Qualification of the BCM1F detector for luminosity measurement in the CMS experiment

At the European Organisation for Nuclear Research (CERN), experiments aim at producing and studying rare physical interactions that result from particle collisions using the Large Hadron Collider (LHC). The key parameters to evaluate the performance of particle colliders for this purpose are the luminosity and the beam energy. The Luminosity is the characteristic quantity that provides a measure of the ability of a collider to produce a certain number of specific particle interactions. It is also important as it is used as normalisation in cross-section measurements performed in the scope of physics analysis. Therefore, high accuracy of the luminosity measurements is essential for the accelerator operation and for the analysis of the physics data. At the Compact Muon Solenoid (CMS) experiment, several detectors measuring luminosity are deployed under the responsibility of the Beam Radiation Instrumentation Luminosity (BRIL) group. One of these luminometers is the Fast Beam Conditions Monitor (BCM1F). The Run2 version of the detector was composed of a combination of Polycrystalline Diamond sensors (pCVD) and Silicon sensors (Si). However, during operations, silicon sensors showed better performance with respect to the diamond sensors that suffered from efficiency loss. As Long Shutdown 2 (LS2) of the LHC is going on, the BCM1F detector that suffers from radiation damage will be replaced by a newly built version based entirely on AC-coupled silicon sensors. C-shape modules and test-boards were produced and mounted with the new AC-coupled silicon sensors. Thus the need of a test beam campaign and a full characterization in order to study the performance of the new sensor design. The first chapter introduces the reader to the LHC and the CMS experiment, as well as LHC specific terminology and quantities. Chapter 2 presents the concept of Luminosity and its mea- surement within the CMS Experiment. Chapter 3 summarizes basic concepts of Silicon based detectors. A description of the BCM1F detector and the BCM1F signal chain is then provided in Chapter 4. Chapter 5 and 6 provide information about the DESY test-beam facility, the tested prototype and the data acquisition software framework. The BCM1F DAQ system integration is also discussed and implementations of dedicated tools are presented. Finally, in Chapter 7, sensor characterisation results are presented. A conclusion is drawn in Chapter 8 where a summary of the testbeam campaign and the analysis prospects are provided.