Search for charged Higgs bosons with tau-lepton signatures at the ATLAS experiment of the Large Hadron Collider and development of novel semiconductor particle detectors

Experimental High Energy Physics (HEP) studies are discussed in the context of exotic particle searches and data analysis techniques and the development and production of suitable detectors. The main covered topics span the aforementioned areas and are primarily related to the ATLAS experiment at the Large Hadron Collider (LHC). The Higgs boson discovery by the ATLAS and CMS experiments in 2012, solidified the Standard Model (SM), but at the same type provided a suitable probe for searches of new physics, beyond the SM (BSM). This thesis covers a study for a new particle, the charged Higgs boson, which is predicted by several BSM theories and its discovery would be a clear sign for new physics. The study was focused on the predicted $\tau\nu$ final state using a $36.1\,\mathrm{fb}^{-1}$ dataset of pp collisions collected at $\sqrt{s}=13\,\mathrm{TeV}$ with the ATLAS detector. No discovery was made, but new limits on relevant parameters were set. Studies that involve hadronically decaying $\tau$ leptons, such as the aforementioned charged Higgs boson search, are affected by background processes where quark- and gluon-initiated jets as misidentified as $\tau$s. A universal method for determining the impact of this background, and the associated systematic uncertainties, is being developed in ATLAS and is introduced in this thesis. The Large Hadron Collider (LHC) is presently preparing for the High-Luminosity upgrade that is designed to meet the current physics goals. The upgrade will result in more demanding conditions for the LHC experiments, in terms of higher particle fluences and larger collected data volumes, necessitating changes in their detector systems. The ATLAS inner tracker upgrade is discussed, focusing on the workflow and the quality assurance and quality control procedures necessary for the production of the strip modules that will be part of its new end-cap system in collaboration with industry. Neutron detection is essential for a wide range of neutron science applications and research. The evaluation of a novel boron-coated semiconductor with respect to its suitability of neutron detection is discussed.