The ATLAS Strip Detector System for the High-Luminosity LHC

The ATLAS experiment at the Large Hadron Collider is currently preparing for a major upgrade of the Inner Tracking for the Phase-II LHC operation, scheduled to start in 2026. The radiation damage at the maximum integrated luminosity of 4000/fb implies integrated hadron fluencies over 2x1016 neq/cm2 requiring a complete replacement of the existing Inner Detector. An all-silicon Inner Tracker (ITk) is under development with a pixel detector surrounded by a strip detector. The current prototyping phase, targeting an ITk Strip Detector system consisting of four-barrel layers in the center and forward regions composed of six disks at each end. With the production of modules scheduled to begin in 2020 and after successfully passing the Final Design Review, a thorough understanding of the current prototype modules is critical. In this contribution, we present the design of the ITk Strip Detector and outline the current status of R&D and prototyping on various detector components as well as reports on tests of prototype end-cap strip modules at DESY test beam facilities. The modules under study in test beams are irradiated and unirradiated so-called R0 modules, designed for the innermost region of end-cap wheels where radiation and occupancy conditions are the most severe. An R0 module is comprised of a sensor with glued-on readout hybrids and a power board. We will also present results from the first double-sided R0 prototype module, built using a carbon-fiber core with integrated services. The results focus on the detection efficiencies and spatial resolution of the modules, both in general and for specific regions of each module and to beam positions within or in between strips. The overall performance of the prototypes will also be discussed, for example relating detection efficiencies to noise occupancies.