High Rate Proton Irradiation of 15mm Muon Drifttubes

Future LHC luminosity upgrades will significantly increase the amount of background hits from photons, neutrons and protons in the detectors of the ATLAS muon spectrometer. At the proposed LHC peak luminosity of 5*10^34 1/cm^2s, background hit rates of more than 10 kHz/cm^2 are expected in the innermost forward region, leading to a loss of performance of the current tracking chambers. Based on the ATLAS Monitored Drift Tube chambers, a new high rate capable drift tube detecor using tubes with a reduced diameter of 15mm was developed. To test the response to highly ionizing particles, a prototype chamber of 46 15mm drift tubes was irradiated with a 20 MeV proton beam at the tandem accelerator at the Maier-Leibnitz Laboratory, Munich. Three tubes in a planar layer were irradiated while all other tubes were used for reconstruction of cosmic muon tracks through irradiated and non-irradiated parts of the chamber. To determine the rate capability of the 15mm drift-tubes we investigated the effect of the proton hit rate on pulse height, efficiency and spatial resolution of the cosmic muon signals.