The ATLAS tracking system for HL-LHC

The current inner detector of the ATLAS experiment will be replaced with a new, all-silicon detector to cope with the tough environment of the High Luminosity LHC (HL-LHC). The instantaneous luminosity of HL-LHC would result in harder conditions for the detector: increase in occupancy, bandwidth and radiation damage. The Inner Tracker (ITk) will consist of an inner pixel and outer strip detector aiming to provide tracking coverage up to vertical bar eta vertical bar = 4. The layout of the pixel detector is now finalized with five layers of pixel silicon sensor modules in the central region and several ring-shaped layers in the forward region. Due to their radiation hardness, 3D sensors are a promising option for the innermost pixel layer while in the other layers planar sensors will be used. The required very high hit-rate capabilities, increased pixel granularity, extreme radiation hardness and reduced material budget call for a size reduction as compared to existing sensors, involving smaller pitch, reduced active thickness and lower power consumption. All hybrid detector modules will be read out by a new front-end chip, developed within the RD53 Collaboration, connected to the silicon sensors using bump bonding. From simulations, the ITk performance in terms of tracking and vertexing is expected to be similar or better than that of the current tracking system, despite being in a much harsher environment.