The Impact of Incorporating Shell-corrections to Energy Loss in Silicon

TL;DR

This paper introduces an improved silicon energy loss simulation incorporating shell-effects via the Bichsel straggling function, enhancing the accuracy of thin sensor modeling for detector design and data comparison.

Contribution

The authors developed and integrated a shell-corrected energy loss model into Geant4, improving the realism of thin silicon sensor simulations compared to traditional Landau-based models.

Findings

Enhanced simulation reproduces more realistic position resolution degradation.

Bichsel and PAI models produce similar results above a few microns.

Below a few microns, PAI does not fully capture shell effects.

Abstract

Modern silicon tracking detectors based on hybrid or fully integrated CMOS technology are continuing to push to thinner sensors. The ionization energy loss fluctuation in very thin silicon sensors significantly deviates from the Landau distribution. Therefore, we have developed a charge deposition setup that implements the Bichsel straggling function, which accounts for shell-effects. This enhanced simulation is important for comparing with testbeam or collision data with thin sensors as demonstrated by reproducing more realistically the degraded position resolution compared with na\"{i}ve ionization models based on simple Landau-like fluctuation. Our implementation of the Bichsel model and the multipurpose photo absorption ionization (PAI) model in Geant4 produce similar results above a few microns thickness. Below a few microns, the PAI model does not fully capture the complete shell effects that are in the Bichsel model. The code is made publicly available as part of the Allpix software package in order to facilitate predictions for new detector designs and comparisons with testbeam data.