Calibration of the HMPID detector at the ALICE experiment
Master thesis
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https://hdl.handle.net/11250/3070215Utgivelsesdato
2022Metadata
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Sammendrag
The ALICE ("A Large Ion Collider Experiment")-experiment at the LHC ("LargeHadron Collider") at CERN is an experiment with the prime aim being investigating interaction forces of particles at extreme temperature and energy density. [12] The ALICE experimentconsists of several detectors, with the HMPID ("High Momentum IDenfification") beingthe detector able to identify particles with the highest momentum. [87]The HMPID has seven chambers; in each chamber, there are three radiator vessels and sixHV ("High-Voltage") sectors. [32, p. 38][39]MotivationThis thesis documents the migration of code for calibration of the HMPID from the oldframework (AliRoot), to the new, O2 ("Offline Online Processing").The calibration procedure calculates the radiators’ refractive index in the HMPID and theCharge threshold for each sector. The refractive index of the HMPID-radiators will, togetherwith the Cherenkov angle, yield the velocities of particles transversing ALICE. Together withenergy measurements obtained by Calorimeters at the ALICE experiment, this enables theidentification of particles through the particle’s mass. The charge threshold sets the thresholdfor which digits in spatial proximity will be included in clusters.Prior WorkThe calibration procedure has been done for the HMPID for the old framework in [19].Moreover, the calibration procedure has been done for other ALICE detectors in theO2-framework, the calibration for the TOF-detector can be found in [83].FrameworksBefore starting Run 3, the ALICE experiment moved away from the previous framework,AliRoot - which was used in Run 1 and 2 - towards O2 ("Online Offline processing").The new computing framework was developed to meet the computing resources needed inrun 3, where interaction rates are expected to increase 100-fold. Data flow to the O2 systemis ensured by the DCS ("Detector Control System") interface. [51]. Data in Run 3 forALICE is processed through the CCDB ("Condition and Calibration Data Base"). [86]Project OutcomeThe calibration will result in CCDB-objects, stored in the DCS of the O2 system. Theproject is finalized and will - subject to review and modifications - be part of the officialALICE-O2 project [17]. At the time of delivering the thesis, a code review was receivedpointing out some minor bugs related to the storing of objects in the central server of theCCDB; the process of writing and retrieving objects from the CCDB , however, work on alocal installation. The calibration procedure in the project will be used for both Monte Carlosimulations and for measured values in Run 3.