COMMISSIONING OF ATLAS AND EARLY MEASUREMENTS WITH LEPTONS IN ATLAS AND CMS

on behalf of ATLAS and CMS collaborations With only a few months until the LHC start-up, the commissioning of ATLAS is in its final stage as the last components of the detector are installed. The understanding of the detector response acquired during the preparation phase is presented as well as the expected perfor-mance at start-up. The strategies of both ATLAS and CMS regarding the use of early data involving leptons is then described. Assuming an integrated luminosity of 100 pb−1 in 2008, examples of calibration procedures and early measurements are given. 1 Commissioning of ATLAS At the time of this paper, everything except the endwall muon chambers has been installed. In this section we summarize the acquired understanding of the detector performance before start-up. 1.1 Detector status at start-up The endwall muon chambers are the last components to be installed in the cavern (June 2008). With the full magnet tests performed soon afterwards in order to check the endcap toroids at their nominal field, the entirety of the ATLAS detector will have been assembled ready for the first collisions. Data taking has already been tested with cosmic rays throughout the two preceeding years of commissioning as the different detectors have been installed. The complete acquisition and processing chain has been successfully exercised from the primary site at CERN and throughout worldwide distributed sites. 1.2 Inner detectors The commissioning of the Inner Detector was initiated on the surface where cabling checks and debugging were performed. Once in the cavern, the noise levels were the same as those measured on the surface. The global alignment between the silicon strip (SCT) and transition radiation (TRT) trackers was measured with reconstructed cosmic ray tracks (as shown in Fig.1), where the results were consistent with precision survey measurements. Little time was available for cabling cross-checks of the innermost layer of pixels which was cabled just before ATLAS was closed. The number of non-working channels was measured to be small (0.3%)