Simulations of the ALPIDE CMOS Sensors in a Forward Calorimeter

Abstract

The newly proposed FoCal detector at the ALICE experiment is meant to enhance the understanding of the low momentum fraction x regions (10^(-5)) of the Parton Distribution Functions. The FoCal prototype, the mTower, is being developed and tested. In this thesis, virtual models of the prototype mTower geometry and the ALPIDE CMOS chips were recreated. Two separate methods, Allpix^2 and SimpDiff, were used to simulate electrons of 50, 100, and 150 GeV passing through the detector geometry. These simulations included effects of charge sharing, clustering, and digitisation. Results were obtained in the form of hit maps, event sizes, and cluster sizes, to be compared to test beam data. Results showed that the SimpDiff method generated more hits per event (~50%) and slightly bigger cluster sizes (~5%); hit maps were comparable with Allpix^2. The relative RMS (mean/RMS) of event sizes for both methods differs at most by 0.04, implying that the shapes of the event sizes implementations were very similar. It was found that SimpDiff had 26.4% less run time than Allpix^2, signalling that SimpDiff is a more practical method for simple physics simulations, whereas Allpix^2 has the capability of performing simulations with more advanced physics phenomena such as capacitive charge transfer and TCAD mesh implementation. While the method of charge sharing in the ALPIDE chips is known, the parameters of the distributions are not; as such, both methods should be compared to test beam data in order to decide which is better suited for any given situation.