Detector Development and Analysis Techniques for Finding Leptoquarks with the ATLAS Detector at the LHC

The LHC and its experiments at CERN constitute the largest particle physics research programme to date, allowing for extensive studies of the existing Standard Model and for potential evidence of physics beyond that of our current comprehension. This thesis presents an analysis technique to find third generation leptoquarks in high mass $\tau^+\tau^-$ final states. The sensitivity on the coupling strength of a leptoquark with a chosen mass of 1.5\,TeV (2\,TeV) is $g^2 = 6.61\substack{+1.13 \\ -0.95}$ ($g^2 = 10.98\substack{+1.92 \\ -1.65}$). This is calculated using the total transverse mass of an event, $m_\mathrm{T}^\mathrm{total}$. In order to enhance the accuracy of tests on the Standard Model and to broaden the potential for uncovering new realms of physics such as leptoquarks, the LHC will be upgraded to the High-Luminosity LHC. This thesis presents the development of the Optoboard System -- the part of the ATLAS new Inner Tracker (ITk) Pixel Detector readout system that handles the transfer of data, command and trigger between the modules and the backend. All ITk Pixel Detector modules are assigned and mapped to the Optoboard System with Twinax cables length between 3016\,mm and 5776\,mm. Compatible with requirements in data transmission reliability, the Optoboard System is validated first with jitter measurements and bit error rate tests, reaching the desired $BER_{95%} < 2.7 \times 10^{-12}$ and second, with Sr-90 radiation at the ITk Pixel system test site with the Outer Barrel demonstrator.