Precision tracking at high background rates with the ATLAS muon spectrometer

Precision tracking at high background rates with the ATLAS muon spectrometer The ATLAS muon spectrometer performs to the specs of efficiency, occupancy and spatial resolution at present LHC peak-luminosities of $4 \times 10^{33}$ $\frac{1}{cm^2~s}$. Ten times higher peak-luminosities are envisaged after the LHC upgrade by end of this decade. Currently used tracking detectors in the most forward part of the muon spectrometer need to be replaced to cope with the expected huge background hit rates of up to 15~kHz/cm$^2$ to ensure muon trigger and precision reconstruction capabilities. Square meter sized micromegas or 15~mm diameter drift-tube detectors together with thin gap trigger detectors are under study as replacement. When exposed at our irradiation facility at the Garching Tandem accelerator laboratory, the track reconstruction efficiency and spatial resolution of 15~mm drift-tube detectors is robust against up to 20~kHz/cm$^2$ highly ionizing background hits. No signs of ageing were observed after accumulating an irradiation dose corresponding to 10 years of high luminosity LHC operation. For the micromegas detectors, which are intrinsically high rate capable, a single hit spatial resolution of 40~$\mu$m has been shown. Micromegas using resistive strip technology have been successfully operated unter $10^7$ Neutrons$/cm^2~s$ of 11~Mev. For the central part of the muon spectrometer, the installed monitored 30~mm diameter drift-tube detectors remain in place but may be operated using a considerably faster and linear drift-gas mixture. Such gas mixtures have been shown to be marginally sensitive to high photon fluences and do not age due to ionizing radiation.