The ATLAS experiment is currently measuring decays from proton-proton collisions with a maximum energy of 13.6 teraelectronvolts. Over the next few years, the LHC at CERN will undergo the largest upgrade since it was commissioned in 2009. When it will be restarted in 2029, the luminosity of the accelerator ring is expected to be five times the current value. Luminosity is the measure of the rate at which protons collide at the LHC. By 2040, the scientists involved in the ATLAS experiment want to collect ten times more data than before.
With this increase in data, more precise measurements of the properties of the Higgs boson and other parameters in the standard model are possible. In addition, the various theories that predict new phenomena and particles beyond the Standard Model can be put to the test. "In the future, we will be able to cast a wider net for the direct search for phenomena beyond the Standard Model - for example, for the detection of supersymmetric partners of the known elementary particles or for dark matter particles in the universe," explains Hubert Kroha, project leader of the ATLAS myon detector group at the MPP. "The HL-LHC will dominate high-energy physics until a new, even more powerful accelerator is built, which is currently the subject of intense debate."
Technical innovations in the ATLAS detector
The central track detector will be replaced by a detector consisting entirely of silicon modules.
- In the cylindrical central part of the ATLAS muon spectrometer, which allows high-precision measurements of the trajectories and energy of the muons, the previous muon drift tube (MDT) detectors in the innermost detector layer are being replaced by new so-called sMDT chambers with drift tubes of half the diameter.
- These chambers will be connected to a new generation of resistive plate (RPC) trigger chambers. Both can handle an order of magnitude higher particle count rates and have a ten times longer lifetime under irradiation at the HL-LHC than previous versions.
- The electronics of all detector elements, especially the muon detectors, as well as the trigger system must be completely renewed.
Fast decisions in the trigger system
The trigger system plays an important role in data recording and analysis at the LHC - and even more so at the HL-LHC. It decides which collisions with muons are relevant for evaluation in terms of their energy. This drastically reduces the amount of data to be processed.
In order to optimize the selectivity of the trigger decision, the working group at the MPP has developed a forward-looking concept. In future, the drift tube chambers responsible for precise muon energy measurement at ATLAS will also be used for the trigger decision, which must take place within a millionth of a second. The realization requires new readout electronics and fast algorithms for the reconstruction of the muon tracks by the trigger processors.
