Description of Light Guidance in Dual Clad Scintillating Fibres for the LHCb SciFi Tracker

During the LHCb upgrade in 2019/2020, a new detector element will be installed that uses scintillating fibres (SciFi) to detect particle tracks, the so-called SciFi Tracker. To predict its performance, a single fibre simulation has previously been developed with the Geant4 toolkit. The simulation results are compared to measurements in order to tune the simulation parameters and gain an understanding of the underlying fibre properties. This note presents the relevant information obtained so far and new findings concerning the reflection losses in scintillating fibres.