The ALICE silicon pixel detector system

The Large Hadron Collider (LHC) is again reaching its startup phase at the European Organization for Particle Physics (CERN). The LHC started its operation on the 10^th of September, 2008 with huge success managing to sent the the first beam successfully around the entire ring in less than an hour after the first injection in one direction, and later that day in the opposite direction. Unfortunately, on the 19^th of September, an accident occurred during the 5.5 TeV magnet commissioning in Sector 34, which will significantly delay the operation of the LHC. The ALICE experiment will exploit the collisions of accelerated ions produced at the LHC to study strongly interacting matter at extreme densities and high temperatures. e ALICE Silicon Pixel Detector (SPD) represents the two innermost layers of the ALICE Inner Traing System (ITS) located at radii of 3.9 cm and 7.6 cm from the Interaction Point (IP). One of the main tasks of the SPD is to provide precise traing information. is information is fundamental for the study of weak decays of heavy flavor particles, since the corresponding signature is a secondary vertex separated from the primary vertex only by a few hundred micrometers. e tra density could be as high as 80 tracks per cm² in the innermost SPD layer as a consequence of a heavy ion collision. The SPD will provide a spatial resolution of around ≅12 μm in the rφ direction and ≅70 μm in the z direction. The expected occupancy of the SPD ranges from 0.4% to 1.5% which makes it an excellent charged particle multiplicity detector in the pseudorapidity region |η| < 2. Furthermore, by combining all possible hits in the SPD, one can get a rough estimate of the position of the primary interaction. One of the challenges is the tight material budget constraint (<1% radiation length per layer) in order to limit the scattering of the traversing particles. e silicon sensor and its readout chip have a total thickness of only 350 μm and the signal lines from the front-end to the on-detector electronics are from aluminum. In this thesis, I present my involvement in the ALICE SPD project, I summarize the design, the construction, and the testing phase of the ALICE SPD. My involvement in the ALICE DCS project is also presented. During the past years the ALICE SPD collaboration has carried out four testbeams. e primary objective of these testbeams was the validation of the pixel ASICs, the sensors, the read-out electronics and the online systems - Data Acquisition System (DAQ), Trigger (TRG) and Detector Control System DCS with their so^ware and offline as well. e pixel chip and sensor prototypes were studied under different conditions (threshold scan, different inclination angles with respect to the beam, bias voltage scan, etc.). Tests of thick and also thin single chip assemblies and chip ladders as designed to be used in the ALICE experiment were also performed. During and a^er the testbeams I developed so^ware to verify the data quality, to merge 2 data pixels offline, to correlate the spatial information from different planes, to run a complex offline analysis of the testbeam data, including hit maps, integrated hit maps, event by event analysis, efficiency, multiplicity, cluster size, etc. e prototype full read-out chain with two ladders, the DAQ, Trigger and DCS online systems with their so^ware and also offline code were tested and validated during the testbeams. Configuration, readout and control of the SPD is performed via the Detector Control System DCS. As a member of the ALICE Control Coordination ACC team, I had the opportunity to participate in the design, development, commissioning and operation of this system. I took responsibility for the database systems and developed mechanisms for configuring the Front end Electronics (FERO). e SPD has been used as a working example for other detector groups which adopted this approach. I developed and implemented a mechanism of conditions data archival and participated in the creation of data exchange mechanism between the DCS and ALICE offline. The DCS as well as data handling tools are described in the thesis. (Author)