High-momentum final-state muons are amongst the most promising and robust signatures of physics at LHC. To exploit this potential, the ATLAS Collaboration has designed a high-resolution muon spectrometer with momentum measurement capability over a wide range of muon energies and angles. The conceptual layout of the spectrometer is based on the magnetic deflection of muon tracks in a system of three large superconducting air-core toroid magnets.
In order to obtain a high precision on the measurement of muon momenta up to the TeV order the ATLAS Muon Spectrometer is equipped with detectors with high spatial resolution (i.e. single-point resolution of order of 100 microns), perfectly calibrated and aligned with precisions of about 50 microns over distances of several meters.
The MicroMegas in the ATLAS Endcaps New Small Wheel
During the LHC Long Shutdown 1 (2018-2021) new detectors have been installed in the innermost layers of the two ATLAS Muon Spectrometer endcaps. These layers are the two so-called “New Small Wheels”: in spite of their name, each of them has a diameter of almost 10 meters and weighs more than 100 tons. They are equipped with two novel technology detectors: the MicroMegas and the Small-strip Thin Gap Chambers (sTGC); these detectors were designed to cope with the high-luminosity conditions of LHC Run-3 (ongoing since the year 2022) and Hi-Lumi LHC (that will start in 2030). The Rome group has taken part in the design and construction of the MicroMegas, then in their installation and commissioning with the first LHC Run-3 data.
The MicroMegas are micro-pattern gaseous detectors, that can sustain rates of tens of kHz per square centimetre, while keeping spatial resolutions of order 100 microns.
They are crucial for both muon first-level trigger and tracking, and will play a central role in the ATLAS Physics program of the present and of the future.
The Monitored Drift Tubes (MDT)
The MDTs are high-pressure aluminum drift tubes, that allow to reach a single-point resolution of about 90 microns. The tubes are arranged in multilayers and chambers and they are the main component of the ATLAS muon spectrometer, since the beginning of the experiment’s data taking.
The Rome group has collaborated since the beginning of the ATLAS collaboration to the design and construction of the MDTs, to their installation in the experiment and their calibration, and to the usage of the MDT measurements for the reconstruction of the muon trajectories, the playing a central role in all these steps. These chambers have contributed in a substantial way to all the major ATLAS discoveries, the Higgs boson included.
