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Muons are a type of particle related to electrons. They arise out of the decay of particles produced by the collision of protons in the center of the ATLAS detector. The muons' signals enable inferences about which particles came out of the impact of the protons.
For that, the scientists use the muon spectrometer. It is the outermost part of the ATLAS detector and measures the energy and trajectory of the muons with high accuracy. To this end, the particles are deflected in a strong magnetic field, which is generated by gigantic superconducting magnetic coils. Through precise analysis of muon tracks, among other data, the scientists were able to discover the long-sought Higgs boson.
In order to measure the muon tracks, the physicists use so-called muon drift tube chambers (MDT). These consist of several layers of drift tubes, which are filled with a gas mixture of argon and carbon dioxide. Through reactions with the argon atoms, the muons leave behind tracks in the drift tubes. By means of a high voltage of around 3,000 volts between the tube wall and a central counting wire, these tracks are registered and converted into electronic signals.
The muon spectrometer is also responsible for the enormous size of the ATLAS detector: With around 1,150 MDT chambers and more than 350,000 drift tubes, it measures the paths of the muons that pass through – over a total area the size of a footbal field, to an accuracy of less than one-hundredth of a millimeter. The chambers were developed at the Institute and were in large part constructed there. All of the chambers were installed in the underground ATLAS hall in 2005 and 2006.
The discovery of the Higgs boson was a major step for particle physics. Yet the physicists involved with the ATLAS experiment want the particle collisions to coax out further exciting insights. For that, they need more data, and therefore more collisions of protons.
In the coming years, the LHC will be upgraded to meet that need. At the updated High Luminosity (HL)-LHC, not long from how, significantly more proton packets than before will be accelerated and brought to collision. Due to the higher irradiation, the components of the ATLAS detector must also be upgraded. The MPP is currently developing a new, improved design for the muon chambers as well as new electronic components.
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