A Data-Driven Approach to Mapping LZ's Electric Field

The LUX-ZEPLIN (LZ) direct-detection dark matter experiment employs a 7-tonne dual-phase xenon Time Projection Chamber (TPC) to detect rare events via prompt (S1) and delayed (S2) scintillation signals. For a given energy, the relative S1 and S2 yields are dependent on the electric field strength within the TPC. We can construct a data-driven 3D electric field model for the TPC to correct for these effects. I will describe the construction of such models, exploiting differences in field dependence between alpha, beta, and gamma decay sources. In particular, we construct a field model using the position-dependent S1 ratio of Xe131m and Po218. This data-driven model is a useful cross-check of finite-element field models and of field stability in time. The S1 ratio should depend on field strength in a universal way, making this work potentially applicable to other liquid xenon detectors.