  The Light only Liquid Xenon (LoLX) experiment is a prototype detector aimed
to study liquid xenon (LXe) light properties and various photodetection
technologies. LoLX is also aimed to quantify LXe's time resolution as a
potential scintillator for 10~ps time-of-flight (TOF) PET. Another key goal of
LoLX is to perform a time-based separation of Cerenkov and scintillation
photons for new background rejection methods in LXe experiments. To achieve
this separation, LoLX is set to be equipped with photon-to-digital converters
(PDCs), a photosensor type that provides a timestamp for each observed photon.
To guide the PDC design, we explore requirements for time-based Cerenkov
separation. We use a PDC simulator, whose input is the light information from
the Geant4-based LoLX simulation model, and evaluate the separation quality
against time-to-digital converter (TDC) parameters. Simulation results with TDC
parameters offer possible configurations supporting a good separation. Compared
with the current filter-based approach, simulations show Cerenkov separation
level increases from 54% to 71% when using PDC and time-based separation. With
the current photon time profile of LoLX simulation, the results also show 71%
separation is achievable with just 4 TDCs per PDC. These simulation results
will lead to a specification guide for the PDC as well as expected results to
compare against future PDC-based experimental measurements. In the longer term,
the overall LoLX results will assist large LXe-based experiments and motivate
the assembly of a LXe-based TOF-PET demonstrator system.
