Speaker
Description
Delayed photon signals remain an insufficiently constrained instrumental background in liquid xenon TPCs. One possible origin is nuisance photoluminescence (PL): absorption of 175 nm xenon scintillation photons by detector materials or surface contaminants, followed by delayed re-emission at near-UV and visible wavelengths. Recent studies at Nikhef R&D lab for Xe TPCs suggest that materials passing standard radiopurity and outgassing requirements may still fail optical-background requirements.
One of the materials that we have shown to PL is solder flux residue [https://arxiv.org/abs/2605.16845]. Resin- and rosin-based fluxes used in detector construction can leave behind PAH-containing residues after soldering and cleaning, producing measurable photoluminescence. These residues may remain as stains on soldered connections, dissolve into the bulk Xe volume, or exist in the detector as um-mm-sized flakes made during thermal cycling. Another detector material we have identified as photoluminescent is PEEK. Despite being widely considered a detector-safe structural polymer, its aromatic backbone is capable of producing PL emission under VUV excitation.
These studies motivate broader material screening and guidelines for material cleaning and handling for XLZD. Delayed photon backgrounds may originate not only from materials but also from contamination introduced by material preparation, cleaning and handling during assembly. We present examples of materials observed to photoluminesce under UV and VUV illumination and make suggestions for future XLZD cleanliness and screening strategies.