ATLAS Silicon Pixel and Strip Detector: Commissioning with Cosmic Data

The ATLAS detector at the CERN Large Hadron Collider (LHC) started taking data in autumn 2008. In the innermost part of the detector, high-resolution silicon pixel and microstrip sensors provide excellent momentum and vertex measurement. These two silicon detectors, Pixel and SemiConductor Tracker (SCT), were successfully installed inside ATLAS in 2006-2008. After connection of cooling and services and verification of their operation, the detectors are now in the final stage of the commissioning phase. An extensive period of calibrations and cosmic ray data taking was undertaken in 2008, recording more than 400,000 tracks in the Pixel Detector and 2 millions in the SCT. By the end of the year, more than $96\%$ of the Pixel Detector and $97\%$ of the SCT were calibrated and taking data. Cosmic ray events were used to align the detector, check the timing of the front-end electronics and measure the performance.