermost part of ATLAS (right) and are organized in three stations surrounding the central and lateral parts of the experiment. The central stations (see figure below) are each made of overlapping rectangular modules forming a cylindrical structure surrounding the internal parts of ATLAS. The lateral stations are disk-shaped (with a hole in the middle), each disk being composed of trapezoidal modules that overlap radially with each other.

Brookhaven Lab is developing and testing the station that will lie closest to the interaction point. At a distance of seven meters from the interaction point, these muon detectors will be particularly vulnerable to the high radiation environment produced by the colliding high-energy protons.

A module of cathode strip chambers is composed of five panels of longitudinal or transversal strips (the cathode strips), with anode wires woven between the panels and glued with epoxy on the sides of the panels. The space enclosing the wires between the panels is filled with a gas mixture of argon and carbon dioxide.

The cathode strips are read out by electronics modules mounted on the detectors, and the collected signals are sent through optical fibers to the experiment’s control room for further processing.

Most of the particles that reach the muon detectors are “muons” (hence the name of the detectors), which are very similar to electrons but 200 times more massive. Unlike electrons, muons are not stopped by the first components of ATLAS, but zip through the inside parts of the experiment, to be detected by the muon detectors.

A team of physicists, engineers and technicians is testing the quality of cathode strip chamber components produced in industry. To achieve the required performance, for example, the distance between the planes needs to be uniform to within 50 microns. So the scientists make sure that no distortion of more than 50 microns is detected on the panel surfaces. The team is also testing the tensions of the wires to make sure the wires stay parallel to each other and the distance from the panel surface to the wire is constant along the wire.

Last Modified: December 3, 2007

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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