ATLAS Pixel Detector Design For HL-LHC

The ATLAS Inner Detector will be replaced for the High-Luminosity LHC (HL-LHC) running in 2026. The new Inner Detector will be called the Inner Tracker (ITk). The ITk will cover an extended eta-range: at least to |eta|<3.2, and likely up to |eta|<4.0. The ITk will be an all-Silicon based detector, consisting of a Silicon strip detector outside of a radius of 362mm, and a Silicon pixel detector inside of this radius. Several novel designs are being considered for the ITk pixel detector, to cope with high-eta charged particle tracks. These designs are grouped into 'extended' and 'inclined' design-types. Extended designs have long pixel staves with sensors parallel to the beamline. High-eta particles will therefore hit these sensors at shallow angles, leaving elongated charge clusters. The length of such a charge cluster can be used to estimate the angle of the passing particle. This information can then be used in track reconstruction to improve tracking efficiency and reduce fake rates. Inclined designs have sensors angled such that they point towards the interaction point, resulting in smaller charge clusters, multiple hits per layer of pixel sensors, reduce material, and thus reduced cost. The small clusters, and multiple hits per layer, can then be used in track reconstruction to improve tracking efficiency and reduce fake rates. Several mechanical solutions are also being considered for each of the extended and inclined designs. Thermal management, radiation-length mapping, and electrical services will also be discussed.