Digital electromagnetic calorimeters for future collider applications

The LHC will run until \(\sim\)2040, after which time a new generation of particle colliders is anticipated. To measure the properties of known interactions at the LHC with greater precision, and to probe physics beyond the Standard Model, it is expected that a lepton collider will be constructed. This thesis focuses on the application of digital CMOS MAPS sensors to electromagnetic calorimetry at future colliders. Simulations of various geometrical configurations of a digital ECAL in the FCC-hh environment, a proposed 100TeV circular proton-proton collider, are presented. The optimal configuration using 50 silicon layers sandwiched between 0.6\(X_0\) thick layers of lead is found to provide an energy resolution of \(\frac{\sigma_E}{\mu_E} = \left(\frac{15.46\pm0.12\%}{\sqrt{E}}\right) \oplus (0.917\pm0.009\%)\). While this is a slightly poorer standalone resolution than the liquid argon baseline ECAL, this detector technology enables improved combination with information from the inner tracker due to its higher granularity, which may be required to mitigate the high pile-up regime in FCC-hh. Beam tests of a digital ECAL prototype with 48 ALPIDE sensors (EPICAL-2) are analysed. An event selection algorithm for EPICAL-2 is presented and its merits and performance are evaluated. The response of EPICAL-2 is analysed, and the intrinsic resolution from electron beam tests in the range 1--5~GeV found to be \(\frac{\sigma}{\mu} = \left(\frac{18.7\%}{\sqrt{E}}\right) \oplus (2.4\%)\) when a simple clustering algorithm is applied. The performance is also modelled in Allpix\(^2\) simulations, and the resolution from simulations found to be \(\frac{\sigma}{\mu} = \left(\frac{14.0\%}{\sqrt{E}}\right) \oplus (2.6\%)\). This is comparable to the CALICE analogue ECAL prototype and a significant improvement upon the resolution of the previous EPICAL-1 prototype. The lateral profiles of EPICAL-2 are presented and the maximum hit density for a 5~GeV electron beam is found to be \(\\approx\)300hits/mm\(^2\). Lastly, the forward-backward asymmetry of EPICAL-2 is examined and its causes identified using simulations