Operation and performance of the ALICE silicon pixel detector with proton-proton beams

Abstract

Abstract The ALICE Silicon Pixel Detector (SPD) forms the two innermost barrel layers of the ALICE inner tracking system (ITS) and is made of hybrid silicon pixel detectors. The cell size is 50 μ m × 425 μ m and the SPD contains a total of about 107 readout cells. The two layers are located at average radii of 3.9 and 7.6 cm from the interaction point. The total material-budget of the SPD per layer is 1.14% X0. In addition of being a pixel detector with a very low material-budget in the sensitive area, the SPD is also capable of providing a fast trigger signal to contribute to the L0 trigger decision. The SPD has been installed in the experiment in 2007. Commissioning of the system was carried out in the following year, followed by several experimental cosmic runs in 2008 and 2009. The SPD was also operational during LHC beam injection tests as well as during the first beam collisions at the end of 2009. Since then the SPD has shown to be a key element of the ALICE experiment in providing data and trigger information. This presentation will review the experience gained during the commissioning of the detector and summarize the performance during the cosmic runs, LHC injection tests and first collisions.