Speaker
Description
Precise and efficient vertex reconstruction is essential for the FCC-ee physics programme. Full end-to-end simulation provides a robust estimate of the detector performance. A key component in full simulation is the digitiser, which transforms Geant4 energy deposits into realistic signals in silicon pixel sensors. This can provide a direct link from sensor R&D to detector optimisation and physics performance. We present a digitisation algorithm that captures sensor-specific behaviour and delivers inputs for both sensor development and detector-level studies.
Accurately simulating the vertexing performance at FCC-ee requires a detailed digitiser that captures differences between sensor types and layouts by modelling charge sharing and signal generation at the sensor level. In a workflow refined within the DRD3 OCTOPUS project, TCAD and Allpix Squared are used to simulate the sensor behaviour. The resulting information is stored in a lookup table, which encodes the probability for a deposited charge to be collected by a given pixel in its vicinity. In FCC-ee full simulation in the Key4hep framework, the digitisation algorithm then generates pixel hits according to this mapping, inherently accounting for hit position and angle.
The simulated cluster size is validated by comparing grazing-angle measurements from the H2M sensor prototype with corresponding Key4hep simulations. Based on this, first results obtained with the algorithm are presented. Incoherent pair creation in beam-beam interactions drives the vertex detector hit rate, which in turn defines the readout requirement for candidate sensor technologies. By using lookup tables for various sensor layouts, realistic cluster sizes and thus pixel hit-rates are estimated. Finally, an outline is given on how this algorithm will provide input for systematic detector layout optimisation studies based on the achievable spatial resolution on hits as a function of hit position in the integrated detector model.