The phase-II ATLAS pixel tracker upgrade: layout and mechanics.

The ATLAS experiment will upgrade its tracking detector during the Phase-II LHC shutdown, to better take advantage of the increased luminosity of the HL-LHC. The upgraded tracker will consist of silicon-strip modules surrounding a pixel detector, and will likely cover an extended eta range, perhaps as far as |eta|<4.0. A number of layout and supporting-structure options are being considered for the pixel detector, with the final choice expected to be made in early 2017. The proposed supporting structures are based on lightweight, highly-thermally-conductive carbon-based materials and are cooled by evaporative carbon dioxide. The various layouts will be described and a description of the supporting structures will be presented, along with results from testing of prototypes.