Detection and Identification of Electrons and Photons - Applications in the ATLAS Experiment, for the ATLAS ITk Detector and at the DESY II Test Beam

It is important to exploit particle detectors for the detection and identification of electrons and photons in the best possible way, as it is adressed in this thesis by discussing three different application examples of precisely measuring electrons and photons at high-energy physics andtest beam experiments.Firstly, the optimization of the photon identification within the ATLAS detector at the LHCis investigated. Appropriate selection criteria are needed to efficiently discriminate prompt photons steming from the hard-scattering collision process from photons originating from hadronic jet decays. Systematic studies for the use of a multivariate optimization with a Boosted Decision Tree are presented and compared to the currently used rectangular cut approach.Secondly, the planned Inner Tracker (ITk) as an upgrade of the ATLAS detector for the HL-LHC is discussed. The focus of the investigations lies on the support structures foreseen for the silicon sensor modules, the petal core. The thermo-mechanical characterization of the petal is investigated using infrared thermography, dual-phase CO2 cooling and geometrical metrology, proving a well-performing design of the local support structure within the ITk detector specifications.Finally, measurements with multi-GeV electrons at the DESY II Test Beam Facility are presented to investigate the potential of the Material Budget Imaging technique. This technique aims to reconstruct the material distribution of samples by measuring the deflection angles of traversing electrons with the high-resolution EUDET-type beam telescopes exploiting the underlying effect of multiple Coulomb scattering. The results in terms of the determination of the characteristic radiation length of several materials as well as the two-dimensional material budget image of complex composite structures are shown.