The FASER experiment at the LHC aims to detect new, long-lived particles. To enhance its sensitivity, a high-resolution tungsten-silicon (W-Si) preshower detector was developed to distinguish closely spaced TeV-scale photons with separations as small as 200 \textmu m. The detector will utilize a monolithic silicon pixel ASIC, fabricated with 130 nm SiGe BiCMOS technology.
A notable contribution of this thesis is the development of a comprehensive simulation framework within the Allpix Squared software. The thesis details the characteristics of the signal and background expected from the new preshower detector, such as occupancy on the pixel ASICs, data rates to be handled by the readout system, charge distribution, and cases that could lead to misidentification of the electromagnetic shower cores. Variables such as total charge deposition, photon emission angle, and charge asymmetry are identified as potential candidates to discriminate dark matter signals from muon and neutrino backgrounds, with an estimation of the background rejection efficiency obtained by applying cuts on the data based on these variables.
Characterization of the pre-production ASIC was also performed and a current leakage was identified. Furthermore, characterization was also performed on the final production ASIC to evaluate the impact of pixel-to-pixel mismatch on charge measurement. The results are compared to those obtained in the pre-production ASIC to show the improvement in performance. Studies of the linearity of response of the flash ADC are also presented.
Moreover, the design and description of the calibration methods developed to identify and mask noisy pixels, set a sensitive working threshold, and offer a uniform charge response across the matrix are discussed. The impact of the calibration on the overall charge resolution is quantified. Three different methods of charge calibration are studied, and a final one is proposed.
A calibration module in Allpix Squared is also developed in this thesis. The final simulation system not only provides the simulated raw charge, but also the resulting ADC value based on the real behavior of the ASIC (or the simulated one), as well as the reconstructed calibrated charge, using the above selected calibration method.
In conclusion, the methodologies developed in this thesis, have contributed to the overall understanding and improvement of the preshower detector, paving the way for its successful installation into the FASER experiment at the LHC.
